June 25-27, 2008 - Jackson Hole, Wyoming
Evaluation of a forecast model for tomato powdery mildew (Leveillula taurica) in central California
B. J. AEGERTER (4), C. Stoddard (3), M. Le Strange (6), C. Mickler (5), R. Davis (2), C. J. Rivara (1)
(1) California Tomato Research Institute; (2) Dept. Plant Pathology, UC Davis, Davis, CA; (3) UCCE Merced & Madera Co., Merced, CA; (4) UCCE San Joaquin Co., Stockton, CA; (5) UCCE Stanislaus Co., Modesto, CA; (6) UCCE Tulare & Kings Co., Tulare, CA
A model for predicting when to apply fungicides was developed by Guzman-Plazola et al. in 1995. In this project, the model was evaluated in commercial fields at ten locations in the San Joaquin Valley during 2006 and 2007. At each location, an automated weather station was placed within the field to record temperature, relative humidity and leaf wetness within the canopy. In replicated plots in each field, the fungicides myclobutanil (Rally) and pyraclostrobin (Cabrio) were rotated in applications timed according to a calendar schedule (14 to 21 day intervals), or according to model recommendations. Control plots received no fungicide applications. At the end of the season, severity of powdery mildew was evaluated in each plot. In 2006, two locations had no powdery mildew, while at five other locations there was a range of disease pressure from low to high. In 2007, there was an epidemic of powdery mildew in the Central Valley and all three field locations had moderate to high disease pressure. Over the ten trials, the calendar treatment averaged four sprays per season, while the model treatment averaged 2.5 sprays. At six of the eight locations where powdery mildew appeared, the calendar and model treatments provided a similar level of control, whereas at the other two locations the calendar treatment provided better control. At selected locations, we deployed a second set of sensors or a second weather station from a different manufacturer. The data suggest that using the model can reduce the number of fungicide applications but may not always provide the same level of control to that of calendar spray applications. Furthermore, we found that the model output is very sensitive to differences in the weather data, such as microclimate differences between nearby fields, sensor placement (in-canopy versus above), and type of weather station.
Screening different Brassica spp. germplasm for resistance to Rhizoctonia solani AG-2-1 and AG-8
E. Babiker (1), S. Hulbert (1), T. Paulitz (2)
(1) Dept. of Plant Pathology, Washington State University, Pullman, WA; (2) USDA-ARS, Washington State University, Pullman, WA
Poor stands of canola seedlings in Pacific Northwest (PNW) have been associated with Rhizoctonia solani AG-2-1 and AG-8. A total of eighty five genotypes of Brassica napus, B. rapa, B. carinata, B. juncea and Sinapsis alba were evaluated in the growth chamber for their resistance to both R. solani AG-2-1 and AG-8. The percentage of seedling emergence after seven days, survival of seedlings after twenty one days, shoot length, root length and disease severity were used as criteria for evaluation. R. solani AG-2-1 was highly pathogenic compared to AG-8. None of these genotypes exhibited complete immunity or complete resistance, but significant differences in susceptibility levels were observed. Three varieties: two hybrids from Germany (Flash and Sitro) and one open pollinated from Dekalb (CWH688), performed significantly better than others.
Effect of Ca on pink rot infection in potato
J. Benson (1), B. Geary (1), B. Hopkins (1), V. Jolley (1), J. Miller (2)
(1) Brigham Young University; (2) Miller Research
Phytophthora erythroseptica causes a disease known as pink rot in potatoes, which is responsible for substantial pre and post harvest tuber loss. Multiple factors such as nutrition, temperature, moisture, pH, cultivar susceptibility, and isolate resistance to fungicides contribute to yield loss. Many nutrients including Ca are associated with plant disease development and severity. The amount of Ca in the soil effects plant health and ability of P. erythroseptica to infect the host. Ca can act as a means to prevent infection and understanding the relationship of Ca on P. erythroseptica infection is essential to preventing disease outbreak. Russet Norkotah potatoes were grown hydroponically in association with the disease. The degree of infection was assessed by means on quantitative RT PCR. The effect of Ca on disease development was statistically significant at P = 0.0396. The pattern between Ca level and infection increased as Ca levels were reduced from 120 μmol to 1 μmol. A substantial decrease in infection was observed at 120 μmol.
Revus and Inspire: New fungicides for disease management
R. BOUNDS (2), A. Tally (1)
(1) Syngenta Crop Protection, Inc., Greensboro, NC, USA; (2) Syngenta Crop Protection, Inc., Visalia, CA, USA
Revus and Inspire fungicides, with the active ingredients mandipropamid and difenoconazole, respectively, received US federal registration in early 2008. Revus is a carboxylic acid amine (CAA, FRAC group 40) fungicide registered for use in numerous vegetables and grapes for control of late blight and downy mildew diseases. Revus is a reduced-risk product that offers excellent preventive activity by inhibiting spore germination. Difenoconazole is a de-methylation inhibitor (DMI, FRAC group 3) fungicide with current registrations in tomatoes, potatoes, sugarbeets, and apples. Inspire is highly active against powdery mildew, leafspot, and rust pathogens. Premixture products that include difenoconazole are in development for several crops, including vegetables, tree nuts, and grapes.
Residual effectiveness of fungicides in protecting rhododendron leaves from Phytophthora ramorum
G. A. CHASTAGNER (1), A. DeBauw (1), K. Riley (1), N. L. Dart (1)
(1) Washington State University, Puyallup, WA, USA
Over 20 fungicides have been tested in the last 3 years to determine their residual effectiveness in protecting Rhododendron × ‘Nova Zembla’ foliage from P. ramorum. Following application, leaves were periodically collected from fungicide-treated and untreated container-grown rhododendron plants for up to 16 weeks. Detached leaves were inoculated with suspensions of zoospores from an NA1 lineage rhododendron isolate by pipetting three 10-µl drops of zoospore suspension onto the lower leaf surface on each side of the leaf midrib. The leaf tissue was injured beneath 3 drops on one side of the leaf midrib using an insect pin. The tissue beneath the drops on the other side of the leaf were left unwounded. Checks included inoculated and non-inoculated leaves from untreated plants that had been sprayed with water. Leaves were then incubated for 7 days at 19°C. Fungicide efficacy was quantified by measuring the areas of the resulting leaf spots using ASSESS. No disease developed on any of the non-inoculated checks. The size of the leaf spots on fungicide-treated leaves was compared to the size of leaf spots that developed on the inoculated check leaves after each inoculation test. Results indicate that residues of some fungicides, such as captan, had very limited residual activity. On the other hand, residues of other fungicides such as cyazofamid significantly reduced disease development up to 12 weeks after application. Overall, the residual effectiveness of fungicides was greater on unwounded leaves.
Graduate A+: A new post-harvest decay control tool for citrus
A. COCHRAN (1), E. Tedford (2), R. Bounds (3), J. Adaskaveg (4), H. Forster (4), L. Kanetis (4)
(1) Syngenta Crop Protection, Inc., Granite Bay, CA; (2) Syngenta Crop Protection, Inc., Greensboro, NC; (3) Syngenta Crop Protection, Inc., Visalia, CA; (4) University of California, Riverside, Riverside, CA
Azoxystrobin and fludioxonil are newly registered ‘reduced risk’ fungicides for the postharvest management of green mold caused by Penicillium digitatum, the most important decay of citrus fruit, and some other decays. Both compounds are very effective by themselves against green mold. The high risk of resistance development in the pathogen against single-site mode of action compounds, as has been experienced with all of the older fungicides, however, instigated our evaluation of fungicide mixtures. In experimental packingline studies using inoculated lemon fruit, mixtures at 600 mg/L of each active ingredient were more effective in reducing decay as compared to single-fungicide treatments at 593 and 1000 mg/L, respectively. Decay was reduced from 86% incidence in the control to 0 to 3% in treated fruit. In addition, the mixture was very effective in inhibiting sporulation of the pathogen on infected fruit. This is critical, because decay will less likely spread during the sometimes long-term storage of lemon fruit and additionally, fewer propagules are exposed to resistance selection. A formulated pre-mixture under the brand name Graduate A+ is currently under development with an anticipated federal registration in 2009. This mixture product will represent a highly efficacious alternative in postharvest decay control of citrus fruit and represents an effective anti-resistance management strategy.
Novel delivery IPM tools in real time for decision support - pull
L. Coop (3), G. Grove (1), A. Fox (2), C. Daly (5), W. Mahaffee (6), C. Thomas (4)
(1) AgWeatherNet, Dept. Plant Pathology, Washington State University, Prosser, WA; (2) Fox Weather, LLC, Fortuna, CA; (3) Integrated Plant Protection Center, Dept. Botany and Plant Pathology, Oregon State University, Corvallis, OR; (4) National Plant Diagnostic Network, Dept. Plant Pathology, UC Davis, CA; (5) PRISM Group, Dept. GeoSciences, Oregon State University, Corvallis, OR; (6) USDA ARS, and Dept. Botany and Plant Pathology, Oregon State University, Corvallis, OR
The delivery of pest models for IPM is evolving rapidly, and should allow users to routinely access the data (pull approaches), or utilize tools that deliver the data to them (push approaches). The IPPC at OSU utilizes a pull approach to deliver a broad set of weather driven products that can be freely accessed by informed decision makers for all agricultural commodities. We have integrated 12,000+ weather stations with very-near real-time data ingest and delivery, dozens of insect, plant disease, weed, and crop models, PRISM based interpolation of temperatures and degree-days for the 48 state coterminous US, and Fox Weather LLC site-specific forecasts for OR, S. WA, and W. ID tied to 1,300+ locations. By combining actual and forecasted weather, we now have prototype virtual weather stations that are being tested to serve as a substitute for real weather stations, and for filling in missing weather data to mitigate data outages. The OSU IPPC system emphasizes end-user responsibility to examine model input data for quality assurance, and to understand which models they might need and how to use them. It serves in part as a test bed for new technologies developed by the Western IPM Weather Workgroup, for NW IPM needs, and for National Plant Diagnostic Network epidemiology needs.
Novel approaches to spatial and temporal estimation of diverse western meteorology
C. DALY (4), L. Coop (2), A. Fox (1), C. Thomas (3)
(1) Fox Weather, LLC, Fortuna, CA; (2) Integrated Plant Protection Center, Dept. Botany and Plant Pathology, Oregon State University, Corvallis, OR; (3) National Plant Diagnostic Network, Dept. Plant Pathology, UC Davis, CA; (4) PRISM Group, Dept. GeoSciences, Oregon State University, Corvallis, OR
A main goal of the Western Weather Workgroup is to foster the development of state-of-the-science weather and climate-based systems for agricultural decision making and other societal purposes. The western US, with its spatially complex weather patterns and sparse data density, presents unique challenges to this goal. Building on the unique capabilities of group members, the Western Weather Workgroup has taken novel approaches to the problem of providing accurate and timely simulation and forecasting of meteorological conditions at specific sites. Three approaches, addressing past, present, and future aspects of weather, respectively, are discussed here. The first approach is the recognition that there are repeatable patterns in the spatial complexity of western weather. The effects of terrain and other physiographic features leave an indelible climatological “fingerprint” on day-to-day weather. Therefore, accurate spatial data sets that represent long-term climatic conditions can provide critical guidance in mapping weather conditions, especially where data are sparse. The second approach is the idea that a “virtual weather station” can be created to simulate current meteorological conditions at a site, without the need for an actual observing platform. This requires a spatial climatological base, effective and timely ingestion of meteorological observations, and accurate interpolation of deviations of current observations from climatology. The third approach recognizes that effective planning and decision-making by weather-sensitive segments of society requires accurate and timely site-specific forecasts several days in advance. This requires a forecast system that can ingest coarse-grid forecast model results and downscale them to spatial scales that match the needs of agricultural users. Ideally, the system would have a strong climatological basis, but be sensitive to subtle meteorological patterns that make up today’s weather patterns. Examples of each of these three approaches will be presented.
Initial assessment of genotypic diversity of Phytophthora ramorum associated with Washington state ornamental nurseries
N. L. DART (1), G. A. Chastagner (1), K. Coats (1)
(1) Washington State University
Isolates (65 total) of P. ramorum were obtained with help of Washington Department of Agriculture from 13 nurseries, two streams, and one landscape situation in Washington state and genotyped using 4 previously developed microsatellite markers (Prospero, 2007). Three previously described lineages, known as EU1, NA1 and NA2, (Ivors, 2007) were detected in Washington nurseries. The NA1 lineage was the most common, occurring in seven retail nurseries, one wholesale nursery, one landscape situation, and both streams. The NA2 lineage was detected in three retail and one wholesale nursery, while the EU1 lineage was detected at a single wholesale nursery. At one nursery, both the NA1 and EU1 lineages were isolated from different branches on the same rhododendron plant. DNA fingerprinting identified six unique genotypes among the NA1 lineage isolates and two unique genotypes among the NA2 lineage isolates. High heterozygosity coupled with the clonal population structure, suggests that P. ramorum has not undergone sexual recombination in Washington state nurseries. High levels of genotypic diversity observed at three nurseries and lack of sexual recombination suggests multiple introduction events have occurred at Washington nurseries. The fingerprinting results have also provided some insights to potential sources of inoculum that infested the two streams. In one instance isolates obtained from an infested stream matched isolates associated with an infested nursery on the stream. However, in the other situation the isolate collected from an urban stream had a rare fingerprint and the source of the stream infestation is uncertain.
Increased sustainability of potato and verticillium control with green manures of corn
J. R. DAVIS (3), O. C. Huisman (2), D. T. Westermann (1), A. T. Schneider (3)
(1) USDA-ARS, Kimberly, ID, USA; (2) University of California, Berkeley, CA, USA; (3) University of Idaho, Aberdeen, ID, USA
Field studies involving 3 years of Russet Burbank potato showed that green manures of corn (Zea mays cv. Jubilee sweet corn) were effective for suppressing verticillium wilt caused by Verticillium dahliae Kleb. Further studies showed that once a suppressive effect had been established, a green manure treatment for a single season rather than 2–3 years of successive treatments were sufficient to either maintain or re-establish the control of verticillium wilt. Results also showed that with continued use of green manures, yields increased over time even though soilborne inoculum levels of V. dahliae had increased by >3-fold from 50 to 150 cfu per g of soil. Similarly, following 3 years of Russet Burbank potato, the wilt incidence became significantly lower even though soil inoculum levels had increased by >3-fold. Throughout the 3 years of potato cropping, the colonization of V. dahliae in potato stems was positively correlated with wilt incidence. Although there were highly significant increases of Pratylenchus spp. with the cropping of sweet corn, there was no indication of adverse effects as a result of this. Measurements of microbial activities in soil were shown to be negatively correlated with wilt incidence and V. dahliae root infections. When nutritional variables were taken into account, they were shown to be secondary towards relationships of cause and effect for disease suppression. Consistently fallow treatments showed lowest yields and significantly more wilt compared with green manure treatments. All data from this study showed Jubilee sweet corn to contribute positively to the sustainability of Russet Burbank potato while also providing a yearly crop of sweet corn between potato crops.
Relative roles of tuber and soil-borne inoculum in the development of Verticillium wilt in potato
J. K. Dung (1), D. A. Johnson (1)
(1) Washington State University, Pullman, WA, USA
Verticillium dahliae, the cause of Verticillium wilt (VW), persists for years in soil as microsclerotia and can be carried in the vascular tissue of potato tubers used for seed. The effects of soil-borne and tuber inoculum on VW symptoms were compared in the greenhouse. Naturally-infected and V. dahliae-free tubers were grown in V. dahliae-infested and non-infested potting mix. Area under the disease progress curves (AUDPC) were calculated from disease severity index ratings and stems and progeny tubers were assayed for V. dahliae. Mean AUDPC did not differ for infected and non-infected tubers grown in non-infested soils. Plants from infested soils had higher AUDPC than those from non-infested soil but mean AUDPC did not differ for plants from infected and non-infected tubers grown in infested soils. V. dahliae was isolated 30 cm up the stem from 96% of plants from infected and non-infected tubers grown in infested soils and 8% of plants from infected tubers grown in non-infested soil. Mean vertical microsclerotia colonization of stems was 50% total stem height for non-infected and infected tubers in infested soil and 0.5% for the infected tuber/non-infested soil treatment. V. dahliae was recovered from 15% of progeny tubers from plants grown in infested soil and 0% of progeny tubers from plants grown in non-infested soil. Tuber infection did not contribute to VW symptoms, indicating that efforts to reduce initial inoculum should focus on reducing the populations of the pathogen in the soil.
Evaluation of Thermal Pest Control technology for insect and disease control and harvest quality parameters in Romaine lettuce
J. J. FARRAR (1), A. B. Lawson (1)
(1) California State University, Fresno
Thermal Pest Control (TPC) uses a machine with a propane burner to force heated air onto plants as it is pulled through the field by a conventional tractor. Anecdotal evidence from Chile, Argentina, Brazil, New Zealand and Spain suggests that TPC can be substituted for traditional insecticide and fungicide applications for pest control and improves the quality of the harvested crop. In Romaine lettuce, TPC application every 7 days was compared with conventional insecticide and fungicide application and an untreated check for control of aphids and downy mildew and effect on harvest parameters. Harvest parameters included yield, tissue nutrient levels, and taste test. Incidence of downy mildew was low in all treatments on all ratings dates. Aphid populations remained low until just prior to harvest. Nutrient levels were similar among all treatments and there were no treatment differences in consumer preference according to the taste test. This was the first replicated field trial of TPC technology. TPC for pest control and crop quality needs further research prior to drawing well-supported conclusions.
Risk assessment of Verticillium wilt in organic production of strawberry in California
L. L. GALLEGOS (1), H. Su (1), W. Gubler (1)
(1) University of California, Davis
Verticillium wilt, caused by Verticillium dahliae Kleb., is a severe problem in organic strawberry production in California. This fungus overwinters in the form of microsclerotia which survive for many years in the soil and serve as a major source of inoculum for subsequent crops. Currently, the threshold for a high risk of Verticillium wilt in strawberry is based on growers’ experience and data gathered from other crops such as cotton. However, there has been no specific relationship determined for inoculum level of V. dahliae and effects on strawberry. A functional model for rapidly assessing the risk of the disease will allow growers to make informed, science-based decisions in order to minimize losses. To establish the relationship between inoculum and disease level, plots in fumigated commercial strawberry fields were artificially infested with microsclerotia of V. dahliae. Plots consisted of ten plants each, with six replications of eight inoculum levels (representing 0, 1, 3, 5, 10, 15, 20 and 30 microsclerotia per gram of soil), repeated at two separate sites. Soil samples were taken from each plot and plated on NP-10 media using the modified Anderson air sampler technique to quantify actual inoculum levels. Each plant was measured (height and width) and rated for disease severity at regular intervals throughout the harvest season to monitor disease progression. Marketable fruit yield was recorded at every harvest. Results show that as few as five V. dahliae microsclerotia per gram of soil are enough to cause significantly higher disease severity and have a significant impact on marketable yield, with an average of 24% reduction in yield compared to controls. Inoculum levels as low as three microsclerotia per gram of soil resulted in moderate disease severity, and ten or more microsclerotia per gram of soil resulted in yield losses of 47–63%.
Next steps on the horizon for weather and climate-based decision support systems
D. GENT (10), L. Coop (5), C. Daly (8), A. Fox (4), G. Grove (1), D. Gubler (2), P. Jepson (6), D. Johnson (3), W. Mahaffee (10), W. Pfender (10), J. Strand (9), C. Thomas (7)
(1) AgWeatherNet, Dept. Plant Pathology, Washington State University, Prosser, WA; (2) Dept. Plant Pathology, UC Davis, CA; (3) Dept. Plant Pathology, Washington State University, Pullman, WA; (4) Fox Weather, LLC, Fortuna, CA; (5) Integrated Plant Protection Center, Dept. Botany and Plant Pathology, Oregon State University, Corvallis, OR; (6) Integrated Plant Protection Center, Oregon State University, Corvallis, OR; (7) National Plant Diagnostic Network, Dept. Plant Pathology, UC Davis, CA; (8) PRISM Group, Dept. GeoSciences, Oregon State University, Corvallis, OR; (9) UC-IPM Program, UC Davis, CA; (10) USDA-ARS, and Dept. Botany and Plant Pathology, Oregon State University, Corvallis, OR
The Western Weather Workgroup is developing the conceptual, research, and implementation framework for weather information systems to support agricultural decision making and other societal purposes. Building on its current momentum, the workgroup seeks to expand its membership to encompass a broader geographic area and multi-disciplinary team. Objectives for the next three years include developing approaches to reduce known sources of uncertainties in weather-driven IPM decision-aids, refining site-specific estimated weather data and forecasts, and establishing linkages with national IPM decision support and biosecurity systems. Within three to six years, the workgroup aims to develop and deliver an operational system with downscaled, canopy-corrected estimated weather data. The system will include weather forecasts and links to pest model outputs. Central to achieving these objectives are distribution of products to IPM personnel and stakeholders, and identification of stable funding for long-term sustainability and system maintenance. Meeting these goals will enable integration of multiple systems nationally across diverse geographical and climatological regions, and provide opportunities for expansion into non-agricultural settings where site-specific weather and climate data currently are absent.
Sampling and detection based management of grapevine powdery mildew
G. G. GROVE (3), W. Mahaffee (1), L. Costadone (2)
(1) USDA-ARL HCRL, Corvallis, OR, USA; (2) WSU-IAREC, Prosser, WA, USA; (3) Washington State University Irrigated Agriculture Research and Extension Center, Prosser, WA, USA
A polymerase chain reaction (PCR) assay employing species-specific primers was developed to differentiate Erysiphe necator from other powdery mildews common in the northwest United States. During field studies, this PCR assay facilitated the detection of E. necator inoculum in air samples within hours of sample rod collection and prior to disease onset. The initial PCR detection of E. necator of the season occurred during seasonal ascospore releases caused by precipitation events between bud burst and the prebloom period during the three years of the study. Detection ceased for 7 to 11 days following ascospore release and then resumed several days prior to the observance of microscopic symptoms and signs of powdery mildew in the field. Results of this qualitative study were used to initiate fungicide programs in experimental and commercial vineyards and in both cases resulted in a reduction of fungicide usage and significant economic and environmental benefits.
Novel delivery IPM tools in real time for decision support - push
G. GROVE (1), C. Thomas (2)
(1) AgWeatherNet, Dept. Plant Pathology, Washington State University, Prosser, WA; (2) National Plant Diagnostic Network, Dept. Plant Pathology, UC Davis, CA
Washington State University’s AgWeatherNet (AWN) is a state-supported network comprised of about 100 regional weather stations and a support staff of 9 professionals. In addition to providing time-sensitive weather observations and raw data, AWN also has rapidly evolving internal and external value-added product portfolios that include insect models, disease models, water management tools, and cold hardiness information for perennial crops. Included in the external portfolios (powered by AgWeatherNet weather data) are commodity-specific decisions aids (http://das.wsu.edu), integrated production and business management software in production by the private sector (http://wine.tools4ag.net), and proprietary “internal” decision aids in development by the private sector. Both internal and external product portfolios include standard web-based delivery and but also utilize “push” technologies that include automated email and text messaging. A decision aid tool for wine grapes includes MS SharePoint UDAL (user defined alert layer) where the client can choose a variety of value-added products (e.g., mildew warnings, critical temperature, wind speed, or other weather parameter warnings, frost alerts, accumulated ET values, etc.) for delivery via email, text messaging, or synthesized voice at intervals specified by the subscriber.
Metabolites from Pseudomonas chlororaphis O6 differentially inhibit growth of Fusarium graminearum and Fusarium oxysporum
S. Han (2), J. Neisweinder (2), Y. Kim (1), A. Anderson (2)
(1) Chonnam National University Gwangju South Korea; (2) Utah State University, Logan, UT
Pseudomonas chlororaphis O6 suppresses growth of the wilt pathogen, Fusarium oxysporum f. sp. radicis-lycopersici, and fungi causing wheat and barley scab, F. graminearum. Metabolites produced by P. chlororaphis O6 that could be involved in fungal suppression include phenazines, hydrogen cyanide, siderophore, and pyrrolnitrin. To determine the effective compounds thin layer chromatographs of ethyl acetate extractions of secreted metabolites were overlaid with the fungi. F. graminearum was inhibited by pyrrolnitrin but both phenazines and pyrrolnitrin inhibited F. oxysporum. These results were supported by TLC bioassay of the extracts from the phzA mutant, which lacked production of phenazines, and the pyrrolnitrin-deficient prnA mutant. Production of these antimicrobial agents was sensitive to the nutrients supplied to the bacterium and required functional GacS and RpoS regulation. These factors may in part account for the variability of biocontrol under field conditions.
Control of seedborne Helminthosporium solani on specialty potatoes
D. INGLIS (3), P. Hamm (2), B. Gundersen (3), D. McMoran (4), N. David (1)
(1) NDSU, Fargo, ND; (2) OSU-HAREC, Hermiston, OR; (3) WSU-NWREC, Mt. Vernon, WA; (4) WSU/Skagit Co. Extension, Mt. Vernon, WA
Increasingly, silver scurf (SS)-infected seed lots are planted in rain-fed and semi-arid areas of the PNW. To determine whether seed fungicides control SS in contrasting environments, naturally-infected seed of Cascade White (CW), Chieftain (CH) and Yukon Gold (YG) were treated with 5 fungicides (fl oz/cwt) and planted near Mt. Vernon (NWREC) and Hermiston (HAREC). Checks included susceptible Russet Norkotah (RN); no seed treatment (nst); and, SS-free pre-nuclear seed (except YG). Field plots were planted in May in a split plot design with 4 reps, and maintained for 10 wk by typical practices. For each cultivar, emergence and yield among treatments was more uniform at NWREC (91–100%; 2.0–2.7 lb/plant) than at HAREC (49–97%; 3.5–6.0 lb/plant) despite planting the same seed lots. Following harvest, SS severity on NWREC tubers (2–34% surface w/lesions) was significantly reduced relative to nst for: Dynasty (.38) and Dynasty+Maxim (.38+.08 of D+M) on CW; all except Mertect (.021) on RN; and Maxim (.16), Dynasty, and D+M on YG. SS severity on HAREC tubers (0–3.3%) was significantly reduced due to Dynasty and D+M on RN, and for all except Maxim (.8) on YG. SS incidence in pre-nuclear seed treatments was unexpectedly high at NWREC (68–99% sporulating tubers) but low at HAREC (1–5%), suggesting infection in the field before harvest.
Survival of Colletotrichum acutatum on common strawberry nursery cover crops
J. R. JERTBERG (1), W. D. Gubler (1)
(1) Department of Plant Pathology, University of California, Davis, CA, USA
Strawberry anthracnose is a serious disease caused by Colletotrichum acutatum. Nursery transplants can carry inoculum and new transplants have developed symptoms in fruiting fields. At what point this fungal pathogen enters the nursery production system, and from what source, remain unclear. Volunteer strawberry plants in nursery rotation fields have been identified as sources of inoculum for infections occurring in adjacent fields. In addition, the rotation crop itself may provide a suitable substrate for survival and sporulation of the fungus, thus providing another source of inoculum. To better understand the disease cycle of C. acutatum on strawberry in California, common nursery cover crops including Austrian winter pea, bell bean, clover, hairy vetch, Merced rye, oats, Sudan grass, triticale, and wheat were evaluated for their role in the epidemiology of the disease. Additional species representing ten plant families were evaluated for their potential use as novel rotation crops. Strawberry (cv. ‘Albion’) was included as a positive control. Plants were inoculated with conidial suspensions in growth chambers. Isolations and sporulation assays showed the fungus is able to asymptomatically colonize all plant species tested, remain viable in dry plant debris for at least one month, and sporulate upon exposure to moisture, with significant differences among plant species. C. acutatum can be re-isolated from at least 80% of some crop tissues (e.g. sunn hemp, potato and wheat); while onion (13.2%), corn (16.7%), and bell bean (24.3%) are more difficult to re-isolate from. Sporulation assay results indicate the fungus can produce at least 7 × 10(^4) conidia/mg debris (dry weight) on plant species such as basil during one week at 100% RH. On other species, like tomato, significantly less sporulation was detected. These results suggest risk of C. acutatum inoculum propagation may be reduced in rotation fields by planting less-susceptible crops.
Strategies for controlling macadamia quick decline
L. M. KEITH (1), L. S. Sugiyama (1), M. A. Nagao (2)
(1) USDA-ARS, PBARC; (2) University of Hawaii
Quick decline of macadamia (Macadamia integrifolia) trees continues to be a serious problem in Hawaii. Initial signs and symptoms include bleeding, the presence of Ambrosia beetles and orange fruiting bodies of Nectria sp. followed by yellowing and browning of leaves within the tree canopy. Isolations from diseased branches have yielded Phytophthora capsici. A zoospore suspension of P. capsici was injected into branches of cultivar “HAES 344” to incite macadamia quick decline (MQD) signs and symptoms. Two branches showed for the first time MQD bleeding, powder posts and Nectria in an inoculation proving Koch’s postulates and also indicating that P. capsici may be the primary causal agent. Control methods for MQD with the fungicide Fosphite were investigated on the cultivar “HAES 333”. Soil drenching proved ineffective and was abandoned for a trunk injection method for delivering the fungicide. Initially, a passive trunk injection method was utilized. A 10 ml syringe containing concentrated Fosphite was used to dribble the fungicide into a 1½” deep hole that was drilled at a downward angle into the trunk of the tree. Unfortunately, only 25% to 50% of the label rate was applied. A more efficient and reproducible method utilized a pressurized injection system (Arborjet Tree I.V. System). With this system, the entire amount of fungicide was delivered into 12 trees at the label rate. The Fosphite control vs. no control field was monitored every two weeks for signs of MQD. MQD trees with no control died within an average of 205 days or 6.8 months after first signs of infection. Fosphite-treated trees have survived thus far for an average of 614 days. With treatment, trees to date have lived an additional 409 days. The trunk injection method may provide the macadamia industry a well needed control method for MQD.
Quantitative real-time PCR detects and quantifies colonization activity of Trichoderma spp.
T. Kim (1), G. R. KNUDSEN (1)
(1) University of Idaho, Moscow, ID, USA
Trichoderma spp. parasitize sclerotia and are potential biocontrol agents of Sclerotinia sclerotiorum. Traditional methods (plating, microscopy) to quantify growth and colonization by Trichoderma spp. in natural environments are labor-intensive, with limited resolution. Our objective was to develop quantitative real time PCR methods to detect and measure colonization of sclerotia by Trichoderma. Specific PCR primer/probe sets were developed for Trichoderma spp. and S. sclerotiorum. A total of 180 ITS1 (internal transcribed spacer) and ITS2 sequences from different Trichoderma species were aligned, and consensus sequences determined. Six candidate primer sets were based on conserved regions, and the specificity of each nucleotide sequence was examined using BLAST (Basic Local Alignment Search Tool). Primer sets were tested on genomic DNA of T. harzianum strain ThzID1-M3, six Trichoderma isolates from soil, and genomic DNA of S. sclerotiorum. The optimum primer/probe set (TGP4) successfully amplified genomic DNA of all Trichoderma isolates tested, showing high precision and reproducibility over a range of 8 orders of magnitude (85 ng - 8.5 fg of genomic DNA). TGP4 did not amplify S. sclerotiorum DNA. PCR primer/probe set TMSCL2 was developed for S. sclerotiorum, based on the calmodulin gene sequence. TMSCL2 did not amplify Trichoderma DNA. Quantitative real-time PCR with these primers was used in experiments to evaluate effects of two soil moisture levels (–50 kPa, –1000 kPa matric potential) on colonization of S. sclerotiorum by indigenous Trichoderma spp. Periodically over 40 days, Trichoderma and S. sclerotiorum DNA in sclerotia were quantified by PCR with appropriate primers. More than 90% of sclerotia were colonized by indigenous Trichoderma at 1000 kPa, vs. 60% at 50 kPa. Real-time PCR allowed measurement of the extent of colonization, which was significantly greater in the drier soil. This method provides a sensitive detection and measurement tool to evaluate colonization of sclerotia by Trichoderma spp.
Downy mildew resistance in four breeding lines of quinoa
L. KITZ (1), B. Geary (1), M. Stevens (1), G. Hooper (1)
(1) Brigham Young University, Provo, UT
Quinoa (Chenopodium quinoa Willd.) is a staple crop in the Andean highlands of South America exhibiting a high nutritional content and drought tolerance. The most significant disease of quinoa is downy mildew caused by the pathogen Peronospora farinosa f. sp. chenopodii Byford. It is endemic to Bolivia, Colombia, Ecuador, and Peru, and decreases yields by 33–58% and up to 99% in certain genotypes. The most effective means of managing downy mildew is through the development of resistant cultivars, as fungicides are expensive and difficult to obtain for subsistence quinoa growers. Genotypes KU2, 0654, NL6 and Chucapaca were grown under greenhouse conditions, inoculated and evaluated for disease resistance in a growth chamber. Genotypes 0654 and NL6 showed moderate levels of resistance, while Chucapaca showed high levels of susceptibility. Pathogen movement through host tissue of resistant and susceptible genotypes was also observed using scanning electron microscopy (SEM). Presence of the mildew was verified with amplification of the ITS region using PCR. SEM observation showed that sporangiophores create an appressorium, enter through stomata, colonize tissue intercellularly, and sporulate through stomata.
Overview of the Western IPM Weather Workgroup - Diverse collaboration to meet challenges
W. MAHAFFEE (9), D. Gent (9), L. Coop (5), C. Daly (7), A. Fox (4), G. Grove (1), D. Gubler (2), P. Jepsen (5), D. Johnson (3), P. Pfender (9), J. Strand (8), C. Thomas (6)
(1) AgWeatherNet, Dept. Plant Pathology, Washington State University; (2) Dept of Plant Pathology, UC Davis, CA; (3) Dept. of Plant Pathology, WSU, Pullman, WA; (4) Fox Weather, LLC, Fortuna, CA; (5) Integrated Plant Protection Center, Oregon State University; (6) NPDN, Dept of Plant Pathology, UC Davis, CA; (7) PRISM Group, Northwest Alliance for Computational Science & Engineering, Oregon State University; (8) UCIPM Program, UC Davis, CA; (9) USDA-ARS, Corvallis, OR
The Western IPM Weather Workgroup is a dynamic group of climatologist, meteorologists, entomologist, and plant pathologists from both the private and public sector who are actively engaged in the development and delivery of management tools that utilize weather and forecast data. The group grew from numerous individual efforts into a collaborative team due in part to funding from the CSREES Western IPM Program on workgroups. The group’s mission is to improve crop management decision-making abilities by developing new approaches to access, synthesize, distribute, and use weather data. There is an emphasis on integrating climatological and weather information to produce estimates of current and forecasted weather, and on approaches for delivering the information to decision-makers. In pursuit of this mission the group has identified impediments and potential solutions to the use of IPM tools reliant on access to weather data. We have sought funding for and initiated several research projects to test new approaches for spatializing weather and forecast data, with the goal of developing the methods for delivering estimated, site-specific weather and forecast data with a resolution of one km or less. We welcome collaborations with anyone having similar interests.
Virus complexes: Unraveling the mess and implications in disease management
R. R. MARTIN (1)
(1) USDA-ARS, HCRL, Corvallis, OR
Recent work with virus diseases of strawberries, raspberries and blackberries have shown that in most cases diseased plants in the field are infected with more than one virus and that many ‘severe’ strains of viruses in these crops are actually due to mixed infections. In these complexes, there are usually several viruses that are critical for disease development and there may be several that are not important in the disease. It is necessary to identify the viruses in the complex that are critical for the disease to develop. At least 13 viruses have been identified in blackberry plants exhibiting yellow vein symptoms and dieback. However, in any one area there is only a subset of these viruses present and a single virus, Blackberry yellow vein associated virus is always present. However, BYVaV is symptomless in single infections, as are many of the other viruses in the complex. The same is true for strawberries showing symptoms of decline, different complexes in different areas and most viruses symptomless in single infections. The key to control is to identify the viruses in the complex that contribute to the disease in the field and then determine which is the easiest to manage in that region. Virus management requires knowing the vector for each of the important viruses, something about the biology and ecology of the vector and the sources of inoculum for each of the viruses. Vector management is key for control of viruses in perennial crops. The application of molecular detection methods to the production of virus-free plants and to virus management in nurseries and fruit production fields will be discussed.
Effect of rootstock and lemon variety on development of brown wood rot by Antrodia sinuosa
M. E. MATHERON (1), M. Porchas (1)
(1) University of Arizona, Yuma, AZ, USA
In 1992 and 1997 respectively, Coniophora eremophila and Antrodia sinuosa were first reported to be associated with a brown heartwood rot occurring on lemon trees in Yuma, Arizona. Subsequent research revealed that the optimum temperature range for growth of both wood-rotting fungi was 30–35°C and development of wood decay columns was greatest from May through October. Also, the rate of wood decay caused by A. sinuosa was significantly higher than that caused by C. eremophila. In recent years, virtually all new occurrences of brown wood rot on lemon trees in Yuma are caused by A. sinuosa. To evaluate the possible effect of rootstock and lemon variety on the rate of development of brown wood rot caused by A. sinuosa, a planting of five different lemon varieties (Corona Foothills, Eureka, Frost, Limoneira 8A, and Prior) was established on three different rootstocks (Citrus jambhiri, C. macrophylla and C. volkameriana) in 2003. In July of 2006 and 2007, branches on these trees approximately 3 to 4 cm in diameter were inoculated by inserting a small wooden dowel colonized with the fungus into a hole drilled into each test branch. Inoculated branches were removed eight months later and the length of wood decay columns were measured. For all lemon varieties on C. macrophylla rootstock, the mean length of wood decay columns in the 2006 and 2007 trials was 12.7 and 9.2 cm respectively. These values were significantly greater than those recorded for lemon varieties on Citrus jambhiri (6.4 and 6.6 cm) and C. volkameriana (8.3 and 6.3 cm) during the same respective years. There were no consistent differences among the different lemon varieties in the rate of brown wood rot development in these two trials.
Examining the association between cold therapy of Pierce’s disease-infected grapevines and viability of cultured Xylella fastidiosa cells in vitro
M. M. MEYER (1), B. C. Kirkpatrick (1)
(1) University of California, Davis
Pierce’s Disease (PD)-infected vines can be cured of infection after exposure to cold temperatures; therefore PD does not occur in colder regions of North America. To better understand this phenomenon, PD disease severity, curing rates and biochemical changes in Pinot Noir (PN) and Cabernet Sauvignon (CS) grapevines grown in 4 field locations and in 4 cold chamber temperatures were compared to the viability of Xylella fastidiosa (Xf) cells cultured in vitro. Xf viability was evaluated in water, grapevine xylem sap, various media and buffers at different pH values. Xf cell suspensions were exposed to various temperatures between –20°C and 28°C. Viable colony forming units were counted daily for one week to determine the effect of each temperature treatment. Xf survival was best in PD3 medium compared to other buffers at temperatures between –5°C and 28°C. No culturable Xf was recovered from any of the media, buffers, xylem saps or water after 24 hours at –10°C or at –20°C. Differences between Xf viability en planta and in vitro were observed. PD severity was lowest and curing rates were highest for infected vines exposed to the coldest temperatures. Differences in Xf survival between the field and in culture suggest that cold curing is impacted by the physiology of the grapevine. The field collected xylem sap varied in pH from 5.5–6.2, whereas the buffer experiments show that Xf survives best at pH of 6.6–6.8. Osmolarity of PD3 media, used to grow Xf, is 113 mmol/kg, whereas the osmolarity of extracted xylem sap is 25–45 mmol/kg. Trends will be discussed as they relate to potential factors that mediate cold therapy.
Characterization of resistance to powdery mildew in grapevine progeny
F. MLIKOTA GABLER (1), D. A. Margosan (1), D. W. Ramming (1), J. L. Smilanick (1)
(1) USDA-ARS, Parlier, CA
The progeny of three sources of resistance to powdery mildew (PM), all backcrosses to Vitis vinifera were evaluated: Vitis romanetii; 2) Muscadinia rotundifolia; and 3) Vitis aestivalis. We evaluated PM prevalence and severity among segregants in the greenhouse and microscopically examined the resistance reactions. The progeny population of the V. romanetii backcross segregated into two main groups: highly resistant or highly susceptible to PM. The progeny of the V. aestivalis backcross and those of M. rotundifolia backcross segregated into many categories of resistance. Histological examination included segregants with various degrees of susceptibility to PM. Hydrogen peroxide (H(2)O(2)) accumulation, which is often associated with a signaling role in the cell to initiate secondary defense mechanisms including hypersensitive cell death, was evaluated 48 h after inoculation. Positive H(2)O(2) reactions were verified by diaminobenzidine stain. We identified three types of H(2)O(2) reactions in each segregant population: 1) localized (reaction was present in a small area just below appressorium); 2) moderate reaction (reaction extended beyond the appressorium area); and 3) whole-cell reaction (100% of the cell area was stained, often with several surrounding cells affected). Whole-cell reaction, which is the symptom of hypersensitive cell death, was rare and was identified only in a few cases in PM-susceptible and PM-resistant segregants. Spearman’s rho coefficient showed no correlation between PM susceptibility in the greenhouse and positive H(2)O(2) reactions, suggesting that in evaluated populations resistance to PM is conferred by some other mechanism.
Temporal and spatial effects of long-term floor management on the bacterial and nematode communities in a Salinas Valley, California grape vineyard
S. R. PARKER (2), D. A. Kluepfel (1)
(1) USDA-ARS, Davis, CA; (2) University of California, Davis
California grape producers traditionally manage vineyard floor vegetation to control weeds and vine vigor, and prevent erosion. The attitude towards vineyard floor management of some has changed from one of preventing disease and weeds to promoting plant and soil-borne microbial diversity. In the final year of a long term vineyard floor management field study, we examined both the bacterial and nematode communities present in the row middles and berms across six different floor management strategies. Samples were assayed for total bacterial and nematode populations in addition to identifying individual members of these communities. An analysis of the culturable bacteria community found weed management and cover cropping practices had no significant quantitative effect on bacterial populations. Qualitatively, however, bacterial populations were altered as a function of cover crop and weed management practices. The grapevine rhizosphere bacterial populations were greater than populations in the row middles bulk soil during the grape root flush in the spring. During harvest and dormancy, bulk soil bacterial populations were greater in the rows than on the berm (P < 0.05). The nematode community in the row middles was significantly affected by both weed management and cover crop practices. In the berm, nematodes were not affected quantitatively or qualitatively under the six management regimes. Moreover, the nematode community of the berm was different from that found in the row. These data suggest changes in the microbial community in the row do not influence the microbial community of the berm where the roots of the vine are concentrated.
Differences in plant defense gene expression during Fusarium crown rot infection in susceptible and partially-resistant wheat seedlings
J. E. PETRISKO (1), J. M. Windes (1)
(1) University of Idaho
Fusarium crown rot caused by F. culmorum remains a constant problem for dry land wheat production in Southeastern Idaho. We designed a laboratory study to investigate the genes involved in plant defense against F. culmorum infection in wheat seedlings of the partially-resistant Australian line ‘2-49’ and the susceptible wheat variety ‘Puseas’. A transcriptional analysis of both genotypes at 10 days post-inoculation with F. culmorum was done using the Affymetrix wheat gene chip. Five plant defense genes with differences in expression were chosen for further characterization at 1, 5, and 10 days post-inoculation using real-time quantitative RT-PCR. One–way ANOVAs were used to test pair-wise comparisons between 2-49 and Puseas for inoculated and non-inoculated treatments at each time point for each gene. The real-time quantitative RT-PCR analysis of plant defense genes chitinase 1, oxalate oxidase, WIR 1, stress-response protein, and xylosyltransferase showed that induction of chitinase 1 and WIR 1 occurred in the inoculated treatment of Puseas at 10 days post-inoculation. Oxalate oxidase was expressed at a higher overall level in 2-49 than in Puseas. Stress-response protein was expressed at a higher overall level in Puseas than 2-49. Xylosyltransferase showed significant induction in the inoculated treatment of 2-49 at 5 days post-inoculation. The differences in expression between the two genotypes showed that resistant and susceptible wheat seedlings have distinctly different genetic defense responses to F. culmorum infection. Further characterization of these genes and the pathways that they are involved in are needed to understand the mechanism of partial seedling resistance in wheat.
Uncertainties in modeling and weather estimation - Conceptually unique case studies
W. PFENDER (5), D. Gent (5), W. Mahaffee (5), A. Fox (2), L. Coop (3), C. Thomas (4), G. Grove (1)
(1) AgWeatherNet, Dept. Plant Pathology, Washington State University, Prosser, WA; (2) Fox Weather, LLC, Fortuna, CA; (3) Integrated Plant Protection Center, Dept. Botany and Plant Pathology, Oregon State University; (4) National Plant Diagnostic Network, Dept. Plant Pathology, UC Davis, CA; (5) USDA-ARS, and Dept. Botany and Plant Pathology, Oregon State University, Corvallis, OR
The output of a pest model decision aid is based on an interconnected chain of estimates and calculations, from weather element values through model inputs to model performance. Error, or uncertainty, in each step of the process affects the uncertainty of the final output. In order to prioritize efforts at improving accuracy of the final output, it is useful to know which steps are currently most in need of improvement, and how sensitive the final output is to error at each step. In field studies to partition this uncertainty, weather elements (e.g., temperature, leaf wetness) were measured at field locations in several crops and used to run various types of disease management models (e.g., simulation, disease warning index). We compared model outputs to those obtained by using estimated (rather than actual) weather data as model inputs, and compared both to observed levels of disease in the fields. In initial trials in 2007 we noted that temperature (e.g., daily max, min, average) was well portrayed by the weather estimation procedures (monthly average error < 1C), but moisture (e.g., precipitation and leaf wetness) estimates were subject to greater error. Weather estimation errors also were greater in some months of the year than others. Estimation of canopy-level weather elements (used for disease model inputs) from standard-height measurements was another source of error whose magnitude was affected by time of year. Effects of these errors on the management recommendations produced by disease models differed with the type of model. Uncertainties estimates and model performance for a stem rust simulation model and powdery mildew risk index are presented and discussed as conceptually unique case studies.
“Following the genes that make resistant plants: Shared tools for breeding and pathology”
G. RAUSCHER (1)
(1) USDA-ARS, Salinas, CA
Although plant pathology and breeding are distinct disciplines with unique perspectives, they frequently share a common goal: that of identifying and understanding durable resistance, the kind of resistance that will not be overcome quickly and will remain effective against a wide array of isolates. While pathologists strive to discover the sources of resistance, it is the breeder’s function to deploy and make them useful to the agricultural community. This function has become of paramount importance for improving the productivity and sustainability of agriculture and reducing its environmental impact. Two of the main challenges breeders face are time and diversity. Crop variety development is a lengthy process; it may take up to 20 years to introgress a single gene into a commercial variety. The limited durability of most R-genes makes it even more important to identify and deploy new sources of resistance rapidly. Pathogen diversity also plays a major role in plant breeding. In pathosystems with a wide array of isolates, or subject to fast pathogen evolution, the deployment of single resistance genes may not be as functional as the use of multilines or pyramiding genes. The identification of the correct phenotypes is crucial during the breeding process, but it can be difficult and time consuming, especially when desirable and detrimental genes are linked. However, the use of molecular markers such as AFLPs, RFLPs, SSRs and SNPs can accelerate the process of surveying the genome for the correct array of resistance genes in a breeding progeny, making it more efficient than the traditional method of inoculation for phenotyping and substantially shortening the breeding time. Molecular markers have become increasingly popular in the search for major R-genes, QTLs and even those genes involved in resistance pathways. To date, a wide array of major R-genes have been mapped, characterized and cloned. Structural similarities between R-genes have allowed for identification of resistance clusters, making it easier to recognize areas of the genome desirable for breeding. This, in turn, has the potential to enhance the durability of resistance as it has been shown that linked R-genes tend to act synergistically. Furthermore, when resistance clusters are mapped in model pathosystems, synthenic areas can reveal the location of resistance in related species, giving clues of chromosomal segments that may be important to explore for breeding.
Ringspot leaf symptoms on Sorbus scopulina Greene associated with virus-like particles
N. L. ROBERTSON (1), K. L. Brown (1)
(1) USDA, ARS, Palmer, AK, USA
Sorbus scopulina Greene (Greene’s mountain ash), is a native shrub of Alaska that is widely distributed in south central Alaska in natural ecosystems and as an ornamental in public and residential landscapes. In spring, emerging leaves frequently contain noticeable chlorotic ring spots, vein-clearing that often develop into oak-leaf patterns. Erinea and gall forming eriophyid mites were often present on leaves of affected plants. Ultra-thin sections of leaf mesophyll revealed single to several spherical structures (average diameter 50 nm) enclosed within a membrane. Amorphous inclusions similar to viroplasm-like structures were readily visible. Although particles were not detected from purified “virus” preparations, a prominent protein ~32 kDA was consistently present from only symptomatic leaves. The 32 kDa protein did not have a serological affinity with universal potyvirus antiserum or with European mountain ash ringspot-associated virus antiserum on western blots. Double-stranded RNA and “virion” RNA extraction procedures did not result in distinct bands on agarose gels, and may have been precluded by interfering leaf polysaccarides and tannins. Polymerase chain reaction using universal potyvirus primers and cDNA from total RNA extracts did not generate products with distinct bands. Symptoms and the associated 32 kDa protein were not detected on the following plants that had been inoculated with sap from affected leaves: Sorbus scopulina, S. aucuparia, Nicotiana benthamiana, Chenopodium amaranticolor, and C. quinoa. The presence of a 32 kDa protein, membrane bound spherical particles, chlorotic leaf symptoms, an association with eriophyid mites, and difficulties with nucleic acid identity, suggests that the causal agent of diseased S. scopulina Greene is similar to a group of unclassified tentative viruses with a unique morphology of membrane bound particles.
Application of real-time PCR for quantification of soilborne pathogens
K. L. SCHROEDER (1), P. A. Okubara (1), T. C. Paulitz (1)
(1) USDA-ARS, Root Disease & Biological Control Research Unit, Pullman, WA
Soilborne pathogens can be particularly difficult to quantify. Unlike foliar diseases, symptoms caused by soilborne pathogens such as Pythium and Rhizoctonia spp. are not readily observable, making it difficult to estimate pathogen populations. Pythium and Rhizoctonia present an additional problem in cereal production systems. Rather than the diseases being caused by a single species of each genus, multiple species may be present in the same field and even on the same plant. In eastern Washington, the species prevalence and diversity of each of these pathogens can vary greatly from one region to another. Due to limitations of traditional agar media-based quantification methods, real-time PCR assays were developed for multiple species of Pythium and Rhizoctonia. Soils were collected over a large geographic region of eastern Washington in 2005, 2006, and 2007. Total DNA was extracted from these soils and species-specific primers for three species of Rhizoctonia and three to nine species of Pythium were used with a Roche LightCycler to quantify pathogen DNA in these soils. The prevalence of Pythium species is favored by higher precipitation zones. The diversity can also very greatly with as many as nine or as few as one species being detected in a single soil sample. Conversely, R. solani AG-8 is quantified in low amounts in the higher precipitation zones and favors areas with less than 300 mm of annual precipitation. Rhizoctonia oryzae is less affected by precipitation, being prevalent in most regions. This work has also revealed correlations between the presence of certain species of these necrotrophic root pathogens with specific host plants. For example, R. solani AG-2-1 is favored by rotations with brassica crops. Using these real-time PCR assays, disease risk models are being created to develop this procedure into a preplant tool for improved disease management.
Effect of 1-Methylcyclopropene (1-MCP) on reducing postharvest decay of tomatoes
H. SU (1), D. Gubler (1)
(1) Department of Plant Pathology, University of California, Davis
1-Methylcyclopropene (1-MCP), which is marketed as SmartFresh™ technology, is an ethylene antagonist and has been shown to delay ripening in tomatoes. We evaluated 1-MCP for its efficacy at reducing tomato decay caused by Alternaria alternata, Botrytis cinerea, and Fusarium spp. on tomato cvs Quality 33 and Seminis 35. 1-MCP was applied at two rates (600 ppb for 12 h and 1000 ppb for 6 h) on tomatoes with or without artificial inoculation of Alternaria alternata and Botrytis cinerea. Fusarium rot occurred from natural inoculum. Postharvest decay was evaluated in 1-MCP treated and untreated tomatoes at 7–10 day interval for 31 to 42 days during storage at 15°C. The test was repeated twice on each cultivar at green or pink developmental stages. No differences existed in cumulative disease incidence or severity between treatments of 600 ppb and 1000 ppb 1-MCP, with or without inoculation of the pathogens. Cumulative incidence and severity of decay in 1-MCP treated tomatoes was significantly reduced compared to that of the corresponding controls for both cultivars. Disease incidence and severity of individual diseases in 1-MCP treated fruits was also significantly reduced compared to that of the untreated controls, except in one inoculated test where severity of Alternaria rot in 1000 ppb treated fruits were significantly higher after extended storage of 42 days, while incidence was significantly lower than its corresponding control. In two tests, either inoculated or non-inoculated, incidence of Alternaria rot was significantly higher in 1000 ppb treated fruits than that treated with 600 ppb. Our results indicate that 1-MCP can reduce postharvest decay in tomatoes.
Detection of Xanthomonas hortorum pv. carotae on and in carrot with loop-mediated isothermal amplification (LAMP)
T. N. TEMPLE (1), K. B. Johnson (1)
(1) Oregon State University
Detection of chromosomal DNA of Xanthomonas hortorum pv. carotae (Xhc) by a loop-mediated isothermal amplification protocol (LAMP) was evaluated in laboratory and greenhouse assays on carrot plants and seed. LAMP amplifies target DNA rapidly (1 hour), isothermally (65°C), and with high-specificity based on four primers designed to recognize six independent sequences of target DNA. A positive reaction results in a cloudy white precipitate of magnesium pyrophosphate in a PCR tube. With whole cell suspensions, our LAMP protocol had a detection limit of 5 to 25 colony forming units, which is similar to the sensitivity of nested PCR. The LAMP primers did not react with suspensions of other bacteria obtained from seeds or whole carrot plants at densities ranging from 10(^3) to 10(^7) CFU/g. In experiments with whole carrot plants, inoculation with a rifampicin resistant selection of Xhc at 3 × 10(^3) CFU/ml resulted in positive detection over a 4 week sampling period from symptomless plants. LAMP reactions on extracted DNA from commercial seed sample washes resulted in 100% detection for infested seed (ranging from 10(^4) to 10(^6) CFU/g) and 0% detection on seed not infested with Xhc. Overall, detection of Xhc on plants or carrot seeds using LAMP technology has the potential for enhancing management of this disease in the field.
Fremont cottonwood dieback in California caused by Cryptosphaeria species
F. TROUILLAS (1), W. Gubler (1)
(1) University of California, Davis
In 2005, we detected severe limb and twig dieback of Fremont cottonwood trees (Populus fremontii) in several counties in California including Napa, Sonoma, Solano, Merced, Sacramento, Yolo, Stanislaus and El Dorado. Symptoms in the wood consisted of brown discoloration and decay in both sapwood and heartwood. Symptoms were often associated with the presence of fungal fruiting bodies originating from the surface of dead bark. Occasionally the disease or the fungus was observed on additional cottonwood species including P. nigra and P. deltoides. Isolations from cankers and preliminary diagnostic work allowed us to recognize a new Cryptosphaeria species associated with the disease. Perithecia of this fungus were typical of Diatrypaceae, ascospores were brown, slightly curved, 12–16(–18) × 4.5–5 µm. Colonies had irregular margins, slow growth and color varied from orange to yellow on PDA. The anamorph resembled the form-genus Cytospora Ehrenb.:Fr. However, California isolates could be distinguished from the formerly documented C. chrysosperma by having longer conidia, (7.5–)10–16(–18) × 2–2.5 µm and representing a separate phylogenetic lineage. Phylogenetic analyses using ITS region showed that most Cryptosphaeria isolates from California formed a unique clade, which separated from all previously described Cryptosphaeria spp. Results of one year pathogenicity test showed that each of two Cryptosphaeria spp. tested were pathogenic to Fremont cottonwood. Fungi were recovered from all inoculated saplings after one year incubation period. Cankers developed in the wood and the extent of cankers varied from 50 to 63 mm for the various isolates, canker length in the control was only 22 mm. Taxonomy of Cryptosphaeria species occurring in California remains unclear and more work has to be done to fully characterize all putative fungal species. Work also is continuing to clarify fungi biology and disease cycle.
Double pruning as a potential method to control Bot canker disease of grapes and duration of susceptibility of grapevine pruning wounds to infection by Botryosphaeriaceae
J. URBEZ-TORRES (1), W. D. Gubler (1)
(1) University of California, Davis, CA, USA
Grapevine canker diseases, resulting from infected pruning wounds, are one of the main factors limiting vineyard longevity and productivity. Consequently, knowledge of low risk infection periods and pruning wound susceptibility are critical in deciding appropriate timing for pruning and wound treatment. Bot canker disease, caused by at least 9 different Botryosphaeriaceae species, has been recently identified as the most common canker disease in California vineyards. Double pruning of grapevines, which allows for more final pruning in late winter, has been shown to reduce infections caused by Eutypa lata, the causal agent of Eutypa dieback, because infections on prepruning wounds do not develop further than the final pruning point. In this study we evaluated the efficacy of double pruning to reduce infections caused by Botryosphaeriaceae species, a much more rapidly colonizing fungus than E. lata. Chardonnay and Cabernet Sauvignon grapevines were prepruned and separately inoculated with a spore suspension of Lasiodiplodia theobromae and Neofusicoccum parvum from mid October to February with a final pruning in March. Pruned-off canes were examined and length of vascular discoloration measured from the point of infection in order to determine whether fungal infection developed beyond the point of final pruning. Duration of susceptibility of pruning wounds to infection by Botryosphaeriaceae was studied in the same site. Vines were pruned from mid November to February and inoculated with the same fungal species at 12 day intervals after pruning during 50 days. Percentage of infected pruning wounds for each treatment was determined by isolation of the pathogens from necrotic margins of cankers and/or vascular discoloration. Results from both double pruning and grapevine pruning wound susceptibility to infection by Botryosphaeriaceae experiments will be presented and discussed at the meeting.
Characterization of broad spectrum Potato virus Y resistance in an Solanum tuberosum ssp. andigena-derived population and select breeding clones using molecular markers, grafting, and field inoculations
J. L. Whitworth (1), R. G. Novy (1), D. G. Hall (1), J. M. Crosslin (2), C. R. Brown (2)
(1) USDA-ARS, Aberdeen, ID, USA; (2) USDA-ARS, Prosser, WA, USA
Potato virus Y (PVY) causes yield loss in potato and PVY necrotic strains can cause potato tuber necrotic ringspot disease (PTRND) resulting in quality loss. Breeding for resistance to PVY can be achieved by incorporating the Ryadg gene from Solanum tuberosum ssp. andigena. Resistance obtained from the Ryadg gene has been shown to provide extreme resistance, defined as resistance to all strains. Past work in Europe has shown that Ryadg-based resistance has conferred resistance to PVYO and PVYN/NTN strains, but the resistance has not been tested against a new strain, PVYN:O, detected in North America. Molecular markers tightly linked to Ryadg have been developed and are being utilized for marker assisted selection (MAS) in potato breeding. Three molecular markers linked to Ryadg were used to screen a NY241-7 (PVY resistant) × GemStar Russet (PVY susceptible) breeding population and a set of 53 clones/cultivars in the USDA-ARS Aberdeen Potato Breeding program. The breeding population was mechanically and graft inoculated with three isolates each of PVYNTN, PVYN:O, and two PVYO isolates Results show a 1:1 segregation ratio of resistant to susceptible confirming that PVY-resistant parent, NY241-7, is simplex for Ryadg. Resistant progenies were resistant to all PVY strains and had the presence of markers linked to Ryadg whereas susceptible progenies were lacking the diagnostic markers. Use of the markers on the set of clones/cultivars shows that when positive results were obtained from all three markers, resistance was present, but differences between markers were noted in four resistant clones, three of which have S. stoloniferum background and one which has S. t. ssp. andigena background. Use of these markers shows that while some discrepancies exist, they are useful in MAS for PVY resistance against all PVY strains and their use can increase the selection efficiency for PVY resistance in breeding programs.
Residual effects of fludioxonil and pyrimethanil on blue mold in Red Delicious apple fruit
C. XIAO (1), R. J. Boal (1)
(1) Department of Plant Pathology, Washington State University, Tree Fruit Research and Extension Center
Fludioxonil and pyrimethanil are reduced-risk fungicides and were recently registered for postharvest use on pome fruits. Blue mold caused by Penicillium expansum is a common postharvest disease of apples. In 2005–06 and 2006–07 seasons, we investigated residual activity of fludioxonil and pyrimethanil in apple fruit against P. expansum. Organic Red Delicious fruit harvested from a commercial orchard were either not treated or drenched with fludioxonil, pyrimethanil, or thiabendazole at the label rates prior to storage and then stored in controlled atmosphere at 0°C for 5 and 7 months, after which time the fruit were removed from storage and subjected to washing and brushing during packing. Fruit were then wounded and inoculated with conidial suspensions of P. expansum. Inoculated fruit were treated either with sterile water or fungicides. Fruit were stored at 0°C for 8 weeks and at room temperature for one additional week after cold storage. During the 2-year study, no decay or up to 26% blue mold incidence was observed on fludioxonil-drenched fruit that were not treated with fungicides at packing. No decay or less than 4% blue mold incidence was observed on pyrimethanil-drenched fruit that were not treated with fungicides at packing, whereas 65–99% blue mold incidence was observed on thiabendazole-drenched fruit that were not treated with fungicides at packing. The results indicate that residual effects of fludioxonil and pyrimethanil applied prior to storage on blue mold in Red Delicious fruit can last for at least 7 months under apple-storage conditions.
Surfactants for crown gall management in walnut nurseries: Efficacy of benzalkonium chloride and cetyl trimethylammonium bromide on grafting tools
L. E. YAKABE (2), S. R. Parker (2), D. A. Kluepfel (1)
(1) USDA-ARS; (2) University of California, Davis
The dominant rootstock in California walnut production is Paradox (Juglans regia × J. hindsii). This rootstock is precocious, hardy in marginal soils, and resistant to Phytophthora diseases, although highly susceptible to crown gall caused by Agrobacterium tumefaciens. Recently, serious outbreaks of crown gall have occurred in walnut nurseries with crop losses approaching 100%. Galls are not only appearing on roots and crowns, but also at grafting and bleeding wounds made during the grafting process. In greenhouse trials, A. tumefaciens was readily transmitted from plant to plant via sequential wounding of Datura stramonium plants with a cutting tool. To investigate sanitizing options, A. tumefaciens was challenged by two cationic surfactants, benzalkonium chloride (BC) and cetyl trimethylammonium bromide (CTAB). After a 30 minute exposure, 5 ppm of BC or CTAB is required for 100% bacterial mortality of an aqueous suspension of A. tumefaciens. When compared to quaternary ammonium and sodium hypochlorite, both surfactants were less affected by organic matter and less corrosive to metal tools. These characteristics, along with low phytotoxicity, make BC and CTAB promising materials for use in most systems where pruning or grafting tools are potential inoculum vectors.