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The crop pathogen Fusarium graminearum often colonizes non-cultivated grasses, but the phenotypic variation found in isolates recovered from these hosts has not been thoroughly investigated or compared to that observed in isolates collected from crop hosts. Fusarium graminearum growth, perithecia formation, and virulence on crops (maize seedlings, wheat seedlings, wheat spikes) were measured in laboratory and greenhouse experiments using isolates (n = 24) recovered from three non-cultivated grasses (Bromus inermis, Dactylis glomerata, and Phalaris arundinacea) and winter wheat (Triticum aestivum) found at a single research farm in northeastern New York. While individual isolates varied significantly for all phenotypes measured, grass and wheat derived isolates displayed a comparable range of phenotypic values. Trichothecene genotypes were determined from the TRI12 and TRI1 loci, and mycotoxin production was quantified in mature wheat spikes. Trichothecene genotype and phenotype were largely concordant and were not related to isolate source. These findings support consideration of non-cultivated hosts as sources of diverse pathogen inoculum that may cause crop disease.

The movement of plant pathogens between cultivated and natural host communities can result in lost agricultural production and altered microbial or plant biodiversity. Fusarium graminearum incidence was studied in wild grass hosts for 3 years to better understand the ecology of this plant pathogen at the interface of crop fields and nonagricultural environments. Research sites (n = 23) were spread between regions of high and low agricultural production and included both agricultural and nonagricultural fields. Pathogen incidence in living grass spikes and senesced, overwintered stems varied between regions of New York and was lowest in a region with sparser agricultural production (P = 0.001). However, pathogen incidence within regions was similar at both agricultural and nonagricultural sites. The groundcover of crop and wild hosts within 1 km of sample sites were equally effective predictors of pathogen incidence, indicating either host group may drive pathogen spread. Rainfall in the 8 weeks preceding sample collection was strongly correlated with F. graminearum incidence in grasses, as well as an increased prevalence of F. graminearum in Fusarium spp. communities (P = 0.001). Grass species diversity was not associated with a reduction in pathogen incidence, and F. graminearum incidence did not vary among the most well-sampled grasses. These results indicate the pathogen colonizes and spreads in noncultivated grasses in a manner consistent with existing concepts of pathogen epidemiology in cereal crops. Increasing host acreage, whether cultivated or not, could drive the colonization of grasses in remote or protected environments, potentially altering their microbial communities.

Crown rust is the principal disease of spring oat in New York. Management with resistance genes is effective but contingent on understanding varietal responses to local pathogen populations. Field studies were conducted from 2015 to 2018 to assess the crown rust susceptibility of commercial cultivars and public breeding lines under natural conditions in New York. Three of the 10 commercial varieties trialed were determined to be resistant, and breeding lines from five different states also exhibited resistance. On average, yield was reduced by 34.56 kg/ha for every 1% increase in crown rust severity, whereas the impact on test weight was negligible. A race differential panel was deployed in 2018 at a central screening nursery to determine the range of pathogen virulence present. Susceptible interactions were observed on only five crown rust differentials, and virulence on all five has been recorded at high levels across the country. Crown rust may be a limiting factor to oat production in New York, but yield potential and crop value can be preserved by planting an appropriately resistant variety.

Fusarium graminearum is primarily understood as an agricultural pathogen affecting cereal crops, but its host range also includes diverse, noncultivated grasses ubiquitous across agricultural and natural environments. Wild grasses may select for the production of diverse toxin variants (chemotypes) and serve as reservoirs of genetic diversity or sources of disease-inciting inoculum. Populations at the intersection of wheat and wild grass communities were described using 909 isolates collected from wheat spikes, wild grass spikes, and overwintered wild grass stems found at natural and agricultural sites in regions of high and low crop production. Trichothecene (TRI) genotypes correlated to pathogen chemotype were predicted from two loci, and multilocus genotypes (MLGs) were determined using eight microsatellite loci. The genetic diversity of wild grass and wheat-derived populations was comparable, and their differentiation was low. Duplicate MLGs were rare even in samples collected from a single square meter, although they could be found in multiple hosts, environments, regions, and years. TRI genotype frequencies differed between region and land use. Admixture between TRI genotype-defined populations, which correspond to three previously described sympatric North American populations, was detected and was highest in a region with remote host communities and little agricultural production. Nonagricultural environments may maintain different pathogen TRI genotypes than wheat fields and provide an opportunity for recombination between isolates from different F. graminearum populations. A lack of structural barriers suggests that pathogen gene flow is uninhibited between wheat and wild grass communities, and the recovery of putative clones from multiple hosts and environments provides initial evidence that noncultivated grasses are a source of local and regional inoculum.

Switchgrass (Panicum virgatum L.) is a biomass candidate crop which has been improved for yield, but disease resistance development has largely been ignored. Bipolaris oryzae (Breda de Haan) Shoemaker can cause Bipolaris seed rot, reducing seedling establishment, and Bipolaris leaf spot, reducing biomass yield. In order to initiate a breeding program, heritability based on half-sib progenies of the disease resistance were conducted in 47 half-sib progenies of lowland ‘Kanlow’ and upland ‘Cave-in-Rock’. Test crosses of progenies from resistant and susceptible parents in upland ‘Shelter’ and Cave-in-Rock were conducted to determine genetic control of resistance to Bipolaris leaf spot. To breed for resistance to two diseases, two cycles of recurrent phenotypic selection were done separately in Shelter and Cave-in-Rock at 10% selection intensity. As a result, resistance to Bipolaris seed rot showed moderate to high heritability (0.33 ± 0.16 to 0.83 ± 0.09) in both individual- and half-sib-based computations, reflecting actual genetic gain (44.5–125.3%) from two cycles of selections. However, resistance to Bipolaris leaf spot showed non-significant heritability (0.02 ± 0.06 to 0.19 ± 0.19) and non-significant progress of selection for the trait. Results from test crosses suggested that the resistance was not controlled by R genes but possibly was quantitatively inherited by many alleles with small effects. Such a difference in the gains resulted in non-significant correlation between two resistances. Due to high progress in selection resistance to Bipolaris seed rot, the screening method for resistance can be integrated to existing breeding programs.

In addition to causing disease in wheat and other grain crops, Fusarium graminearum is associated with a wide range of forage, weedy and non-cultivated gramineous species.. The nature of these asso...

Pathogens play an important role in the evolution of plant populations, but genetic mechanisms underlying disease resistance may differ greatly between geographic areas as well as over time. Local adaptation is thought to be an important step in plant evolution, and may be impacted by differential pathogen pressures in concert with abiotic factors. This study uses locally adapted ecotypes of the native perennial switchgrass (Panicum virgatum) to examine the temporal and spatial variation in the genetic architecture of resistance to fungal pathogens, namely switchgrass leaf rust (Puccinia novopanici). To identify loci underlying variation in pathogen resistance in switchgrass, we scored rust damage across an outcrossed mapping population at eight locations across the central United States from southern Texas to Michigan. We followed rust progression at these sites for three years and mapped quantitative trait loci (QTLs) using function-valued transformations of rust progression curves. Overall, we mapped 51 QTLs that varied in presence and strength over the three-year period. Two large-effect QTLs were consistently associated with variation in rust progression in multiple sites and years, and are therefore potentially the result of the same underlying resistance genes. Interestingly, these two large-effect QTLs were almost exclusively detected in northern sites. This pattern could be caused by geographic difference in genetic architecture. The distribution of rust strains or variation in climatic conditions across the field sites could result in genotype-by-environment interactions in efficacy of rust resistance loci. Beyond reducing rust damage by 34%, the beneficial alleles at the two loci also increased biomass by 44%, suggesting a direct benefit by pleiotropy or indirect benefit through genetic linkage. Our results suggest an important role for fungal pathogens in the local adaptation of switchgrass and illustrate an influential geographic component of the genetic architecture of plant disease resistance.

The main techniques for minimizing Fusarium head blight (FHB, or scab) and deoxynivalenol in wheat and barley are well established and generally available: planting of moderately FHB-resistant cultivars, risk monitoring, and timely use of the most effective fungicides. Yet the adoption of these techniques remains uneven across the FHB-prone portions of the U.S. cereal production area. A national survey was undertaken by the U.S. Wheat and Barley Scab Initiative in 17 states where six market classes of wheat and barley are grown. In 2014, 5,107 usable responses were obtained. The highest percentages reporting losses attributable to FHB in the previous 5 years were in North Dakota, Maryland, Kentucky, and states bordering the Great Lakes but across all states, ≥75% of respondents reported no FHB-related losses in the previous 5 years. Adoption of cultivar resistance was uneven by state and market class and was low except among hard red spring wheat growers. In 13 states, a majority of respondents had not applied an FHB-targeted fungicide in the previous 5 years. Although the primary FHB information source varied by state, crop consultants were considered to be an important source or their primary source of information on risk or management of FHB by the largest percentage of respondents. Use of an FHB risk forecasting website was about twice as high in North Dakota as the 17-state average of 6%. The most frequently cited barriers to adopting FHB management practices were weather or logistics preventing timely fungicide application, difficulty in determining flowering timing for fungicide applications, and the impracticality of FHB-reducing rotations. The results highlight the challenges of managing an episodically damaging crop disease and point to specific areas for improvement.

Seed of soft white winter wheat collected from New York regional cultivar trials in 1995 and 1996 were assayed on an agar medium selective for Stagonospora nodorum. Incidence of seed infection varied with production environment. Relative incidence of seed infection differed significantly among cultivars and was consistent across environments. The flag leaves and ears of 12 cultivars were inoculated quantitatively at flowering in a glasshouse. Cultivars did not differ significantly in disease on the flag leaves. Incidence of seed infection for all cultivars was above 60%, but was significantly lower in Delaware and Houser than in other cultivars. Results confirm that wheat cultivars differ in their relative susceptibility to seed infection by S. nodorum. Resistance in wheat to seed infection by S. nodorum may be a useful mechanism for reducing initial inoculum in areas where infected seed is considered the primary inoculum source for Stagonospora nodorum blotch.

Brown root rot (BRR), caused by the fungal pathogen Phoma sclerotioides G. Preuss ex Sacc. (synonym Plenodomus meliloti Dearn. & G.B. Sanford), is associated with winterkill, slow emergence from winter dormancy, and yield loss of alfalfa (Medicago sativa L.) (1,2). BRR is a problem in regions with severe winters and is common in Alaska and Alberta, Saskatchewan and Manitoba, Canada. It was first observed in the continental United States in Wyoming during 1996 (2) and has subsequently been found in Idaho, Minnesota, Montana, New Hampshire, New York, Vermont, and Wisconsin. In the intermountain valleys of northern New Mexico and western Colorado, winters can be severe; alfalfa winterkill events occur periodically, but it is unknown if BRR is present. In May 2006, alfalfa plants were collected from production fields in Huerfano, Otero, and Rio Grande counties in Colorado and Rio Arriba and Taos counties in New Mexico and assessed for BRR. Two to three fields were sampled per county and 20 or 40 plants were collected per field. All fields existed for at least two winters. Fields sampled in Rio Grande County exhibited severe winterkill, with most plants completely girdled by crown lesions. Plants from other fields exhibited a range of root and crown rots. Isolation of P. sclerotioides was attempted from all plants with a previously described protocol (4). The pathogen was isolated from crown lesions of one alfalfa plant each from Rio Grande and Taos counties. Both lesions extended into the cortex. On potato dextrose agar and water agar with barley (4), single-conidium cultures of each isolate produced large pycnidia (0.35 to 0.80 mm in diameter) with multiple beaks, white cirri darkening to yellow with age, and unicellular, hyaline, ovoid conidia 5 to 7 μm long by 2 μm wide. Diagnostic PCR of the cultures using P. sclerotioides-specific primers (3) resulted in a single amplicon of expected size (500 bp). The internal transcribed spacer (ITS) 1, 5.8S, and ITS2 of the rDNA were amplified and sequenced using primers ITS1 and ITS4. The ITS sequences (GenBank Accession Nos. EU265669 and EU265670) were >98% identical to P. sclerotioides ATCC isolate 56515 over 503 bp of aligned sequence. Potted ‘Vernal’ alfalfa was inoculated 4 months after seeding, kept at 4°C for 5.5 weeks, 0 to –2°C for 12 weeks, and 4°C for 3 weeks. Of the 14 plants inoculated with the Colorado isolate, 11 developed cortical lesions and 8 winterkilled. Of the 23 plants inoculated with the New Mexico isolate, 22 developed cortical lesions and 16 winterkilled. Lesions were light to very dark brown, sometimes with a darker border and often containing abundant pycnidia. Winterkill was associated with lesions girdling the crown. P. sclerotioides was isolated from the lesions. To our knowledge, this is the southernmost report of BRR in North America and the first report of BRR in New Mexico and Colorado. The incidence and severity of BRR in the region surveyed appear to be considerably lower than in the more northern regions. References: (1) B. Berkenkamp et al. Can. J. Plant Sci. 71:211, 1991. (2) C. R. Hollingsworth et al. Can. J. Plant Pathol. 25:215, 2003. (3) R. C. Larsen et al. Plant Dis. 86:928, 2002. (4) M. J. Wunsch et al. Plant Dis. 91:1293, 2007.

Knowledge of the movement of Gibberella zeae (Fusarium graminearum) from a local source of inoculum in infested cereal debris is critical to the management of Fusarium head blight (FHB) of wheat. Previous spatial dissemination and infection studies were unable to completely distinguish the contributions of released inocula from those of background inocula. Clones of G. zeae were released and recaptured in five wheat fields in New York and Virginia in 2007 and 2008. Amplified fragment length polymorphisms were used to track and unambiguously identify the released clones in heterogeneous populations of the fungus recovered from infected wheat spikes collected at 0, 3, 6, and ≥24 m from small-area sources of infested corn residues. The percent recovery of the released clones decreased significantly at fairly short distances from the inoculum sources. Isolates of G. zeae recovered at 0, 3, 6, and ≥24 m from the center of source areas shared 65, 19, 13, and 5% of the genotypes of the released clones, respectively. More importantly, the incidence of spike infection attributable to released clones averaged 15, 2, 1, and

Switchgrass (Panicum virgatum L.) is a native perennial grass with potential as a biofuel crop. The smut fungus, Tilletia maclaganii (Berk.) Clint., is associated with significant biomass reduction in switchgrass in the Midwest (4), but has not been reported in the northeast United States in more than 60 years (New York in 1890 and Pennsylvania in 1946) (2,3). From 2007 to 2010, smutted panicles were observed on the majority of plants in stands of several switchgrass cultivars at the USDA-NRCS Plant Materials Center in Big Flats (Chemung County), NY; in production fields of several switchgrass cultivars near Meadville (Crawford County), PA; and in an ornamental bed of switchgrass in Ithaca (Tompkins County), NY. Smutted panicles emerged 3 to 4 weeks prior to healthy panicles, had a compact, club-shaped appearance, and enlarged florets with swollen ovaries that readily released a powdery mass of odorless, rusty orange-to-dark brown teliospores when pinched. The entire caryopsis of every floret within a panicle was smutted and the infected plants appeared stunted, indicative of systemic infection. The fungus from each location was identified as T. maclaganii based on host, habit, and teliospore morphology (3). Teliospores were pale yellowish brown to reddish brown, varied from globose to slightly irregular in shape, and averaged 21 μm (18 to 25 μm) in diameter. The exospore was thick (2 to 3 μm), finely verrucose, and no sheath was present. True sterile cells, pale yellow and 10 to 18 μm in diameter, were sparsely present. Teliospores germinated and formed large (40 to 60 × 3 to 6 μm), nonconjugating basidiospores within 20 h on 2% water agar (WA). Occasionally, we also found the floret-infecting species T. pulcherrima (1) on switchgrass at very low incidence in Big Flats, NY, but it was easily distinguished from T. maclaganii. Stratified seeds (3 g) of ‘Shelter’, washed and found to be free of teliospores, were dusted with 0.04 g of teliospores of T. maclaganii isolate Tm001NY09 (Cornell Plant Pathology Herbarium Accession CUP-67931) harvested from infected ‘Shelter’ in Big Flats, NY in 2009. Inoculated and noninoculated seeds were sown in seedling trays, transplanted, and evaluated at panicle emergence. There were no symptoms on plants from noninoculated seeds. Symptoms on inoculated plants were consistent with field observations and teliospores were reisolated from infected panicles and cultured on 2% WA. Teliospores harvested from a single panicle infected with Tm001NY09 were used for culturing and DNA extraction. The fully annotated sequence of the rDNA internal transcribed spacer and 5.8S regions of this isolate were deposited in GenBank (Accession No. JF745116). Smut outbreaks in New York and Pennsylvania suggest that T. maclaganii must be managed effectively if switchgrass production is to be sustainable in the Northeast. References: (1) L. M. Carris et al. Plant Dis. 92:1707, 2008. (2) R. Durán and G. W. Fischer. The Genus Tilletia. Washington State University, Pullman, WA, 1961. (3) D. F. Farr and A. Y. Rossman. Fungal Databases. Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved from http://nt.ars-grin.gov/fungaldatabases/ , May 3, 2011 (4) P. M. Thomsen et al. Online publication. doi:10.1094/PHP-2008-0317-01-RS. Plant Health Progress, 2008.

Wheat and barley are critical food and feed crops around the world. Wheat is grown on more land area worldwide than any other crop. In the United States, production of wheat and barley contributes to domestic food and feed use, and contributes to the export market and balance of trade. Fifteen years ago, Plant Disease published a feature article titled “Scab of wheat and barley: A re-emerging disease of devastating impact”. That article described the series of severe Fusarium head blight (FHB) epidemics that occurred in the United States and Canada, primarily from 1991 through 1996, with emphasis on the unparalleled economic and sociological impacts caused by the 1993 FHB epidemic in spring grains in the Northern Great Plains region. Earlier publications had dealt with the scope and damage caused by this disease in the United States, Canada, Europe, and China. Reviews published after 1997 further described this disease and its impact on North American grain production in the 1990s. This article reviews the disease and documents the information on U.S. FHB epidemics since 1997. The primary goal of this article is to summarize a sustained, coordinated, and collaborative research program that was put in place shortly after the 1993 epidemic, a program intended to quickly lead to improved management strategies and outreach implementation. This program serves as a model to deal with other emerging plant disease threats.

The estimated potential yield losses caused by plant pathogens is up to 16% globally and most research in plant pathology aims to reduce yield loss in our crops directly or indirectly. Yield losses caused by a certain disease depend not only on disease severity, but also on the weather factors, the pathogen’s aggressiveness, and the ability of the crop to compensate for reduced photosynthetic area. The yield loss-disease relationship in a certain host-pathogen system might therefore change from year to year, making predictions for yield loss very difficult at the regional or even at the farmer’s level. However, estimating yield losses is essential to determine disease management thresholds at which acute control measures such as fungicide applications, or strategic measures such as crop rotation or use of resistant cultivars are economically and environmentally sensible. Legislation in many countries enforces implementation of integrated pest management (IPM), based on economic thresholds at which the costs due to a disease justify the costs for its management. Without a better understanding of the relationship between disease epidemiology and yield loss, we remain insufficiently equipped to design adequate IPM strategies that will be widely adapted in agriculture. Crop loss studies are resource demanding and difficult to interpret for one particular disease, as crops are usually not invaded by only one pest or pathogen at a time. Combining our knowledge on disease epidemiology, crop physiology, yield development, damage mechanisms involved, and the effect of management practices can help us to increase our understanding of the disease-crop loss relationship. The main aim of this paper is to review and analyze the literature on a representative host-pathogen relationship in an important staple food crop to identify knowledge gaps and research areas to better assess yield loss and design management strategies based on economic thresholds.

The first large-scale survey of Fusarium head blight (FHB) in commercial wheat fields in southern Brazil was conducted over three years (2009 to 2011). The objectives were to: (i) evaluate whether increased FHB risk is associated with within-field maize residue; (ii) determine the spatial pattern of FHB incidence; and (iii) quantify the relationship between FHB incidence and severity. FHB was assessed in a total of 160 fields between early milk and dough. Incidence ranged from 1.0 to 89.9% (median = 25%) and severity from 0.02 to 18.6% (median = 1.3%). FHB risk was neither lower nor higher in wheat following maize than in wheat following soybean. Only 18% of fields were classified as having aggregated patterns of FHB-symptomatic spikes. A binary power law description of the variances was consistent with an overall random pattern of the disease. These results conform with the hypothesis that FHB epidemics in southern Brazil are driven by sufficient atmospherically-transported inoculum from regional sources. The incidence-severity relationship was coherent across growing season, growth stage, and previous crop; one common fitted curve described the relationship across all observations. Estimating severity from incidence may be useful in reducing the workload in epidemiological surveys.

In order to test the hypothesis that the trichothecene genotype composition of local populations of Fusarium graminearum is structured by specific habitats, a collection of 1,407 isolates was obtained from overwintered maize stubble, mature maize ears and wheat spikes, and the atmosphere 1.5 m aboveground during the flowering stage of these crops. These isolates were sampled at three diverse agricultural locations in New York State: namely, Aurora (sampled in 2012 and 2013) in central New York, Belmont (sampled in 2013) in southwestern New York, and Willsboro (sampled in 2013) in northeastern New York. Approximately 100 isolates of F. graminearum from each habitat were collected within a 10-mile2 area in each location. Polymerase chain reaction assays were used to identify three main B-trichothecene genotypes—3-acetyldeoxynivalenol (3-ADON), 15-ADON, or nivalenol (NIV)—based on amplification of portions of Tri3 and Tri12 genes. All but the NIV genotype were detected. The 15-ADON genotype predominated in most locations; frequencies were 92% (652/709) at Aurora, 78% (332/379) at Belmont, and 53% (167/319) at Willsboro. Frequencies of any genotype did not differ in general among the four habits in each location. An exception was in Aurora 2012, where only 5 in 24 3-ADON isolates were found in samplings from the air and grains of both crops. As viewed by the composition of trichothecene genotypes, local populations of F. graminearum appear not to be structured by these four habitats inclusive of pathogenic and saprophytic phases of the fungus life cycle. The similar frequency of 3-ADON and 15-ADON in eastern New York (Willsboro), which is less than 400 km away from the Aurora sampling location in the central area of the state, suggests that regional populations may be differentiated based on selection associated with climatic or landscape features not currently identified.

Existing crop monitoring programs determine the incidence and distribution of plant diseases and pathogens and assess the damage caused within a crop production region. These programs have traditionally used observed or predicted disease and pathogen data and environmental information to prescribe management practices that minimize crop loss. Monitoring programs are especially important for crops with broad geographic distribution or for diseases that can cause rapid and great economic losses. Successful monitoring programs have been developed for several plant diseases, including downy mildew of cucurbits, Fusarium head blight of wheat, potato late blight, and rusts of cereal crops. A recent example of a successful disease-monitoring program for an economically important crop is the soybean rust (SBR) monitoring effort within North America. SBR, caused by the fungus Phakopsora pachyrhizi, was first identified in the continental United States in November 2004. SBR causes moderate to severe yield losses globally. The fungus produces foliar lesions on soybean (Glycine max) and other legume hosts. P. pachyrhizi diverts nutrients from the host to its own growth and reproduction. The lesions also reduce photosynthetic area. Uredinia rupture the host epidermis and diminish stomatal regulation of transpiration to cause tissue desiccation and premature defoliation. Severe soybean yield losses can occur if plants defoliate during the mid-reproductive growth stages. The rapid response to the threat of SBR in North America resulted in an unprecedented amount of information dissemination and the development of a real-time, publicly available monitoring and prediction system known as the Soybean Rust-Pest Information Platform for Extension and Education (SBR-PIPE). The objectives of this article are (i) to highlight the successful response effort to SBR in North America, and (ii) to introduce researchers to the quantity and type of data generated by SBR-PIPE. Data from this system may now be used to answer questions about the biology, ecology, and epidemiology of an important pathogen and disease of soybean.

Long range atmospheric transport is an important pathway for the spread of plant pathogens, such as rust fungi which can devastate cereal crop health and food security worldwide. In recent years, serious concern has been caused by the evolution of new virulent races of Puccinia graminis f. sp. tritici, a pathogen causing wheat stem rust that can result in close to 100% yield losses on susceptible wheat cultivars in favourable weather conditions. We applied an Earth system model to compare the suitability of the current climate and a business-as-usual climate scenario (RCP 8.5) for 2100 for wheat stem rust. Although there are large uncertainties in modelling changes in disease spread, we focus in this paper on the changes which are likely to be robust to model assumptions. We show that the warmer climate with lower relative humidity and enhanced turbulence will lead to ∼40% increase in the urediniospore emitting potential of an infected field as global average. The main predicted changes in the atmospheric long-range transport include reduced connections between Europe, Africa and South Asia, and increased frequency of spores crossing the mid-latitude oceans. Due to reduction in subfreezing conditions, the overwintering areas of the fungus will expand. On the other hand, projected drier conditions will reduce substantially the probability of an infection starting from deposited spores, except in irrigated fields.

Current knowledge of the aerobiology of Fusarium graminearum sensu lato is based on decades of published research documenting the processes of spore discharge, atmospheric transport, and deposition in this important pathogen of cereal crops worldwide. Spores from both local and more distant sources have been shown to cause infection in susceptible cereal crops when environmental conditions are favorable. Susceptible crops may be exposed throughout a growing season to airborne spores deposited in rain events and in night-time hours through gravitational settling. Given that spores deposited on cereal florets originate from distant as well as local sources, disease risk forecasts, based currently on weather favoring local spore production during the days before peak infection (i.e., initiation of crop flowering), might be improved by placing greater emphasis on local weather directly favoring infection at and following the time of flowering. Also, considering the genetic diversity of fungal spores introduced to local agricultural fields following atmospheric transport, crop breeders should select resistant varieties based on screening against a set of fungal isolates that represent the range of virulence observed in fungal populations across a broader geographic region. An increased understanding of the aerobiology of F. graminearum contributes to the overall knowledge of plant pathogen transport in the atmosphere.

Fusarium wilt (caused by Fusarium oxysporum f. sp. loti) is a serious disease of birdsfoot trefoil, Lotus corniculatus L., reducing yield of forage and seed. In the early 1990s a breeding program was begun to breed a Fusarium wilt-resistant birdsfoot trefoil. Our objectives were to (i) determine progress from recurrent phenotypic selection for resistance to Fusarium wilt in six birdsfoot trefoil populations and (ii) compare forage yield and persistence of Fusarium wilt-resistant populations to unselected populations in fi eld trials. Recurrent phenotypic selection was effective in improving resistance in the greenhouse, with mean improvement of 35% across all populations after three cycles of selection. In a fi eld with high natural disease pressure, a population developed after two cycles of selection for resistance had lower levels of disease incidence and yielded 1.33 Mg ha −1 more than the mean of nine cultivars in the seeding year. The Fusarium wilt-resistant population had 52% higher plant stand than the mean of the other cultivars at the end of the fi rst production year. In a trial inoculated with the Fusarium wilt organism, two cycle 3 populations averaged 28% more yield by June of the fourth production year and 22 more plants per m 2 than the mean of the unselected populations. Birdsfoot trefoil with resistance to Fusarium wilt yielded more and persisted longer than other cultivars under Fusarium wilt-infested fi eld conditions.

Fusarium head blight is a major concern for wheat production worldwide. The fungi that cause the disease may infect head tissues from flowering to late stages of kernel development, but a better understanding of the influence of the time of infection on grain weight reduction and mycotoxin accumulation resulting from the infection process is needed. We investigated the influence of wheat reproductive stage at the time of inoculation on disease and grain quality parameters, especially production of deoxynivalenol (DON) in mature grains. Heads of Norm wheat were spray inoculated with a macroconidial suspension of a DON-producing isolate of Fusarium graminearum at each of six reproductive stages from flowering to hard dough. Plants were incubated in a mist chamber for 48 h and then moved to the greenhouse until maturity. Norm wheat was susceptible at all stages inoculated but the highest grain weight reduction and DON accumulation occurred in plants inoculated past flowering to late milk stages. However, high incidences of kernel infection and significant levels of DON accumulation resulted from inoculations as late as the hard dough stage, even though there was no corresponding reduction in grain weight compared to non-inoculated plants. The occurrence of commercially significant levels of DON in plump, high-yielding wheat may result from infections that occur during favourable environments well after the flowering stages. Late infection and DON production should therefore be a future research focus for wheat breeding and integrated management of FHB and an important consideration for grading systems that employ the presence of visibly damaged kernels as a means of estimating DON content of wheat.

Schmale, D. G., III, Leslie, J. F., Zeller, K. A., Saleh, A. A., Shields, E. J., and Bergstrom, G. C. 2006. Genetic structure of atmospheric populations of Gibberella zeae. Phytopathology 96:1021-1026. Gibberella zeae, causal agent of Fusarium head blight (FHB) of wheat and barley and Gibberella ear rot (GER) of corn, may be transported over long distances in the atmosphere. Epidemics of FHB and GER may be initiated by regional atmospheric sources of inoculum of G. zeae; however, little is known about the origin of inoculum for these epidemics. We tested the hypothesis that atmospheric populations of G. zeae are genetically diverse by determining the genetic structure of New York atmospheric populations (NYAPs) of G. zeae, and comparing them with populations of G. zeae collected from seven different states in the northern United States. Viable, airborne spores of G. zeae were collected in rotational (lacking any apparent within-field inoculum sources of G. zeae) wheat and corn fields in Aurora, NY in May through August over 3 years (2002 to 2004). We evaluated 23 amplified fragment length polymorphism (AFLP) loci in 780 isolates of G. zeae. Normalized genotypic diversity was high (ranging from 0.91 to 1.0) in NYAPs of G. zeae, and nearly all of the isolates in each of the populations represented unique AFLP haplotypes. Pairwise calculations of Nei’s unbiased genetic identity were uniformly high (>0.99) for all of the possible NYAP comparisons. Although the NYAPs were genotypically diverse, they were genetically similar and potentially part of a large, interbreeding population of G. zeae in North America. Estimates of the fixation index (GST) and the effective migration rate (Nm) for the NYAPs indicated significant genetic exchange among populations. Relatively low levels of linkage disequilibrium in the NYAPs suggest that outcrossing is common and that the populations are not a result of a recent bottleneck or invasion. When NYAPs were compared with those collected across the United States, the observed genetic identities between the populations ranged from 0.92 to 0.99. However, there was a significant negative correlation (R = –0.59, P < 0.001) between genetic identity and geographic distance, suggesting that some genetic isolation may occur on a continental scale. The contribution of long-distance transport of G. zeae to regional epidemics of FHB and GER remains unclear, but the diverse atmospheric populations of G. zeae suggest that inoculum may originate from multiple locations over large geographic distances. Practically, the long-distance transport of G. zeae suggests that management of inoculum sources on a local scale, unless performed over extensive production areas, will not be completely effective for the management of FHB and GER.

Once Wheat spindle streak mosaic virus (WSSMV) becomes established in a field, the only available control strategy is the planting of resistant genotypes. In this study, we assessed 112 genotypes of winter wheat, rye, triticale, and barley for resistance to WSSMV in a 3-year trial in a field that had been used continuously for WSSMV evaluation for over 20 years. Because resistance to WSSMV reduces the percentage of plants that develop detectable virus titer and symptoms, we collected and analyzed disease incidence data. None of the genotypes was immune to infection. Sixty-two of the regionally adapted genotypes repeatedly expressed resistance to WSSMV, thus providing growers with a choice of cultivars resistant to WSSMV. Because of a significant interaction between genotypes and environment (year), genotypes should be assessed for incidence of symptomatic plants in multiple years, particularly when differentiating intermediate responses from highly susceptible and highly resistant responses.

Many fungal plant pathogens rely on atmospheric motion systems for transport. The movement of these pathogens in the atmosphere is characterized by processes of liberation, drift, and deposition. We observed temporal patterns of viable spore deposition of Gibberella zeae, causal agent of fusarium head blight (FHB) of wheat, over rotational wheat fields (with no visible residues of corn or wheat, potential inoculum sources of G. zeae) in Aurora, New York, United States. Viable, airborne spores of G. zeae were collected on Petri plates containing selective medium placed 30 cm above wheat canopies. Over 40 000 viable spores of G. zeae were collected over a total of 73 day (6:00 am to 8:00 pm) or night (8:00 pm to 6:00 am) sampling periods in 3 years (2002, 2004, and 2005). The vast majority of the spores was collected at night (94% in 2002, 86% in 2004, and 82% in 2005). Viable spores were deposited in all but one sampling period spanning spike emergence through kernel milk stages of local wheat. Seven major...

Understanding the biological and meteorological interactions that direct the movement of airborne propagules of Gibberella zeae inside corn canopies is crucial to the epidemiology of gibberella ear rot. We observed the temporal patterns of viable spore deposition of G. zeae over two years (2002 and 2003) inside corn fields in Aurora, New York, United States. Viable, airborne propagules of G. zeae were collected inside corn canopies on Petri plates containing selective media placed at the level of receptive corn silks. Spores were deposited inside corn canopies during every day or night sampling period spanning the duration of silking in both years. In 2003, more than 91% of the colonies were collected during night-time sampling periods. On average, spore deposition was greater than 50 spores per plate for five sampling periods that occurred only at night. The cumulative exposure of corn silks to airborne spores of G. zeae should be considered in the development of risk models and management strategies for...

The soybean cyst nematode (SCN), Heterodera glycines Ichinohe, is the most damaging pathogen of soybean (Glycine max (L.) Merr.), causing more than $1 billion in yield losses annually in the United States (Allen et al. 2017). The SCN distribution map updated in 2014 showed that SCN were detected in all major soybean-producing states in the U.S. except West Virginia and New York (Tylka and Marett 2014). Soybean shows great economic promise in NY and its production area in the region has been expanding rapidly. In coordination with a statewide soybean disease survey, soil samples have been collected from seventeen counties throughout NY since 2013 to search for the presence of SCN. A post-harvest soil sample collected in the fall of 2016 from a soybean field in Cayuga County, NY, was processed using the sugar centrifugal-flotation method to extract nematodes and a few brown and lemon-shaped cysts, similar to those of SCN, were isolated. The lemon-shaped cysts were light to dark brown and had a zigzag patter...

In 2013, heads exhibiting characteristic Fusarium head blight (FHB) symptoms were collected from a field of winter malting barley (Hordeum vulgare L.) in Herkimer County. The heads were surface-sterilized in 95% ethanol for 1 min followed by 20% sodium hypochlorite for 1 min, then rinsed in sterile distilled water, and incubated on potato dextrose agar (PDA) amended with antibiotics for 7 days with a 12-h photoperiod under black light. All Fusarium colonies were transferred to PDA, and monosporic isolates were obtained. A PCR assay of the TRI12 region was used to determine the tricothecene genotype of each isolate (Ward et al. 2002). Two isolates were positive for the nivalenol (NIV) genotype, and upon further examination, the macroconidia of these two isolates were on average shorter and wider (31-52 x 3-4.5 µm) than those typical (35-62 x 2-2.5 μm) of isolates in the F. graminearum species complex, but in the range reported for F. cerealis (Leslie and Summerell 2002). Those two NIV isolates were then su...

Stagonospora nodorum blotch (SNB) often develops explosively on upper leaves and glumes of wheat. Inoculum for late season infections may arise from early disease foci in the lower canopy or from recent immigration of wind-dispersed ascospores. Research was conducted to determine if foci of SNB are present and secondary spread has occurred in fields before tiller elongation. We determined the incidence of infection by Stagonospora nodorum for plants sampled at the mid-tillering stage in 96 1-m2 quadrats in each of two fields. Isolates of S. nodorum were recovered from 32 quadrats, one per infected plant where possible. Multilocus restriction fragment length polymorphism haplotypes were determined for each isolate. Of 55 isolates collected from one field, there were 22 distinct haplotypes. Diseased plants were aggregated in both fields; aggregates sometimes extended to adjacent quadrats. Plants within aggregates were often infected by the same haplotype, suggesting that secondary spread had occurred. Foci overlapped because some aggregates were infected by more than one haplotype. Our results show that genetically diverse populations of S. nodorum were already established in fields before canopy development and were comprised of sometimes overlapping foci undergoing clonal expansion.

Wheat spindle streak mosaic bymovirus (WSSMV) causes an economically important disease of winter wheat in Europe and North America. Artificial inoculation with this virus to identify resistant wheat genotypes is difficult. This study was conducted to identify restriction fragment length polymorphism (RFLP) markers associated with resistance to this disease. A population, consisting of 104 F5 recombinant inbred lines from a cross between hexaploid Triticum aestivum cultivars 'Geneva' (resistant) and 'Augusta' (susceptible), was evaluated for WSSMV symptoms under field conditions for four years. Two linked markers on the long arm of chromosome 2D, Xbcd1095 and Xcdo373, were determined to be associated with WSSMV resistance by bulked segregant analysis of the 10 most resistant and 10 most susceptible lines. Marker Xcdo373 accounted for 79% and Xbcd1095 for 73% of the phenotypic variation. Our results suggest that resistance to WSSMV in this population is qualitative in nature and is controlled by few genes. These markers should be useful in the development of wheat cultivars resistant to WSSMV and perhaps also to wheat yellow mosaic bymovirus (WYMV).Key words: wheat, wheat spindle streak mosaic virus (WSSMV), RFLP markers, resistance, bymovirus, wheat yellow mosaic virus, barley yellow mosaic virus.

The USDA has a goal of implementing integrated pest management (IPM) practices on 75% of crop area by 2000. Growers require more economic information before adopting IPM practices. A field study was initiated in New York to evaluate weed control, yields, and net returns of chemical (broadcast herbicides), chemical-mechanical (handed herbicides and cultivations and mechanical (rotary hoe and cultivations) weed management under moldboard plow and chisel tillage in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. Chemical and chemical-mechanical weed management had similar corn net returns under moldboard plow ($370 and $355 ha -1 , respectively) and chisel tillage ($282 and $287 ha -1 ). Mechanical weed management had less net returns in moldboard plow ($302 ha -1 ) and chisel tillage ($121 ha -1 ) because of 15% lesser corn densities and greater weed densities, especially in chisel tillage. In soybean, mechanical weed management in moldboard plow tillage had similar weed density (1.5 weeds m 2 ) lower yield (2.71 Mg ha 1 ), but similar net return ($107.50 ha 1 ) compared with chemical (1.3 weeds m 2 . 2.92 Mg ha 1 , and $85.60 ha 1 , respectively) and chemical-mechanical weed management (1.0 weeds m 2 , 2.78 Mg ha 1 and $99.35 ha 1 , respectively). In chisel tillage, mechanical weed management had greater weed density (7.4 weeds m 2 ), lower yield (2.2 Mg ha 1 ), and lower net return (-$7.80 ha 1 ) compared with chemical (1.9 weeds m 2 , 2.8 Mg ha 1 , and $56.80 ha 1 , respectively) and chemical-mechanical weed management (1.9 weeds m 2 , 2.4 Mg ha 1 , and $27.30 ha 1 ). Corn and soybean growers apparently can adopt chemical-mechanical weed management and maintain net returns. Soybean growers who use moldboard plow tillage can also adopt mechanical weed management and maintain net returns.

Imidacloprid is a seed-applied nitroguanidine insecticide that has both contact and long-lasting systemic properties. Its direct effects on cereal aphid populations and indirect effects on barley yellow dwarf luteovirus (BYDV) incidence were examined in laboratory and field studies. Adult longevity and fecundity of three aphid species caged on various aged, imidacloprid-treated oat or wheat plants was reduced, although the quantitative efficacy of the compound differed among aphid species. The transmission efficiency of BYDV by aphids to imidacloprid-treated plants was lower, relative to nontreated plants, when plants were 10 days old, but similar to nontreated when plants were 24 days old. In three years of field trials using winter wheat and two years using spring oat, aphid populations were reduced significantly in imidacloprid-treated plots relative to nontreated plots. Although the number of alighting alate aphids did not differ significantly between imidacloprid-treated or nontreated plots, the number of apterous aphids remained significantly lower in the treated plots for the majority of the growing season. BYDV epidemics did not develop in spring oat in either of the two years. BYDV epidemics did develop in the fall in the emerging winter wheat crop. Rhopalosiphum maidis was the predominant aphid migrating into the 1991–1992 crop. The incidence of the BYDV-RMV serotype was three times higher in nontreated plots than in imidacloprid-treated plots. In the 1992–1993 and 1994–1995 seasons, R. maidis and R. padi were the predominant aphids migrating into the crop, although R. padi was the predominant colonizing aphid. The incidence of BYDV-RMV was similar in imidacloprid treated and nontreated plots in 1992–1993, but the incidence of the BYDV-PAV serotype was significantly less in the treated plots. In 1994–1995, the incidence of both BYDV-PAV and BYDV-RMV was higher in the nontreated plots than in the imidacloprid-treated plots. Imidacloprid offers several advantages both in terms of its long-lasting systemic activity and its mode of applicaiton. As a seed treatment, the amount of material applied is minimized, there is little waste and the environmental impacts are reduced. The effectiveness of the compound at reducing the fecundity or reproductive rate of several aphid species may be advantageous in controlling secondary spread of viruses. However, the contact properties of the compound, important in repelling aphids or preventing phloem feeding, may be short-lived, thus reducing its effectiveness in preventing primary spread of the virus into the crop, especially under high aphid and inoculum pressure.

Seed transmission ofPyrenophora tritici-repentis, a common foliar pathogen of wheat, was investigated in soft white winter wheat cv. Frankenmuth and found to be non-systemic; the emerging coleoptile was infected externally by hyphal growth from the infected pericarp. Hyphae from the infected coleoptile then infected the first and second seedling leaves as they emerged. Coleoptile symptoms ranged from tiny brown streaks or spots to large, brown necrotic areas accompanied by cracking and distortion of the coleoptile. Small brown spots sometimes occurred on the first and rarely on the second seedling leaves, often accompanied by leaf distortion. Pseudothecial initials of the fungus were present within or on the seed remnants. Seed transmission efficiency was as high as 92%in vitro and 60% in potting soil outdoors. Seed infection did not affect germinationin vitro, but slightly reduced emergence in potting soil. Seedling weight and height were reduced significantly. In potting soil, seed infection also resulted in delayed plant growth and increased tan spot severity at later stages of plant development. Under controlled conditions, seed transmission efficiency and incidence of pseudothecia on seed were negatively correlated with seed germination temperature in the range of 9 to 21 °C, whereas frequency of recovery of the fungus from symptomatic coleoptiles and leaves was positively correlated with seed germination temperature. These results suggest that infected seed may serve as a source of inoculum for tan spot epidemics and for dispersal of strains of the fungus to new areas.

Although Verticillium wilt (VW), caused by Verticillium alboatrum Reinke & Berth., has been considered a serious disease on alfalfa (Medicago sativa L.) in North America since 1976, little research has been done to determine both the effects on forage yield due to resistant cultivars and the necessary levels of resistance required to adequately protect the crop. In 1985, 16 cultivars were evaluated both for resistance after inoculation by the root-soak method in a growth chamber, and for yield and plant stand after seed inoculation in sward plots in the field in Ithaca, NY (...)

Cadle-Davidson, L., and Bergstrom, G. C. 2004. The effects of postplanting environment on the incidence of soilborne viral diseases in winter cereals. Phytopathology 94:527-534. Soilborne wheat mosaic virus (SBWMV) and Wheat spindle streak mosaic virus (WSSMV) are putatively transmitted to small grains by the obligate parasite Polymyxa graminis, but little is known about environmental requirements for transmission and the resulting disease incidence. We planted susceptible wheat and triticale cultivars in field nurseries on different autumn dates in 3 years and observed the incidence of symptomatic plants in each following spring. Autumn postplanting environment explained most of the variation in disease caused by both viruses. Little apparent transmission, based on eventual symptom development, of either virus occurred after the average soil temperature dropped below 7°C for the remainder of the winter. To forecast disease, we tested an SBWMV transmission model in the field, based on laboratory results, that predicts opportunities for transmission based on soil temperature and soil moisture being simultaneously conducive. This model was predictive of soilborne wheat mosaic in 2 of 3 years. Zoospores of P. graminis have optimal activity at temperatures similar to those in the SBWMV transmission model. Furthermore, the matric potential threshold (as it relates to waterfilled pore sizes) in the SBWMV transmission model fits well with P. graminis as vector given the size restrictions of P. graminis zoospores. Conditions optimal for SBWMV transmission in the laboratory were not conducive for WSSMV transmission in the laboratory or for wheat spindle streak mosaic development in the field. This differential response to environment after emergence, as indicated by disease symptoms, may be due to virus-specific environmental conditions required to establish systemic infection via the same vector. Alternatively, the differential response may have been due to the involvement of a different vector in our WSSMV nursery than in our SBWMV nursery. Our results suggest that, as a control tactic for SBWMV or WSSMV, earliness or lateness of planting is less important in determining virus transmission and disease than the specific postplanting environment. Improved models based on the postplanting environment might predict virus-induced losses of yield potential, and in some cases, growers might avoid purchase of spring inputs such as pesticides and fertilizer for fields with greatly reduced yield potential. Additional keywords: Bymovirus, Furovirus, Wheat soilborne mosaic virus.

Cadle-Davidson, L., Schindelbeck, R. R., van Es, H. M., Gray, S. M., and Bergstrom, G. C. 2003. Using air pressure cells to evaluate the effect of soil environment on the transmission of soilborne viruses of wheat. Phytopathology 93:1131-1136. An air pressure cell, a laboratory tool that precisely controls soil matric potential, was utilized in a novel approach to investigate the epidemiology and management of soilborne disease. Matric potentials of –1, –5, –20, and –40 kPa were established in cores of field soil infested with Wheat soilborne mosaic virus (WSBMV) and its presumed vector Polymyxa graminis. Equilibrated soil cores were planted to wheat (Triticum aestivum), and after intervals of growth under controlled environment, virus transmission was assessed by serological detection of the virus in washed roots. Transmission occurred at all but the driest soil matric potential tested, –40 kPa, in which only pores with a diameter of 7.4 µm or less were water-filled, possibly obstructing movement of P. graminis zoospores. By starting plants at –40 kPa for 10.5 days and then watering them to conducive matric potential, we found that WSBMV transmission occurred between 12 to 24 h at 15°C, and within 36 h at 20°C. No significant transmission occurred within 96 h at 6.5°C. In contrast, transmission of Wheat spindle streak mosaic virus (WSSMV) did not occur at 15°C (the only transmission temperature tested), suggesting either that WSSMV is unable to establish infection at 15°C or that a different vector is involved. The air pressure cell is a novel tool with many potential applications in research on the epidemiology and management of soilborne pathogens. Applications of the precise environmental control attained through the use of air pressure cells range from assessing the effects of cultural practices on soilborne inoculum to standardized virulence assays for soilborne pathogens to preliminary screens of host resistance and pesticide efficacy.

Perennial small grains offer the potential for sustainable production of forage and grain on marginal and erodable lands. The authors' results suggest that perennial small grains are at risk for infection by Soilborne wheat mosaic virus (SBWMV) and Wheat spindle streak mosaic virus (WSSMV) and that resistant cultivars may be needed for management of these diseases. Ideally, breeders should screen perennial small grain lines for resistance to soilborne viruses in the early stages of selection. Accepted for publication 27 October 2005. Published 30 November 2005.

The spatial pattern of Fusarium head blight (FHB) incidence was studied in 70 winter wheat fields in New York over a period of 3 years. Incidence of FHB was randomly distributed among 60 sampling areas in 64 of the 70 fields. Fields with random FHB ranged from 0.05 to 23% in average incidence of FHB and followed bean, cabbage, corn, oat, pea, sorghum, and soybean. There was strong evidence of aggregation in FHB only in three fields that had large concentrations of corn debris. Many fields had small, scattered fragments of corn debris in evidence from a corn crop two or more years prior to wheat. The lack of aggregation in FHB and low incidences of FHB in these fields suggests that weathered corn debris contributed relatively little within-field inoculum for FHB. Based on the predominantly random patterns of FHB, disease in rotational wheat fields of New York appears to be initiated primarily by deposition of spores from diffuse atmospheric populations of G. zeae. We hypothesize that these airborne spores may originate largely from inoculum sources external to wheat fields. Over-wintered corn residue, especially from the preceding crop season, on the soil surface is the most likely potential source of regional atmospheric inoculum for FHB in New York. Accepted for publication 10 March 2003. Published 18 April 2003.

To determine the potential contribution of seedborne Stagonospora nodorum to Septoria nodorum blotch epidemics, field plots that were isolated from other wheat plants or residues were sown to winter wheat with seed infection levels by S. nodorum of

In 1987-88 and 1988-89, field plot experiments were undertaken to assess the effects of wheat spindle streak mosaic virus (WSSMV), a soilborne virus transmitted by Polymyxa graminis, on winter wheat yields in New York. Two experimental approaches, reinfestation of fumigated plots with nonfumigated soil and a natural gradient of disease incidence, were used to produce different levels of disease. To minimize problems of covarying soil factors, yields of susceptible cultivars were compared with resistant cultivars in each experiment (...)

Triadimenol seed treatment was evaluated for control of early infections of spring wheat ( Triticum aestivum L. cultivars Max and Sinton) by Pyrenophora tritici-repentis (causal fungus of tan spot), Erysaphe graminis f. sp. tritici (causal fungus of powdery mildew), Leptosphaeria nodorum (causal fungus of Septoria nodorum spot), and Cochliobolus sativus (causal fungus of spot blotch). In controlled environment studies, triadimenol seed treatment controlled both tan spot and powdery mildew up to 20–30 days and 40–50 days after sowing, respectively. However, triadimenol seed treatment provided no control of early infection by airborne inoculum of L. nodorum and C. sativus . Powdery mildew-resistant cv. Max was completely free of symptoms or signs of E. graminis f. sp. tritici . In field experiments, triadimenol seed treatment controlled early development of tan spot and powdery mildew for 5 and 10 days longer, respectively, than in controlled environment studies. Control of both diseases in cv. Sinton and tan spot control in cv. Max resulted in yield increases of approximately 20% and 15%, respectively, at two different field locations.

(1986). Effect of temperature on tan spot development in spring wheat cultivars differing in resistance. Canadian Journal of Plant Pathology: Vol. 8, No. 4, pp. 451-454.

Four spring wheat (Triticum aestivum L.) cultivars exhibiting partial resistance to powdery mildew induced by Erysiphe graminis f.sp. tritici were crossed to a common susceptible cultivar to study the inheritance of resistance. The genetic parameters contributing to resistance were estimated by generation means analyses. Additive gene action was the most important genetic component of variation among generation means in all four crosses. Additive by additive effects were significant in one cross and both additive by additive and additive by dominance effects were significant in another. Dominance effects were not significant. The F2/F3 correlations in three crosses ranged from 0.27 to 0.43. Three additional crosses among resistant cultivars were employed to study the effectiveness of selection in improving resistance. By selecting the most resistant plants from the F2 and evaluating the progenies in the F4, increases in resistance ranging from 21% to 31% were obtained. In all crosses, there was transgressive segregation in both directions indicating that the genes conferring resistance to these cultivars differ and exhibit additive effects.