Rust diseases of cultivated turfgrasses: Understanding an old foe
Rust is a common disease of cool-season turfgrasses that can decrease the aesthetic and economic value of many cultivated species, particularly Kentucky bluegrass (Poa pratensis L.). Chemical control of rust is costly and sometimes ineffective; therefore the use of resistant cultivars is important for the effective management of this disease. Over the past ten years, increased susceptibility to rust has been observed for several Kentucky bluegrass cultivars in the U.S., most notably the once highly resistant ‘Midnight’ types. It has been theorized that new races or even new species of the pathogen may be responsible for this shift in cultivar susceptibility, but the data needed to test this hypothesis is lacking. In the current study, we are using molecular markers to evaluate turfgrass rust populations. To date, 63 rust infested leaf samples have been obtained from graminicolous hosts in North America, the United Kingdom, Australia, and Chile. A reliable DNA extraction protocol was developed and both the complete internal transcribed spacer (ITS) region and 5.8S ribosomal DNA of the samples were amplified and sequenced. Assembled sequences ranged from 682 to 701 base-pairs in length, including the partial sequences of the flanking 18S and 28S rDNA. Bayesian phylogenetic analysis identified Puccinia coronata, P. graminis, and P. striiformis from infested samples, with P. coronata and P. graminis being most prevalent. Sequence data generated from this study has been used to design species-specific molecular markers to develop a real-time PCR protocol that can be utilized by turfgrass breeders, pathologists and diagnosticians for a quick identification of turfgrass rust species.
Compost amendment, a potential alternative to soil fumigation for the control of strawberry verticillium wiltV. BERNIER-ENGLISH (1), T. J. Avis (2), B. Mimee (1), H. Antoun (1), R. J. Tweddell (1)(1) Centre de recherche en horticulture, Pavillon de l’Envirotron, Université Laval, Québec, QC, Canada, G1V 0A6; (2) Department of Chemistry, Carleton University, Ottawa, ON, Canada, K1S 5B6Phytopathology 100:S193
The application of certain composts is known to provide natural biological control against several diseases and appears as an interesting environmentally-respectful approach for the control of plant diseases. Verticillium wilt, caused by Verticillium dahliae, is an important disease affecting strawberry (Fragaria × ananassa). Currently, pre-plant soil fumigation with metham sodium (Vapam®) is commonly used to control the disease. However, Vapam fumigation implies serious risks for health and the environment and often leads to the eradication of beneficial organisms and to a negative shift in the biological equilibrium. The objective of the study was to evaluate the effect of compost application and Vapam fumigation on verticillium wilt incidence and on vegetative development and fruit yield of strawberry plants. Greenhouse and field assays have been conducted with three composts produced from either bovine manure, marine residues or forest bark residues. Composts were applied at different rates to V. dahliae naturally-infected field plots fumigated or non-fumigated with Vapam and planted with strawberries (cv. Seascape). In greenhouse assays, composts were applied to sandy substrate inoculated or non-inoculated with V. dahliae and planted with strawberries (cvs. Seascape and Chambly). The results indicate that incorporation of marine residues compost significantly increased vegetative development of strawberry plants in greenhouse and significantly reduced verticillium wilt incidence in the field. The results also indicate that soil fumigation significantly decreased fruit yield and total soil microbial biomass. Although fumigation significantly decreased soil populations of V. dahliae, it did not reduce verticillium wilt incidence.
Glyphosate effect on DON content and Fusarium graminearum inoculum production in wheat and barleyM. BÉRUBÉ (4), A. Vanasse (4), S. Rioux (1), N. Bourget (1), Y. Dion (2), G. Tremblay (2), G. Bourgeois (3)(1) Centre de recherche sur les grains, Quebec City, Quebec, Canada; (2) Centre de recherche sur les grains, Saint-Mathieu-de-Beloeil, Quebec, Canada; (3) Horticulture Research and Development Centre, Agriculture and Agri-Food Canada, Saint-Jean-sur-Richelieu, Quebec, Canada; (4) Laval University, Quebec City, Quebec, CanadaPhytopathology 100:S193
Fusarium head blight (FHB) is an important disease of wheat and barley, particularly in the wet conditions of Eastern Canada. The principal pathogen associated with FHB, Fusarium graminearum, produces deoxynivalenol (DON), a mycotoxin that makes the grain unfit for food or feed. A recent survey conducted in eastern Saskatchewan revealed that glyphosate application in the previous 18 months within minimum-till system was significantly associated with higher FHB levels in wheat and barley. The objective of this study was to determine the glyphosate effect, used on soybean as the previous crop, on DON content and F. graminearum inoculum production in wheat and barley under three different tillage practices: conventional-till, minimum-till and no-till. Six field experiments (two species × three tillage practices) were conducted in Saint-Augustin-de-Desmaures and Saint-Mathieu-de-Beloeil in 2007 and 2008. Glyphosate and check herbicide treatments chosen according to weed species were applied as main plot treatments on RoundUp Ready™ soybean. The following year, three wheat and three barley cultivars of different FHB resistance levels were seeded as subplot treatments. In each main plot, two Petri plates containing a Fusarium-selective medium were placed facing the ground in order to capture spores coming from the previous crop. In 2007, there were no significant herbicide × cultivar interaction nor herbicide effects on DON content and inoculum production in any of the 12 experiments. In 2008, DON content was significantly (P = 0.046) enhanced by glyphosate use (1.5 vs 1.0 ppm) in only one trial of Saint-Augustin (barley, minimum-till), but there was no significant effect of glyphosate on F. graminearum inoculum production for any of the trials. Therefore, it seems that glyphosate used on soybean the previous year has no or low impact on DON content and F. graminearum inoculum production under Quebec cropping conditions, whatever the tillage practice used.
Fifty years of breeding for disease resistance in turfgrasses: Where we’ve been and where we’re goingS. A. BONOS (1)(1) Rutgers UniversityPhytopathology 100:S193
In the past fifty years, dramatic improvements have been made in breeding for disease resistance in cool-season turfgrasses. Significant breeding progress has been made for leaf spot (caused by Drechslera poae) and stem rust (caused by Puccina graminis) resistance in Kentucky bluegrass (Poa pratensis), gray leaf spot (caused by Pyricularia grisea) resistance in perennial ryegrass (Lolium perenne), brown patch (caused by Rhizoctonia solani) resistance in tall fescue (Festuca arundinacea) and colonial bentgrass (Agrostis capillaris), and dollar spot (caused by Sclerotinia homoeocarpa) resistance in creeping bentgrass (Agrostis stolonifera). There are some diseases for which significant improvements have not been made including red thread (caused by Laetisaria fuciformis) resistance in perennial ryegrass and pythium blight (caused by P. aphanidermatum and other Pythium spp.) in most cool-season turfgrasses. Historically, the dramatic improvements in disease resistance of the cool-season grasses have been attributed to traditional/conventional breeding techniques; however, it is likely that functional genomics and molecular techniques that identify specific genes and mechanisms involved in disease resistance will be significant in the development of cultivated turfgrasses in the future.
Evaluation of a dynamic model for primary infections caused by Plasmopara viticola on grapevine in QuebecT. CAFFI (2), V. Rossi (2), O. Carisse (1)(1) Agriculture and Agri-Food Canada, Horticultural Research Centre, 430 Gouin boul., Saint-Jean-sur-Richelieu, Québec, Canada, J3B 3E6; (2) Istituto di Entomologia e Patologia vegetale, Università Cattolica del Sacro Cuore, Via E. Parmense 84, I-29100 Piacenza, ItalyPhytopathology 100:S194
A dynamic model for the prediction of Plasmopara viticola primary infections was evaluated by comparing model predictions with disease onset in 43 cases (locations per years) in Eastern Canada in 2008 and 2009. The model simulates the development of all oospore cohorts during the primary inoculum season, including: oospore germination; production and survival of sporangia; release, survival and dispersal of zoospores; infection and incubation. Bayesian analysis was used to evaluate the sensitivity, specificity and accuracy of the model predictions. First seasonal onset of downy mildew symptoms ranged between 8 June and 29 June depending year and vineyard. For each vineyard, one to 20 simulation runs were performed depending on the number of oospore cohorts formed, for a total of 545 simulations. All observed infections were correctly predicted by the model. A total of 313 simulations resulted in no infection and in 284 cases no disease developed. Only one observed infection was not predicted by the model. Finally, 29 out of 313 simulations predicted an infection that did not result in observed disease. From this validation analysis, it was concluded that this model could be used in Eastern Canada to predict the occurrence of the first infection and trigger the initiation of a fungicide spray program against grape downy mildew.
Age-related susceptibility of strawberry leaves and berries to infection by Podosphaera aphanisO. CARISSE (1), J. Bouchard (2)(1) Agriculture and Agri-Food Canada, 430 Gouin, St-Jean-sur-Richelieu, Qc, Canada, J3B 3E6; (2) Plant Science department, Laval University, Quebec City, Quebec, Canada, G1K 7P4Phytopathology 100:S194
Powdery mildew, caused by Podosphaera aphanis, is a major disease of strawberry for which only few management tools are available. The importance of the disease varies with production systems (June bearing vs day neutral) which could be explained in part by the concurrent presence of susceptible leaves or berries and abundant airborne inoculum. Age-related susceptibility was studied by inoculating strawberry leaves and berries at different age group. The experiment was conducted for the June bearing cultivar ‘Jewel’ and the day neutral cultivar ‘seascape’. On eight occasions in 2007, five plants for each cultivar were inoculated with dry conidia using a settling tower. They was a significant effect of leaf and berry age group on the susceptibility which decreased exponentially as leaves or berries aged to reach zero when the leaves were completely expanded or the berries at the pink stage at the time of inoculation. The proportion of maximum mildew severity as a function of leaf or berry growth stage was predicted using non-parametric regression (R2 = 0.96 to 0.97). The prediction values were further validated with data collected in field naturally infected by P. aphanis. There was a linear relation between predicted and observed proportion of maximum mildew severity (R2 = 0.95 to 0.98). The results of this study showed that timing fungicide sprays based on periods of high leaf and berry susceptibility should greatly improve management of strawberry powdery mildew.
First report of clubroot caused by Plasmodiophora brassicae on spring canola in MaineS. B. JOHNSON (1), D. H. Lambert (1), P. J. Sexton (1)(1) University of Maine, Orono, ME, USAPhytopathology 100:S194
Spring canola (Brassica napus L.) was introduced into Maine as a potential oilseed crop in 1999. Since then, acreage has increased from 120 to about 3500 acres and is rapidly becoming an important rotation crop with potato. In August of 2008, canola plants in two fields in Aroostook County were observed with classical symptoms of clubroot. Severely affected plants were stunted and ripening prematurely. Many of the plants had the roots fully involved with the disease. Infected plants were collected from the fields. The roots were macerated and the resultant slurry allowed to settle. Abundant spores of Plasmodiophora brassicae were observed in the slurry. Spring canola was sown and inoculated with an excess of 50,000 spores per plant. A like number of spring canola plants were not inoculated. All canola plants were examined twelve weeks after inoculation. Typical root clubbing symptoms were evident in all of the inoculated plants. The roots were macerated and Plasmodiophora brassicae spores were observed from the resultant slurry. No symptoms or spores were present in any of the uninoculated plants. The pathogen is not a recent introduction to Maine. Pathogen buildup or spread to uninfested areas is a concern in Maine. Broccoli is susceptible to Plasmodiophora brassicae and is an important cash crop often used in rotation with potatoes in Maine. The economic impact to the broccoli industry has the potential to be greater than the impact to the canola industry. To our knowledge, this is the first report Plasmodiophora brassicae on spring canola in Maine.
White rot of garlic caused by Sclerotium cepivorum -- a new disease in MaineS. B. JOHNSON (1), D. H. Lambert (1), B. Watt (1), R. Kersbergen (1)(1) University of Maine, Orono, ME, USAPhytopathology 100:S194
There are over 70 commercial garlic (Allium sativum var ophioscorodon) growers in Maine representing all 16 counties. Most garlic producers in Maine are market gardeners producing many crops. However, the contribution to farm income from garlic is disproportionably large when compared to the area planted. Garlic grown in Maine is distributed within Maine and to other states. In July of 2008, garlic plants were observed with symptoms which appeared to consistent with white rot. Severely affected plants were stunted with yellowing and wilting of the leaves. Bulb decay was present as were sclerotia. Infected plants were collected from the field. Sclerotium cepivorum Berk was isolated from the diseased bulbs. Established chives (Allium schoenoprasum) were used as susceptible host. These were inoculated with a sclerotia/mycelial mixture. Uninoculated chives plants were used as controls. All chives plants were examined twenty weeks after inoculation. Typical symptoms were evident in all of the inoculated plants. The pathogen, Sclerotium cepivorum, was isolated from the inoculated and symptomatic plants. No symptoms were present in any of the uninoculated plants. The pathogen is a recent introduction to Maine. While reputedly present a year or two previously, disease has now been confirmed. Pathogen buildup and spread to uninfested areas is a concern in Maine. The current practice of importation of seed stock and exchange of live plant material may contribute to new appearances and further spread of the disease. At present, there is no current knowledge on the distribution and prevalence of garlic white rot.
Solutions to the imbroglio over the nomenclature of Gremmeniella abietinaG. LAFLAMME (1)(1) Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre, Quebec, QC, Canada G1V 4C7Phytopathology 100:S194
Scleroderris canker is caused by the fungus Gremmeniella abietina. In North America, the disease was first noticed in red pine plantations in Michigan, USA, in 1951 and was then referred to as the X disease. In 1954, similar damage was reported in Ontario, Canada. The causal agent was first identified in Maple, Ontario, in 1962, as Scleroderris lagerbergii. Taxonomists changed the name of the genus, in 1969, to Ascocalyx and Gremmeniella. Two years later, a third genus name appeared in the literature: Lagerbergia. Within the accepted species Gremmeniella abietina, three races were created in 1975: North American, European and Asian. In 1989, two varieties were recognized, one representing the three previous races and the second for G. abietina found on spruce and fir. In the 1990s, based on the host affected by the disease, a new vocabulary appeared: small tree type and large tree type, or, according to pathogen traits, types A and B. This was followed later by amplitypes (European, Northern, Alpine) which evolved later into biotypes (Alpine, Fennoscandian and European). A new biotype from Spain will soon be added to this list. Race and type are not valid ranks in fungal taxonomy. After molecular analyses, it now seems more evident that G. abietina is a European species, known in North America under the name European race. Fungi found on pine, fir and spruce in North America and on Todo-fir in Japan (the latter is currently referred to as the Asian race) are four different species. The case of G. laricina being one or two species in Europe and North America remains to be clarified.
Integration of biofungicides and conventional fungicides for management of peach brown rotN. LALANCETTE (1), K. McFarland (1)(1) Rutgers University, Agricultural Research & Extension Center, Bridgeton, NJ, USAPhytopathology 100:S195
The biorational fungicides Serenade MAX (Bacillus subtilis QST 713), Kaligreen (potassium bicarbonate), and Trilogy (hydrophobic extract of neem oil) were examined in integrated programs with conventional fungicides during the 2009 growing season for management of brown rot blossom blight and fruit rot on ‘Encore’ peach. Experimental programs consisted of low and high rates of each biofungicide applied during bloom (pink, full bloom, and petal fall timings) for blossom blight control and as the middle of three applications at 18-, 9-, and 1-day preharvest for rot control during the fruit ripening period. Treatments were applied using an airblast sprayer (935 L/ha) to single trees arranged in a randomized complete block design with four blocks; non-treated buffer trees surrounded each treatment tree. A standard commercial program and non-treated control (NTC) were included for comparison. Results of analyses of variance of both the blossom blight and fruit rot dependent variables showed significant model and treatment effects. Blossom blight canker incidences (% shoots with canker) for Trilogy-low (2.5%), Serenade-low (1.3%), Kaligreen-high (1.3%), and Trilogy-high (0%) were significantly less than the NTC (10.0%) and not significantly different from standard (0%). These integrated treatments provided 75–100% control of blossom blight canker development. At harvest, all six integrated programs had significantly less brown rotted fruit (22.0–35.3% fruit rot) than the NTC (90.4%) and statistically equivalent incidence of rot to the standard (16.2%). Similar results were obtained for a postharvest evaluation of fruit after 3-days incubation; integrated programs had 14.7 to 29.3% fruit with brown rot versus 26.3% for the standard. These results demonstrated that biorational fungicides can be integrated with conventional fungicides to provide effective brown rot control programs. Furthermore, the results suggest that early season blossom blight control may be possible with biofungicides alone. Data from additional seasons are required to substantiate these findings.
Evaluation of strawberry breeding lines for tolerance to black root rot and black vine weevil feedingJ. A. LAMONDIA (1), R. S. Cowles (1)(1) Connecticut Agricultural Experiment Station, Windsor, CT, USAPhytopathology 100:S195
Perennial strawberries are an important high value crop in the northeast U.S. Root diseases and root-feeding insects reduce yield and strawberry planting longevity. The most important root disease is strawberry black root rot, caused by Rhizoctonia fragariae. Feeding by root weevil larvae, especially black vine weevil (BVW), also reduces root mass and damages or kills plants. We conducted field assessment of strawberry cultivars over three years for yield, vigor, and root health to identify tolerance to black root rot as well as leaf feeding preference bioassays to identify tolerance to BVW. Several cultivars were identified as having characteristics desirable as parents for crosses. Primetime and Lester exhibited resistance or tolerance to black root rot and non-preference to BVW in feeding preference trials; the cultivar Idea was moderately susceptible to root rot, but produced a large, vigorous root system. Progeny of crosses made between Primetime, Lester, Allstar, Delmarvel, and Idea were carefully selected for resistance or tolerance to black root rot in greenhouse pots and in the field in infested soils as well as low preference in BVW feeding trials. Progeny were also screened for fruit yield, size, and flavor. Selection over three years reduced the progeny population from >4,000 genotypes to a few elite clones with promising horticultural characteristics, tolerance to black root rot, and low feeding preference by BVW. Our results demonstrated that sufficient variation exists in certain octoploid parents to develop effective resistant/tolerant lines. Because there were differences in disease reactions between greenhouse evaluations of juvenile plants and field evaluations on mature plants, evaluations in the field are essential in selecting for black root rot tolerance.
Changing climate, changing forests: Two decades of tree dieback and decline in MaineW. H. LIVINGSTON (1)(1) University of Maine, Orono, ME, USAPhytopathology 100:S195
A number of tree dieback and decline episodes have occurred in Maine forests over the past 25 years: Ash dieback 1985–95 (Fraxinus nigra), island spruce decline 1995–2000 (Picea glauca), white pine decline 1995–2001 (Pinus strobes), beech decline 1999–2004 (Fagus grandifolia), and balsam fir decline 1999–2004 (Abies balsamea). In all studies, dendrochronology was the key analytical approach for establishing consistencies between likely inciting stresses and diebacks or declines. Historical abandonment of agricultural fields created conditions where native tree species regenerated on sites where they were not well adapted for long-term survival. In white pine decline, trees regenerated in high densities on sites where white pine rooting patterns would not penetrate deeply into the soil. A drought in 1995 incited a decline in these stands. On Maine coastal islands, abandonment of sheep pastures around 1900 allowed white spruce to regenerate in pure stands not historically found on the islands. As the stands matured, eastern dwarf mistletoe (Arceuthobium pusillum) and spruce beetle (Dendroctonus rufipennis) built-up populations and killed stands. Droughts are common inciting events in other diebacks and declines (ash, beech, balsam fir) in Maine where typical years do not have a dry season. Finally, warmer winter temperatures are allowing buildup of insect populations of beech scale (Cryptococcus fagisuga) and balsam woolly adelgid (Adelges piceae) that predispose trees to declines incited by drought. The combination of land use histories altering normal disturbance and successional patters, years of drought, warmer winters, and build-up of invasive pests have been adversely affecting survival of trees in Maine.
Sensitivity of Phytophthora capsici isolates from cucurbits in the northeastern U.S. to dimethomorph, cymoxanil, and mefenoxamA. M. MADEIRAS (1), R. L. Wick (1), D. R. Cooley (1)(1) University of Massachusetts, Amherst, MA, USAPhytopathology 100:S195
Phytophthora capsici has become an important pathogen of cucurbit crops in the northeastern United States over the last few years. Monitoring fungicide resistance development in this pathogen is crucial to the success of disease control programs. The purpose of this study was to determine sensitivities of local P. capsici isolates to dimethomorph, cymoxanil, and mefenoxam. Single spore isolates from each of ten cucurbit fields in New York and Massachusetts were randomly selected and assayed. The 37 isolates tested for sensitivity to dimethomorph demonstrated a range of 50% effective concentration (EC50) values from 0.21 to 0.63 mg/L. Of 37 isolates tested for sensitivity to cymoxanil, 21 (56.8%) had EC50 values >50 mg/L and 16 (43.2%) had EC50 values <50 mg/L. EC50 values for cymoxanil ranged from 1.04 to 132.8 mg/L. Of 39 isolates tested, 35 (89.7%) were sensitive (relative colony diameter [RCD] <30% of nonamended control) and 4 (10.3%) were intermediately sensitive (RCD 30–90%) to mefenoxam. The results of this study parallel those of investigators in other locations and provide information which can be used to monitor changes in dimethomorph, cymoxanil, and mefenoxam sensitivity in populations of P. capsici on cucurbits in the northeastern U.S.
Elucidation and management of bacterial diseases on sweet onion in PennsylvaniaM. A. Mansfield (1), B. K. GUGINO (1)(1) The Pennsylvania State University, University Park, PA, USAPhytopathology 100:S195
Sweet onions are an emerging crop in Pennsylvania; however, they are susceptible to a number of bacterial diseases that cause leaf and bulb decay. In 2008, it was estimated that 50% of the sweet onion crop in Lancaster County was culled in the packing shed as a result of bacterial diseases. In addition, recent studies reported an association between disease incidence and severity on onions grown using plastic mulches typical of production in PA. Our objectives were to identify and characterize the bacteria associated with symptomatic onions in commercial fields and evaluate the effect of bare soil, straw and different types/colors of plastic mulches with and without thrips control on bacterial disease incidence and severity in a replicated field trial. Based on preliminary morphological identification and pathogenicity tests using an onion slice bioassay, Burkholderia cepacia, B. gladioli, Erwinia caratovora, E. chrysanthemi, Pantoea ananatis, P. agglomerans, Pseudomonas syringae, P. viridiflora, Xanthomonas axonopodis, and X. campestris were identified from symptomatic onions collected from 15 commercial fields across PA in 2009. This is the first report of P. ananatis and P. agglomerans causing disease on onion in PA. Further molecular characterization of these isolates is ongoing. In the field trial, bacterial diseases were most prevalent on onions grown on bare soil followed by those on white plastic mulch without thrips control. Additional data will be presented on the effects of mulch type and thrips control on onion bacterial disease incidence and severity and its implication for disease management.
Proposing a new species of Fusarium: F. ‘aestuarinus,’ a pathogen of Spartina alterniflora associated with wetland dieback in eastern marshesR. E. MARRA (1), W. H. Elmer (1)(1) Connecticut Agricultural Experiment Station, New Haven, CT, USAPhytopathology 100:S195
Sudden Vegetation Dieback (SVD) is a syndrome characterized by rapid loss of vegetation, particularly smooth cordgrass (Spartina alterniflora). The phenomenon has been observed in salt marshes of the eastern seaboard extending from Louisiana north to Maine. Morphological assessments of fungi associated with S. alterniflora in SVD sites have revealed a preponderance of isolates in the genus Fusarium that could not be assigned to known species. Based on morphology and greenhouse pathogenicity studies, the isolates separated into two groups, pathogens and nonpathogens. Phylogenetic analyses of three nuclear genes – beta-tubulin, calmodulin, and translation elongation factor 1-alpha – corroborated morphological and pathogenicity studies. Phylogenies were constructed using 20 pathogenic isolates, 18 nonpathogenic isolates, and nine previously described Fusarium species. Maximum Parsimony and Maximum Likelihood analyses, using individual-gene and combined-gene datasets, produced concordant topologies that strongly support the hypothesis that the pathogenic and nonpathogenic isolates constitute two phylogenetically distinct clades. From these data, we conclude that the pathogens represent a single species in the Fusarium section Sporotrichiella, for which we propose the name Fusarium ‘aestuarinus.’ Isolates in the nonpathogenic group further cluster into two distinct clades, both clearly belonging to the F. incarnatum-equiseti species complex. Additional analyses reveal that beta-tubulin sequences from F. langsethiae and F. equiseti share strongest similarities to that from a more distantly related ascomycete, Arthrinium sp., highly suggestive of horizontal gene transfer, and warranting further study.
Occurrence of basil downy mildew in the eastern U.S. in 2009M. T. MCGRATH (3), C. A. Wyenandt (2), R. N. Raid (5), M. Babadoost (1), R. L. Wick (4)(1) Department of Crop Sciences, University of Illinois, Urbana, IL, USA; (2) Department of Plant Biology and Plant Pathology, Rutgers University, Bridgeton, NJ, USA; (3) Department of Plant Pathology and Plant-Microbe Biology, Cornell University, LIHREC, Riverhead, NY, USA; (4) Department of Plant Soil and Insect Sciences, University of Massachusetts, Amherst, MA, USA; (5) University of Florida, Everglades Research & Educ Ctr, Belle Glade, FL, USAPhytopathology 100:S196
Downy mildew (caused by Peronospora belbahrii) is a new disease of basil in the USA. It was first detected in FL in Oct 2007. There were several reports in the eastern USA in 2008. Occurrence in 2009 was monitored through sentinel plots planted with the cucurbit downy mildew project plots throughout the eastern USA and a publicly-accessible spreadsheet on the web. Downy mildew was reported in 2009 on basil grown in greenhouses and outdoors, in both commercial crops and gardens. The first reported observation was 14 Jan in GA. Downy mildew was also reported in FL, SC, NC, TN, VA, DE, NJ, PA, NY, CT, MA, VT, IL, IN, ND, and CA. Not all reports were made by plant pathologists or confirmed by microscopic examination. Entries in the spreadsheet include the reporter’s name and method of diagnosis. Downy mildew was reported widespread with large impact in some areas. In NJ, symptoms were first observed in June and progressed during the season throughout the production area which covers more than 600 A. Downy mildew was also widespread in FL, and in IL where commercial basil field production is estimated at 550 A. Entire crops have been lost because of this disease. Downy mildew is now recognized to be established in the USA and is anticipated to continue occurring every year. Until host plant resistance becomes available, it appears that downy mildew may force growers to make drastic changes in production practices, principally applying fungicides to a crop that rarely needed pesticide applications previously.
Control of foliar diseases in organically-produced tomato with biopesticidesM. T. MCGRATH (1), G. M. Fox (1)(1) Department of Plant Pathology and Plant-Microbe Biology, Cornell University, LIHREC, Riverhead, NY, USAPhytopathology 100:S196
Tomato is an important crop for organic vegetable growers. Foliar diseases occur commonly in the northeastern U.S. and can reduce fruit quality and quantity. EPA-defined biopesticides compliant with U.S. National Organic Program were evaluated in 2008 and 2009 for naturally-occurring diseases in trellised fresh-market tomato. Main diseases were powdery mildew and Septoria leaf spot. Applications were made weekly with a back-pack sprayer and hand-held boom beginning before symptoms were seen. In 2008, degree of control calculated from canopy severity on 6 Oct was 75% for powdery mildew and 58% for Septoria leaf spot with Actinovate SP (0.0371% Streptomyces lydicus). It was 98% and 68% with Companion (0.03% Bacillus subtilis GB03), 100% and 61% with Regalia (5% extract of Reynoutria sachalinensis), 99% and 54% with Organocide (5% sesame oil), and 86% and 0% for Sporatec AG (18% rosemary oil, 10% clove oil, and 10% thyme oil). Degree of control of both diseases obtained with Regalia alternated with Kocide 3000 (46% copper hydroxide), Organocide plus Kocide (both at low rates), and Sporatec plus Saf-T-Side was not significantly different from Kocide alone applied weekly or the conventional fungicide program (control of 99–100% and 94–100%). Copper fungicide is considered a standard being the main product used currently by organic growers. Another biopesticide, Taegro (24.5% Bacillus subtilis var. amyloliquefaciens strain FZB24), was only effective for powdery mildew (56%). In 2009, Septoria leaf spot was the dominant disease. The most effective biopesticides were Companion and Actinovate. They were at least as effective as Kocide. Similar control was obtained with low rates of Organocide plus Kocide. The most effective treatments in 2009 included conventional fungicides used alone or combined with biopesticides.
Identification and characterization of silicon transporters in wheat (Triticum aestivum)J. MONTPETIT (1), J. Vivancos (1), W. Rémus-Borel (1), C. Grégoire (1), F. Belzile (1), R. R. Bélanger (1)(1) Université Laval, Quebec, Quebec, CanadaPhytopathology 100:S196
Silicon (Si) is not considered as an essential element for plant growth but its supply is known to be beneficial, namely in preventing biotic and abiotic stresses. However, its positive effects are variable since in planta accumulation differs among plant species and a direct correlation between benefits and absorption has been shown. Some species of the Gramineae family can accumulate up to 10% on a dry weight basis while others only accumulate less than 0.1%. Recently, studies with rice have shown that Si transport is mainly regulated by two genes, Lsi1 and Lsi2. Lsi1-2 like genes have also been reported in barley and corn. The objective of this project was to identify and characterize orthologous Si-transport genes in wheat, given the ability of this plant to accumulate high Si concentrations. With the design of degenerate primers, two genes presenting high homology (>80%) to Lsi1 and Lsi2 in rice were identified. Following their isolation, the Si-transport activity of Lsi1 was verified in Xenopus laevis oocytes, a heterologous system. Functional characterization is in progress in the model plant Nicotiana tabacum by the intra-cellular localization of these transporters. Preliminary results suggest that Lsi1 transporter in wheat is localized across the entire plasma membrane, unlike OsLsi1 located in specific distal parts of the cell. This localization of Si transporters could explain the difference in Si absorption between wheat and rice.
Breeding hybrid poplar in Québec to improve their resistance to Septoria musiva M.-J. MOTTET (1), P. Périnet (1)(1) Ministère des Ressources naturelles et de la Faune, Direction de la recherche forestière, 2700, rue Einstein, Québec, Qué., Canada G1P 3W8Phytopathology 100:S196
The poplar (Populus spp.) breeding program in Québec is based on multi-trait selection including disease resistance. Infection by the native fungus Septoria musiva Peck causes severe stem deformation and breakage leading to top dieback or death of the trees. In Québec, bioclimatic conditions have a significant impact on canker incidence and severity; damage generally decreases following a south-north gradient. For about 20 years the breeders have been selecting clones to improve Septoria canker resistance. Interspecific hybridization aims to capture growth vigour, cold hardiness, and site adaptability from the species P. trichocarpa (T) and P. maximowiczii (M) while retaining Septoria resistance from P. deltoides (D), and to some extent P. nigra (N) and P. balsamifera (B). Despite the high susceptibility of T and M species and considering that Septoria resistance is apparently recessive, improvement in resistance was accomplished in some species and hybrids (T, N, TD, DN x M, NM, MB) through selection and testing. The objective is to incorporate resistance or tolerance genes originating from many sources in order to achieve durable resistance. Progenies or clonal populations are first screened in nursery or early tests where artificial inoculations with different isolates contribute to accelerate the screening. Then, superior clones are tested in several locations including Septoria prevalent sites. More than 5000 clones have been evaluated since 1969. For now, about 40 clones belonging to different hybrid types and families are used for planting in Québec including 18 resistant/tolerant clones in Septoria zones. Some of those clones are periodically replaced to improve traits of interest and increase genetic diversity. Even if Septoria canker expands in geographic range since year 2000, selection for Septoria resistance has not been defeated by evolution of new races or other pest.
The potential for post-harvest foliar urea sprays to reduce ascospore production by Venturia inaequalisR. NORTON (1), C. A. Smith (1), W. E. MacHardy (1), W. Lord (1)(1) University of New Hampshire, Durham, NH, USAPhytopathology 100:S196
Apple scab, a disease caused by the ascomycete Venturia inaequalis, is an important disease of apples in the Northeast. In the Northeast, apple scab is typically controlled by frequent applications of chemical fungicides in the spring. Consumer concerns about the potential harmful effects of pesticides on human health and the environment has created a need for alternative management options. We are examining the use of urea, as an alternative to chemical fungicides for controlling apple scab. Although previous studies have shown that urea reduces the production of ascospores, the primary inoculum for apple scab, the studies did not compare application rate, timing of application, and winter hardiness in a single comprehensive study. Cortland leaves, infected with V. inaequalis, were treated immediately post-harvest, at the start of leaf fall, and at 95% leaf fall. A 5% urea application was made either as a single spray or in split applications. Our data suggests that post-harvest foliar urea applications significantly reduce the production of ascospores in V. inaequalis. In conjunction with the ascospore study, we are also examining the effects of post-harvest foliar urea sprays on winter hardiness, fruit set, and foliar nitrogen content. Results indicate that post-harvest foliar urea applications have no adverse effects on tree health.
The effect of demethylation inhibitor fungicides on Sclerotinia homoeocarpa population structuresJ. T. POPKO (2), C. Ok (2), W. R. Autio (2), M. T. McGrath (1), G. Jung (2)(1) Department of Plant Pathology and Plant-Microbe Biology, Cornell University; (2) Department of Plant, Soil and Insect Sciences, University of Massachusetts-AmherstPhytopathology 100:S197
Dollar spot (Sclerotinia homoeocarpa F.T. Bennett) is the most economically important turfgrass disease in North America. Dollar spot is primarily controlled by fungicide application on golf courses; however, fungicide resistance has been confirmed in three of the five fungicide classes used to control dollar spot. Among the confirmed classes, the sterol demethylation inhibitor (DMI) fungicide class is the most widely used. The objective of this project was to investigate the effect of propiconazole (DMI) rates on changes in dollar spot population structure using in-vitro fungicide assays and field efficacy results. Two sites (Hickory Ridge Country Club, HRCC and South Deerfield Turf Research Center, SDTRC) were selected for the experiment. Dollar spot was sampled prior to fungicide application and at the end of the experiment to examine change in population structure. Samples were also taken 7 and 14 days after fungicide application from infection centers that displayed actively growing mycelia to determine the sensitivity of isolates causing reduced DMI efficacy. All samples were subjected to an in vitro fungicide assay using a single discriminatory concentration (0.1 µg a.i./ml) of propiconazole to determine relative mycelia growth percentage (RMG%). Propiconazole (0.44, 0.88, 1.28 and 1.72 kg a.i. ha–1) and the industry standard chlorothalonil (non-DMI/12.67 kg a.i. ha–1) fungicides were applied to both sites to test field efficacy. The initial sampling from the HRCC (n = 433 isolates) revealed the pre-existence of DMI sensitive and insensitive sub-populations. All isolates from SDRC (n = 458) were DMI sensitive. All samples from propiconazole treated plots 7 and 14 days after application contained only isolates from the insensitive sub-population regardless of rate applied at HRCC. Non-DMI treated plots (untreated or chlorothalonil) sampled 7 and 14 days after application contained isolates of both sub-populations. Reduced field efficacy using propiconazole was observed at HRCC, whereas complete control was observed at the SDRC.
Structural defense mechanisms in trees: What’s new?D. RIOUX (1)(1) Natural Resources CanadaPhytopathology 100:S197
As is the case for many herbaceous plants, preexisting defense structures are essential in helping trees resist pathogens or mechanical damage. For instance, by insulating the inner living tissues from heat damage, the thick bark of sequoia trees is considered an important factor in their tolerance to fire. Another example is the wax that covers the foliage that often has an influence on the germinating rate of some pathogen spores or can even help prevent the penetration of stomata. When such preformed defense elements fail to impede pathogen ingress, trees respond by forming different structures to limit or stop pathogen invasion. Compartmentalization processes are certainly among the most important induced mechanisms that explain tree resistance to various stresses. Basically, it involves the formation of barriers that bound infected tissues and thus limit the extent of such lesions in trees. Lignin and suberin often impregnate the walls of cells involved in compartmentalization whereas phenols are usually a major component of their cytoplasm. Lately, resistance of eucalyptus trees to a leaf pathogen has been attributed to these types of compartmentalization responses. Likewise, in a recent study, it was clearly shown that such reactions occur in elm calli inoculated with a wilt pathogen. Genes and substances potentially involved in metabolic pathways leading to compartmentalization barriers have been reported in recent years. In particular, methyl jasmonate can induce the formation of traumatic resin canals in conifers, and these canals are regularly found in compartmentalization xylem barriers. Interestingly, embolism seems to be a significant trigger of compartmentalization and this could result in practical applications, e.g. when sugar maple trees are tapped to collect their sweet sap. Finally, even though compartmentalization structures are composed of antifungal compounds, some fungi have developed strategies to breach these defensive tissues.
Summer N-fertilization effects on annual bluegrass putting green turfJ. A. ROBERTS (1), J. A. Murphy (1), B. B. Clarke (1)(1) Rutgers University, New Brunswick, NJ, USAPhytopathology 100:S197
Anthracnose, caused by Colletotrichum cereale Manns, is a devastating disease of putting green turf. Increased N fertility has been reported to reduce anthracnose severity on annual bluegrass [Poa annua L. f. reptans (Hausskn) T. Koyama] turf. In 2007, a 3-yr field study was initiated in North Brunswick, NJ to determine the effect of rate and frequency of soluble-N fertility during mid-season on anthracnose severity of annual bluegrass turf maintained at 3.2 mm. The date of initiating N fertilization (mid-May vs. mid-June) was also evaluated during 2008 and 2009. Nitrogen was applied at 4.9 kg ha–1 every 1, 2, 4 and 8 wk and 9.8 kg ha–1 every 2 and 4 wk as a solution of NH4NO3. Anthracnose severity, assessed as area under the disease progress curve, was reduced linearly with increasing total N rate (9.8 to 58.8 kg ha–1). Nitrogen applied at 58.8 kg ha–1 total (4.9 kg ha–1 wk–1 or 9.8 kg ha–1 2 wk–1) had the greatest reduction in anthracnose severity throughout the study. Nitrogen applied at 29.9 kg ha–1 over the season (4.9 kg ha–1 2 wk–1) was the lowest N rate to significantly reduce disease severity, and anthracnose was most severe on turf receiving N at 19.6 and 9.8 kg ha–1 (4.9 kg ha–1 4 wk–1 or 8 wk–1) over the season. Initiating N fertilization before symptom expression (mid-May) reduced anthracnose severity compared to fertilization initiated at the onset of disease (mid-June) in 2008. Thus, fertilization techniques that increased mid-season N fertility, within the range of 29.9 to 58.8 kg ha–1, were effective at reducing anthracnose severity on annual bluegrass turf.
Using lime-sulfur to control sooty blotch and flyspeck in organic apple production in southeastern New York StateD. A. ROSENBERGER (1), F. W. Meyer (1), A. L. Rugh (1)(1) Cornell University’s Hudson Valley Lab, Highland, NY, USAPhytopathology 100:S197
Lime-sulfur (LS) was applied to control sooty blotch and flyspeck (SBFS) on apple fruit in five trials in which replicated plots were sprayed to drip using a handgun. In 2005, Golden Delicious apples receiving two sprays of LS at 10 ml/L during July followed by one spray of thiophanate-methyl plus captan (210 and 600 mg/L of active ingredient) in Aug had no more SBFS than trees that received thiophanate-methyl plus captan (TM-C) in all three sprays. In 2006, four summer applications of LS at either 5 or 10 ml/L on a 20-day interval or six sprays at 2.5 ml/L on a 10-day interval controlled flyspeck just as well as four sprays of TM-C, but a four-spray program of LS at 2.5 ml/L was less effective. In 2007, LS at 2.5 ml/L was applied alone on 7 and 30 June and in a tank mix with 300 mg/L of Cuprofix Disperss (71% basic copper sulfate) on 24 July and 14 Aug. This treatment reduced flyspeck by only 77–78% on Empire and Golden Delicious fruit compared to unsprayed controls whereas TM-C provided 94–96% control. During the very wet summer of 2009, 98% of unsprayed Royal Court fruit failed to meet the U.S. Fancy grade at harvest due to SBFS whereas eight summer sprays of LS at 2.5 ml/L resulted in 65% out-of-grade fruit. When the eight-spray LS program was modified by applying LS alone in June and Sep but adding 318 mg/L of Nordox (56% copper oxide) to LS in the four July-Aug sprays, only 32% of fruit were down-graded for SBFS but 26% showed copper injury. LS can be used to control SBFS in organic apple production, but additional research is needed to optimize rates and spray timings and to determine if LS applied during summer reduces fruit size.
Stem susceptibility of six eastern Canadian tree species to Phytophthora ramorumM. SIMARD (2), S. C. Brière (1), A. K. Watson (3), D. Rioux (2)(1) Canadian Food Inspection Agency; (2) Canadian Forest Service; (3) McGill UniversityPhytopathology 100:S197
Phytophthora ramorum (Pr) is an emerging pathogen that causes diseases known as sudden oak death, ramorum leaf blight and ramorum shoot dieback. Even though Pr has been reported to naturally infect around 120 species, it has not been detected in the wild in eastern North America. However, there is real concern that Pr could be introduced and spread into this area. To better estimate this risk, seedlings of the following six eastern Canadian forest species were stem-inoculated with Pr: Abies balsamea (Ab), Acer saccharum (As), Betula alleghaniensis (Ba), Fraxinus americana (Fa), Larix laricina (Ll), and Quercus rubra (Qr). Bark necrosis, colonization by Pr as well as host defense reactions were evaluated. Two months after inoculation, nearly 25% of Ll and Ab seedlings died. Necrotic areas on the bark were larger in Ll, Ab, and Qr than in Fa, As, and Ba. Chlamydospores were observed close to the inoculation point in the phloem of Ll, Ab, and Qr. Pr hyphae were abundant in the phloem and cambium but also in the xylem of the two coniferous species where the colonization is facilitated mainly through the invasion of ray cells. In broadleaf species, hyphae were observed in a few xylem vessels and fibers close to the inoculation point, except for Qr where Pr was abundant in xylem vessels and still present up to 5 cm above the inoculation wound. However, among the six species, Qr was the only one where defense reactions were clearly apparent, especially when the inoculation occurred later in the growing season. Overall, Ab, Ll, and to a certain extent Qr appeared susceptible to Pr and they could be killed should Pr be introduced during conditions conducive to disease development.
Molecular characterization of the biocontrol activity of Pseudozyma flocculosaB. TEICHMANN (1), F. Lefebvre (1), C. Labbé (1), R. Bélanger (1)(1) Biocontrol Laboratory, Pavillon de l’Envirotron, Université Laval, 2480, boul Hochelaga, Québec, G1V 0A6, CanadaPhytopathology 100:S198
The basidiomycetous fungus P. flocculosa is a natural inhabitant of the phyllosphere and has been isolated as a biocontrol agent (BCA) against powdery mildews. It secretes large amounts of an antifungal cellobiose lipid, flocculosin, presumably involved in its biocontrol activity. However, the molecular and genetic basis of glycolipid production and secretion is largely unknown in P. flocculosa. The related fungus Ustilago maydis secretes a highly similar glycolipid, ustilagic acid (UA), which also displays antibacterial and antifungal activity. Recently, a biosynthetic gene cluster was characterized in U. maydis and found to contain all genes required for the efficient production and secretion of UA. By analyzing the database of the recently sequenced genome of P. flocculosa, we hypothesized that a homologous gene cluster regulating flocculosin synthesis could be found in P. flocculosa. Comparison of the sequences of all 12 genes against the genome of P. flocculosa revealed that they were also present within a specific cluster with the exception of one gene encoding the alpha-hydroxylase Ahd1, necessary for alpha-hydroxylation of the fatty acid. On the other hand, the flocculosin gene cluster contained an additional gene encoding an acetyl-transferase, probably involved in the acetylation of a further acetyl-group at the cellobiose moiety. It has already been shown that the presence of powdery mildew on a plant leaf triggers strong growth of P. flocculosa thereby affecting the pathogen. It remains to be elucidated which role flocculosin plays in this biocontrol activity. One hypothesis is that the release of flocculosin leads to formation of lesions in the membrane of the pathogen cells followed by the release of nutrients stimulating growth of the BCA. To validate this hypothesis, we are currently trying to generate a mutant strain deficient in its ability to produce flocculosin in order to analyze the biocontrol potential of the resulting phenotype.
Evaluation of basil (Ocimum spp.) cultivars and breeding lines for susceptibility to downy mildewA. WYENANDT (2), J. Simon (1), C. Park (3)(1) Director, New Use Agriculture and Natural Plant Products Program (NUANPP), Department of Plant Biology and Plant Pathology, Rutgers University, New Brunswick, NJ, USA; (2) Extension Specialist in Vegetable Pathology, Department of Plant Biology and Plant Pathology, Rutgers University, Bridgeton, NJ, USA; (3) Research Associate, New Use Agriculture and Natural Plant Products Program (NUANPP), Department of Plant Biology and Plant Pathology, Rutgers University, New Brunswick, NJ, USAPhytopathology 100:S198
Since 2007, downy mildew (Peronospora belbahrii) on sweet basil (Ocimum basilicum) has caused significant losses in New Jersey and other basil production areas of the eastern U.S. No known resistance in basil to downy mildew has been reported. In 2008, different basil species, cultivars, and Rutgers University breeding lines (30 in total) were evaluated for susceptibility to downy mildew in a field trial in southern New Jersey. On 27 Jul, all basil was hand transplanted in a randomized complete block design with four replications. The field was artificially-infested with downy mildew by transplanting infected sweet basil plants into rows on 31 Jul. On 20 Aug and 21 Sep basil plants were rated for downy mildew infection using a plus scale rating system. Ocimum basilicum was the most susceptible among all O. species and varieties evaluated. While sporulation ratings varied among the sweet basil varieties, popular commercial cultivars such as ‘Martina’, ‘Nufar’ and ‘Poppy Joe’s’ were among the most susceptible. Symptoms and sporulation on Ocimum × citriodorum and O. americanum cultivars were present, but far less than on O. basilicum cultivars. ‘Spice’, ‘Blue Spice’, and ‘Blue Spice Fil’ were the least susceptible to basil downy mildew with no visible symptoms developing on the leaves. Similar findings were observed on a second but non-inoculated basil cultivar trial in northern New Jersey. This is the first report of potential resistance in Ocimum spp. to downy mildew. Observations from this study show that genetic resistance is possible. Selection criteria such as foliar morphology, plant architecture, as well as, the presence of secondary metabolites are being examined as potential avenues for developing downy mildew resistance basil cultivars.
Wetwood – An ignored corner in forest pathologyD. YANG (1)(1) FPInnovations-Forintek Division, 319 rue Franquet, Quebec, QC, Canada, G1P 4R4Phytopathology 100:S198
Wetwood, or water pocket, is caused by anaerobic bacteria and occurs in many softwood and hardwood species. The bacteria enter trees through wounds or roots and produce pectinolytic enzymes to destroy the vessel and ray pit membranes of wood. The reproduction and metabolites of these bacteria form a foetid liquid in wood, which results in a high moisture content (MC) of the wetwood. Because the MC of wetwood is much higher than average, wetwood usually requires relatively long periods for adequate drying in sawmill. Degradation of pectic substances of the middle lamella causes weakness in the chemical bonds between wood cells. Consequently, weak bonding increases the risk of warping and checking in lumber during drying process. Wetwood also has a lower permeability than normal wood; this, in turn, affects the wood’s treatability with preservatives. The economic losses resulting from wetwood for wood production and utilization are enormous. Many studies have been conducted in sawmill on drying wetwood using various physical, chemical, biological or mechanical methods, but the problem has yet to be solved. Studies on wetwood infection mechanisms and its control measurements in forest are limited. More attention should be given to wetwood problem, and wetwood-free trees are required for lumber manufacturing and wood utilization.