Posted online May 2, 2007
Investigating genetic diversity of Anisogramma anomala, causal agent of eastern filbert blight. S. N. BAXER (1), J. A. Crouch (1), R. F. Sullivan (2), B. I. Hillman (1), T. J. Molnar (1), and C. R. Funk (1). (1) Dept. of Plant Biology and Pathology, Rutgers University, New Brunswick, NJ 08901; (2) Center for Science and Technology Education, Kean University, Union, NJ 07083.
The fungal pathogen Anisogramma anomala, causal agent of the disease eastern filbert blight (EFB), appears endophytic in its growth habit with little influence on the American hazelnut (Corylus americana). In contrast, A. anomala is extremely pathogenic and destructive on the introduced European hazelnut (C. avellana), the commercial hazelnut. Based on data from our greenhouse inoculation trials, some isolates of the fungus appear more pathogenic than others. By sequencing the 28S region of the ribosomal large subunit we were able to place A. anomala in the Gnomoniaceae family, along with other pathogens such as Discula destructiva and Gnomonia leptostyla. We are currently exploring genetic variability within and between populations of this fungus, using nucleotide sequence data. We present the recent results of partial gene sequences from a calmodulin gene and beta-tubulin gene which were used to construct a phylogenetic analysis of A. anomala.
Evaluation of brown patch resistance in colonial bentgrass. S. A. BONOS and E. Weibel. Department of Plant Biology and Pathology, Rutgers University, New Brunswick, NJ 08901.
Brown patch, caused by the fungus Rhizoctonia solani, is one of the biggest limitations to the wide-spread use of colonial bentgrass (Agrostis capillaris) for fairways in the temperate US. The objectives of this study were to determine the inheritance of brown patch resistance in colonial bentgrass from controlled crosses between tolerant and susceptible bentgrass clones. Inheritance characteristics such as the detection of major genes, heterosis, and maternal effects were determined by evaluating the disease severity of parents and progeny from these controlled crosses. Parental clones and progenies from crosses were established in a field trial in a randomized complete block design with four replications and inoculated with one isolate of R. solani applied at a rate of 0.25 g/m(^2) of prepared inoculum. Significant differences were observed between parental clones and progenies. This research will be important for future breeding efforts in colonial bentgrass and could improve the utilization of this species for turfgrass situations.
Effect of QoI fungicide rate and time of inoculation on brown rot lesion development on peach fruit. A. BURNETT and N. Lalancette. Rutgers University, AREC, Bridgeton, NJ 08302.
The QoI fungicides azoxystrobin (Abound) and trifloxystrobin (Flint) were studied for their curative activity against Monilinia fructicola, causal agent of brown rot, during 2006. Fungicide treatments were applied to ‘Suncrest’ peach trees arranged in a RCBD with four replicates. During the fruit ripening period, each fungicide was applied at the maximum label rate and twice that rate. Attached fruit were inoculated at 1 day and 7 days after fungicide application; non-treated inoculated fruit acted as controls. Diameters of lesion and sporulating areas were recorded at five and seven days post inoculation. In the ANOVA, the fungicide main effect was significant (P < 0.0001). Abound and Flint significantly reduced lesion area by 36% and 20%, and sporulating area by 59% and 89%, respectively. No significant differences in either lesion or sporulating areas were found between rates. The inoculation timing main effect showed only a significant decrease in lesion area by the one day inoculation. Results indicate that QoI fungicides may help reduce disease pressure by reducing inoculum potential.
Spatial heterogeneity of apple scab, incidence-lesion density relationships and development of a sequential sampling plan. O. CARISSE, C. Meloche, G. Boivin, and T. Jobin. Agriculture and Agri-Food Canada, 430 Gouin, St-Jean-sur-Richelieu, QC, Canada, J3B 3E6.
Incidence is generally easier and faster to measure than severity which is often a more accurate estimation of disease progress. We studied spatial heterogeneity of scab incidence and lesion and established the incidence-lesion density relationships with the goal of finding a simple relationship for predicting disease intensity using either leaf or shoot incidence. From these analyses, a sequential sampling plan (SSP) that can be used to estimate the need for summer fungicide sprays was developed. Results showed that scab incidence was randomly distributed and that it was possible to develop an incidence-lesion density model. The SSP was developed from 129 data sets. The upper and lower acceptance limits were calculated with a threshold of 0.05 scabbed leaves per shoot. In 86.5% of the simulations, the SSP provided the appropriate answer, while in 2.6 and 3.4% of the simulations the SSP indicated that the orchard was below or above the threshold when the mean number scabbed leaves per shoot was above or below the threshold, respectively.
Effect of early-spring-pruning and copper sprays for managing bacterial canker of sweet cherry. J. CARROLL (1), T. Robinson (2), and T. Burr (3). (1) NYS IPM, (2) Dept. Hort. Sciences, (1,3) Dept. Plant Pathology, Cornell Univ., 630 W. North St., Geneva, NY 14456.
Bacterial canker is a serious disease of sweet cherry that limits tree life. The effects of leaving a 15-cm stub during pruning, coupled with pre- and post-pruning copper sprays, on canker control were evaluated. Three blocks of cv Hedelfingen on 3 rootstocks trained to a Vertical Axis, were used. Two branches per tree were pruned and the pruned zone on one of the branches was shielded from copper sprays by wrapping with plastic. The fate of Pseudomonas syringae pv. syringae (Pss) inoculated (3.4 × 10(^8) cfu/ml) on stub and flush pruning wounds that were treated and untreated with copper, as described, was assessed. During the growing season, pruned branches were rated for gummosis and extent of canker. Treatment with copper did not reduce gummosis, canker or fate of Pss. Both inoculated stubs and flush cuts developed bacterial canker and Pss was recovered from 94% and 97%, respectively. Results suggest copper sprays and stubs may not affect infection by Pss. Further research is required to determine the strategy’s effectiveness on long-term management of the disease.
Timing and movement of conidia of Zygophiala jamaicensis relative to flyspeck incidence in commercial apple orchards. D. R. COOLEY and A. F. Tuttle. Dept. of Plant, Soil & Insect Sciences, University of Massachusetts, Amherst, MA 01003.
Flyspeck of apple is an increasing problem on commercial apples in the Northeast, requiring significant applications of fungicide. In an attempt to better understand the epidemiology of flyspeck, conidia of the putative causal organism, Zygophiala jamaicensis, were trapped during several growing seasons at different locations within and adjacent to commercial apple orchards. Based on earlier studies of ascospore development, we hypothesize flyspeck infections on fruit are caused by conidia that are produced on reservoir hosts adjacent to orchards. This study examined the relative numbers of conidia trapped at varying distances from the orchard borders, at the timing of conidial production and at flyspeck development on apple trees relative to the spore captures. It indicated that both the number of spores captured and flyspeck incidence decrease with distance from the reservoir hosts. In addition, conidial release generally begins after ascospores have all matured and released, and continues through until the first frost.
Transposons and sex: What do they mean for Colletotrichum cereale? J. A. CROUCH, B. B. Clarke, and B. I. Hillman. Rutgers University, New Brunswick, NJ 08901.
Although sex is universal in all eukaryotic kingdoms, for the fungi, meiosis is often facultative. In populations of the fungus Colletotrichum cereale, which has recently emerged as a pathogen of cool-season turfgrasses, the prevailing mode of reproduction is thought to occur clonally, as inferred primarily through the lack of a teleomorph. Because a pathogen’s mode of reproduction strongly influences the course of its evolution, we are critically evaluating the hypothesized non-recombining nature of C. cereale populations. By investigating 3 transposon species as molecular markers in conjunction with multi-locus phylogenetic analysis, we have found evidence of recombination in this species. Furthermore, 21 of 36 unique transposon loci displayed the signature pattern of recurring rounds of repeat-induced point mutation (RIP), a genome defense mechanism that functions only during meiosis. Our work rejects the presumption of clonality for C. cereale and, given the severe economic losses sustained in turfgrass systems due to this pathogen, strongly emphasizes the need for additional inquiry into the biology, mating, and dispersal mechanisms of C. cereale.
An additional host and management tools for downy mildew of coleus. M. L. DAUGHTREY and M. Tobiasz. Dept. of Plant Pathology, Cornell University, L. I. Hort. Res. and Ext. Center, Riverhead, NY 11901.
A downy mildew disease due to a new Peronospora sp. caused crop losses and poor garden performance for coleus throughout the US in 2005-06. Sporulation was associated with leaf spots, flecks, curl, and abscission. Thus far, 11 seed-propagated cultivars and 26 vegetatively-propagated cultivars of coleus have been found to be susceptible by inoculating plants with conidia rinsed from infected coleus leaves and incubating them under high humidity. Two cultivars of anise hyssop (Agastache hybrids) also developed leaf spots with sporulation after conidial inoculation. Sprays of dimethomorph or fenamidone applied 24 hrs before inoculation entirely suppressed symptom development in coleus. Symptom incidence was decreased by mefenoxam drenches or foliar sprays with mancozeb plus spreader-sticker or azoxystrobin. Etridiazole, fluoxystrobin, fosetyl-Al, phosphite and trifloxystrobin treatments tested did not significantly reduce symptoms. Cultivar choice, humidity reduction, and use of effective systemic and contact fungicides in rotation will be helpful for managing downy mildew on coleus.
Evaluation of biopesticides for managing powdery mildew on pumpkin. J. F. DAVEY and M. T. McGrath. Dept. Plant Pathology, Cornell University, Riverhead, NY 11901.
Powdery mildew caused by Podosphaera xanthii is an annual production problem for pumpkin growers in most parts of the world causing loss of yield and fruit quality. An experiment was conducted in 2004, 2005, and 2006 to determine efficacy of several EPA-classified biopesticides and other products considered less toxic than conventional fungicides, many OMRI listed and some exempt from EPA registration, along with conventional grower standards. Active ingredients of materials tested included several oils (jojoba, sesame, fish, wintergreen, neem, cottonseed, corn, thyme, and mineral oils) garlic extract, hydrogen dioxide, potassium bicarbonate, sodium tetraborohydrate decahydrate, citric acid, capsaisin, Bacillus pumilius GB34, and Streptomyces lydicus WYEC 108. Most products were applied weekly with a tractor sprayer at the IPM threshold of one leaf out of fifty infected. All treatments provided some suppression of powdery mildew. Most effective products controlled powdery mildew at the same statistical level as the conventional grower standards Microthiol Dispers (sulfur) and Bravo Ultrex (chlorothalonil).
Fusarium species associated with declining Spartina spp. in areas affected by sudden wetland dieback. W. H. ELMER (1), C. L. Robertson (2), S. Useman (2), R. L. Schneider (2), and K. O’Donnell (3). (1) The Connecticut Agr. Exp. Sta., New Haven, CT 06511; (2) Dept. of Plant Path. & Crop Physiol, LA State Univ. Agr. Center, Baton Rouge, LA 70803; (3) NCAUR, ARS, USDA, Peoria, IL 61604.
Sudden wetland dieback (SWD) is characterized as a rapid death of wetland Spartina spp. Affected and unaffected plants from SWD sites and plants from areas where no SWD occurs in CT, LA, MA, and ME were sampled. Isolations from roots, crown and leaves yielded colonies of Fusarium more frequently from affected plants in SWD sites than unaffected plants. No Fusarium was recovered from Spartina spp. in New England sites where SWD did not occur. Amplification of the elongation factor alpha gene revealed an undescribed species among the LA isolates, shown to belong to the African clade of Gibberella fujikuroi. This species may have been introduced to North America. New England isolates were distinctly different from LA isolates and represented new species that belong to the trichothecene-producing clade of Fusarium. Pathogenicity tests have shown that these species are capable of inciting lesions on the plant; however, their role in SWD is not known.
Crop growth, ontogenic resistance and disease progress: A discussion with examples. F. J. FERRANDINO. The Connecticut Agr. Exp. Sta., New Haven, CT 06511.
Much attention has been directed to the effect of pathogen phenology on the time course of the resultant plant disease epidemic. Thus, the effects of latent and infectious time periods on the disease progress curve have been well studied. However, the time scale for increases in the leaf area and phenology of field crops is comparable to the time scale of epidemics. This simultaneous growth and development of host and pathogen has many ramifications on the mechanics of disease development. Disease assessment is often performed pro rata (per unit leaf area), so that crop growth dilutes the estimated apparent disease. Host density directly affects the probability of new infections (more leaves catch more spores or more roots sample more soil). When susceptibility to disease is dependent on the age of host tissue, the time course of crop growth determines the amount of potential infection sites available. Lastly, leaf area density and presentiment affect the microclimate of the canopy which alters spore survivability and overall infectivity. The manner by which all of these factors influence plant disease development is discussed.
Incidence and severity of bacterial leaf scorch of oak in the New Jersey urban forest. A. B. GOULD (1), G. Hamilton (2), M. Vodak (3), J. Grabosky (3), H. Staniszewska (1), and J. Lashomb (2). (1) Dept. Plant Biology and Pathology; (2) Dept. Entomology; and (3) Dept. Ecology, Evolution, and Natural Resources, Rutgers University, New Brunswick, NJ.
Bacterial leaf scorch (BLS) of oak has reached epidemic proportions in certain central and southern New Jersey locations. The disease, caused by the xylem-limited bacterium Xylella fastidiosa, affects trees in the red oak group in urban communities and parks. The incidence of BLS of oak in several New Jersey municipalities was assessed in ground surveys conducted from 2002 to 2006. At the end of the survey period, disease incidence in a severely affected Monmouth County community approximated 45%. Although disease incidence in two other communities was lower (an average of 15 or 30%), BLS still affected a sizeable portion of the oak street tree resource. In most surveys, average crown dieback of symptomatic oaks was between 15 and 30%. With rare exceptions, all other shade tree species examined during the survey appeared to be free of the disease.
Control of Pythium root rot of greenhouse tomato: A microbial approach. V. GRAVEL, H. Antoun, and R. J. Tweddell. Centre de Recherche en Horticulture, Université Laval, Québec, QC, Canada G1K 7P4.
Control of Pythium root rot (Pythium ultimum Trow) of tomato grown in hydroponic systems is an important problem due to the lack of effective methods. As part of a research program aimed to develop a biological control strategy, a selection process allowed identification of 40 microorganisms which displayed a strong antagonistic activity in vitro against Pythium ultimum. Among these, 8 (Penicillium brevicompactum, P. solitum strain 1, Trichoderma atroviride, Pseudomonas fluorescens, P. fluorescens subgroup G strain 2, P. marginalis, P. putida subgroup B strain 1 and P. syringae strain 1) were shown to significantly reduce development of Pythium root rot of tomato grown in rockwool or in organic medium. Disease reduction was, in most cases, associated with improved plant development. Moreover, T. atroviride and P. putida stimulated reproductive growth of healthy tomato plants in both growing media tested. This effect on growth has been associated, through further studies, to the ability of the microorganisms to produce and degrade indole-3-acetic acid (IAA), which plays an important plant role in plant growth regulation.
Post-harvest application of phosphorous acid materials to reduce potato storage rots. S. B. JOHNSON. Cooperative Extension, University of Maine, Orono, ME 04469.
Late blight incited by Phytophthora infestans and pink rot incited by Phytophthora erythroseptica cause losses in potato storages every year. Tuber-to-tuber spread of the pathogens can contribute to rapid buildup of disease in storages. A study was undertaken during the 2005 storage season to evaluate the effectiveness of Phostrol, Agclor 310, Oxidate, and ProPhyt in reducing the tuber-to-tuber spread of these two pathogens. ‘Shepody’ potato tubers were individually abraded and inoculated with either P. infestans or P. erythroseptica. Treatments were applied 1 hour and 3 hours after inoculation, typical of periods between commercial harvesting and treatment at bin filling. All materials were applied at standard rates in a solution of 64 ounces per ton of potatoes. Tubers were placed into a 55 degree Fahrenheit storage in a randomized complete block design, individually peeled and evaluated for disease after three weeks. Oxidate and Agclor 310 were ineffective in controlling either pathogen. The phosphorous acid materials Phostrol and ProPhyt provided excellent control. Under some conditions, the use of phosphorous materials may be warranted.
Development of scab on peach and nectarine fruit: Effect of fruit age and inoculum concentration. N. LALANCETTE and K. A. McFarland. Rutgers University, AREC, Bridgeton, NJ.
The susceptibility of ‘Redhaven’ peach and ‘Redgold’ nectarine fruit of different ages to scab caused by Fusicladosporium carpophilum was examined during 2006. Fruit on container-grown trees were inoculated with conidia and incubated for 24 h in a growth chamber at 25C and >95% RH. The experimental design was a 2 × 3 × 3 factorial with two cultivars, three inoculation times (22, 36, and 50 d after shuck-split), and three inoculum concentrations (10(^3), 10(^4), and 10(^5) conidia/ml). At each inoculation, fruit length, width, and thickness were recorded. The number of lesions per fruit was assessed during the 35–77 day period following inoculation. Statistical comparison of mean lesion densities across both cultivars and all inoculum concentrations indicated that middle-aged and older fruit were more susceptible than young fruit. In addition, ‘Redgold’ fruit were more susceptible than ‘Redhaven’ fruit and inoculum concentration was directly proportional to disease severity. Results suggest that fruit growth and development may play an important role in the progression of scab epidemics on stone fruit crops.
Characteristics of Meloidogyne spartinae infection of the salt marsh grass Spartina alterniflora. J. A. LAMONDIA and W. H. Elmer. The Connecticut Agricultural Experiment Station, Windsor, CT 06095.
Spartina alterniflora plants from declining saltwater marshes were sampled in 2006 at the Cape Cod National Seashore in Wellfleet, Massachusetts and Hammonassett State Park in Madison, Connecticut. We observed that declining plants and adjacent apparently healthy plants were infected by the root-knot nematode Meloidogyne spartinae. Females, males, juveniles and eggs of M. spartinae were visible inside roots stained with acid fuschin. They were also dissected from swollen terminal galls at the root apex and from pockets present in the root cortex without swelling. The circular to ovoid terminal galls typically stopped root elongation, thereby limiting root growth. Several characteristics of M. spartinae root infection differ from root infection of plants by other common root-knot species. For example, females were oriented with heads toward the root tip in terminal galls, while females in the root cortex were randomly oriented. No egg masses were observed and eggs were free inside the gall or root cortex. The role of M. spartinae in the sudden wetland dieback phenomenon is currently under investigation.
SSCP in Ramorum blight survey diagnostics. R. E. MARRA, S. M. Douglas, and J. Corwin. Department of Plant Pathology & Ecology, Connecticut Agricultural Experiment Station, New Haven, CT 06511.
A single-strand conformation polymorphism (SSCP) procedure, based on the Phytophthora ITS, has been reported to reliably distinguish among Phytophthora species, including P. ramorum. Although this procedure is currently not part of USDA-APHIS-PPQ protocols for detecting P. ramorum, it has potential as a robust complement to the nested PCR and real-time PCR procedures that are part of the official protocols. Among these three procedures, only SSCP unambiguously distinguishes P. ramorum from sister species P. hibernalis and P. lateralis, both of which can produce false positives in nested and real-time PCR. We show here the utility of the SSCP-ITS procedure for identifying P. ramorum in mixed cultures of multiple Phytophthora species. Because mixed Phytophthora cultures are commonly encountered following soil and water sampling protocols for delimitation surveys of P. ramorum-positive nurseries, our SSCP procedure has the potential to streamline the process of identifying P. ramorum in these mixed cultures. This would expedite the time required to release a nursery from mandated quarantine restrictions.
Assessing ambient ozone impact on plant productivity in NY with snap bean genotypes differing in sensitivity. M. T. MCGRATH and J. F. Davey. Dept. Plant Pathology, Cornell University, Riverhead, NY 11901.
Ozone-sensitive (S156) and -tolerant (R331) bean genotypes were field-seeded thrice (May, June, and July) in 2004, 2005, and 2006. They yielded similarly when ozone concentration was low and little injury occurred. But during most of the 9 production periods ozone reached sufficiently high levels that leaves of S156 became severely injured, developed characteristic brown flecking, and then senesced prematurely. Yield was affected. Total weight of pods harvested for fresh-market consumption in 2005 was 17%, 49% and 56% lower for S156 than R331 for plants seeded on 17 May, 17 June, and 13 July, respectively. Total number of bean pods harvested was 14%, 39% and 46% lower. Another set of plants was harvested at pod maturity to assess biological yield. Dry weight of mature pods was 43%, 44%, and 64% lower. Average seed weight was 17%, 24%, and 22% lower. From plant emergence until final harvest for these 3 plantings the exposure index AOT40 (accumulated exposure over the threshold of 40 ppb) during daytime (7 a.m. to 7 p.m.) was 9501, 10451, and 9563 ppb/h, respectively. Crops are negatively impacted when AOT40 values exceed 3000.
Phytophthora ramorum: What is the risk for Eastern Canada? D. RIOUX (1), B. Callan (2), D. McKenney (3), M. Simard (1), S. C. Brière (4), and A. K. Watson (5). (1) NRCan, CFS, Laurentian Forestry Centre, Quebec, QC G1V 4C7; (2) NRCan, CFS, Pacific Forestry Centre, Victoria, BC V8Z 1M5; (3) NRCan, CFS, Great Lakes Forestry Centre, Sault Ste. Marie, ON, Canada P6A 2E5; (4) Canadian Food Inspection Agency, Ottawa, ON K2H 8P9; (5) Dept. Plant Science, McGill University, Ste-Anne-de-Bellevue QC H9X 3V9.
Phytophthora ramorum (Pr) is the causal agent of a disease known as sudden oak death. By request of the Canadian Food Inspection Agency, an updated version of the risk assessment for Pr was produced in May 2006. While the “likelihood of introduction” was estimated to be “high” across Canada, the risk associated with the “consequences of this introduction” was rated “high” for British Columbia and “medium” for Eastern Canada. The global risk would be “high” for British Columbia and “medium” for Eastern Canada. The level of uncertainty of this assessment was rated “medium” and to lower it, research needs were also identified, including determining the potential of Pr to infect different plant species common in Eastern Canada. Preliminary results related to the capacity of Pr to infect and sporulate on seedlings of six tree species are presented.
Relevance to the binary power law of probability distribution choice for estimating the theoretical variance of a random pattern. D. A. SHAH and H. R. Dillard. Dept. of Plant Pathology, NYSAES, Geneva, NY 14456.
Within a cluster sampling framework, the binary power law (BPL) is a convenient, empirical description of the relationship between observed and theoretical variances of the number of infecteds (X) per sampling unit of size n. Fitted parameter values convey information on the extent and variation in aggregation of infecteds at the sampling unit scale. Previous study of the BPL assumed a binomial distribution with constant n for estimating the theoretical variance of X (varX) when infecteds are randomly dispersed. When n is itself variable, the simple Binomial Model may lead to inaccurate estimates of varX. We demonstrate a ‘truncated above’ Poisson-Binomial mixture distribution (taPB) for estimating varX, applied to the number of rust-infected leaves per sweet corn plant (X), where the number of leaves per plant (n) followed some level of Poisson rescaling. varX calculated from the Binomial distribution was lower than that estimated from the taPB distribution in 52 of 60 data sets. BPL goodness of fit, parameter values and their interpretation were all affected by choice of probability model for varX.
Effect of fungicide chemistry and cultivar on the development of cucurbit powdery mildew in pumpkin in New Jersey. A. WYENANDT and N. Maxwell. Rutgers University, ARDC, Bridgeton, NJ.
Strobilurin (azoxystrobin, FRAC group 11) and triazole (myclobutanil, FRAC group 3) fungicides were evaluated for fungicide resistance development in cucurbit powdery mildew in 2005. Five fungicide application programs were applied every 7 to 10 days season-long: i) mancozeb + sulfur alternated with maneb + copper hydroxide (protectant fungicides only), ii) chlorothalonil + myclobutanil alternated with azoxystrobin, iii) myclobutanil + maneb alternated with famoxadone + cymoxanil, iv) chlorothalonil + myclobutanil alternated with myclobutanil, and v) chlorothanolil + azoxystrobin alternated with azoxystrobin. The area under the disease progress curve (AUDPC) for treatments that included weekly applications of azoxystrobin was 1067.0 (‘Howden’) and 1245.0 (‘Magic Lantern’) compared to 625.6 (‘Howden’) and 489.2 (‘Magic Lantern’) for azoxystrobin treatments alternated weekly with myclobutanil. AUDPC values were lowest in both cultivars when treatments included weekly applications of myclobutanil.
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