Genome-Wide Associations with Resistance to Bipolaris Leaf Spot (Bipolaris oryzae (Breda de Haan) Shoemaker) in a Northern Switchgrass Population (Panicum virgatum L.).

Switchgrass (Panicum virgatum L.), a northern native perennial grass, suffers from yield reduction from Bipolaris leaf spot caused by Bipolaris oryzae (Breda de Haan) Shoemaker. This study aimed to determine the resistant populations via multiple phenotyping approaches and identify potential resistance genes from genome-wide association studies (GWAS) in the switchgrass northern association panel. The disease resistance was evaluated from both natural (field evaluations in Ithaca, New York and Phillipsburg, Philadelphia) and artificial inoculations (detached leaf and leaf disk assays). The most resistant populations based on a combination of three phenotyping approaches-detached leaf, leaf disk, and mean from two locations-were 'SW788', 'SW806', 'SW802', 'SW793', 'SW781', 'SW797', 'SW798', 'SW803', 'SW795', 'SW805'. The GWAS from the association panel showed 27 significant SNPs on 12 chromosomes: 1K, 2K, 2N, 3K, 3N, 4N, 5K, 5N, 6N, 7K, 7N, and 9N. These markers accumulatively explained the phenotypic variance of the resistance ranging from 3.28 to 26.52%. Within linkage disequilibrium of 20 kb, these SNP markers linked with the potential resistance genes included the genes encoding for NBS-LRR, PPR, cell-wall related proteins, homeostatic proteins, anti-apoptotic proteins, and ABC transporter.

Trichothecene Genotype Composition of Fusarium graminearum Not Differentiated Among Isolates from Maize Stubble, Maize Ears, Wheat Spikes, and the Atmosphere in New York.

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.

Triazole Sensitivity in a Contemporary Population of Fusarium graminearum from New York Wheat and Competitiveness of a Tebuconazole-Resistant Isolate.

A sample of 50 isolates, including 25 each of the 3-acetyldeoxynivalenol and the 15-acetyldeoxynivalenol trichothecene genotype, from a contemporary collection of Fusarium graminearum associated with Fusarium head blight (FHB) of wheat in New York varied in sensitivity to tebuconazole (effective concentration leading to a 50% reduction of mycelial growth [EC50] of 0.28 to 8.09 mg/liter; µ = 1.12 mg/liter) and metconazole (0.05 to 0.86 mg/liter; µ = 0.33). Mean sensitivity did not differ between the trichothecene genotype groups. Isolate Gz448NY11 from Steuben County is the first tebuconazole-resistant field isolate of F. graminearum reported in the Americas and has the lowest sensitivity to tebuconazole (EC50 = 8.09 mg/liter) documented for this species. Suppression of FHB and deoxynivalenol (DON) following application of a commercial rate of tebuconazole was significantly diminished in plants inoculated with the tebuconazole-resistant isolate compared with those inoculated with a tebuconazole-sensitive isolate well documented for its aggressiveness and toxigenicity on wheat. There was no diminution of FHB and DON suppression with either isolate following application of metconazole. Significantly more individuals of the tebuconazole-resistant isolate were recovered from spikes inoculated with an equal mixture of the two isolates and sprayed with tebuconazole. Future studies are needed on the epidemiology and monitoring of triazole-resistant isolates to understand the risk that fungicide resistance poses to disease management and food security.

Fitness attributes of Fusarium graminearum isolates from wheat in New York possessing a 3-ADON or 15-ADON trichothecene genotype.

In all, 50 isolates of Fusarium graminearum from wheat spikes in New York, including 25 isolates each of the 15-acetyl-deoxynivalenol (15-ADON) and 3-ADON genotype, were tested to determine whether 3-ADON isolates are more fit for saprophytic survival and pathogenicity on wheat spikes than are 15-ADON isolates. The isolates were characterized and compared for 14 different attributes of saprophytic fitness and pathogenic fitness on a susceptible wheat variety. Isolates of the two genotypes could not be differentiated for most of these traits. Three principle components-ascospore production on corn stalks, total trichothecene amount in wheat kernels, and incidence of diseased spikelets up from the point of inoculation-accounted for 29.4, 18.9, and 10.8% of the variation among the isolates, respectively. A bootstrapping procedure grouped the isolates into two distinct groups, with 27 and 23 isolates each, with isolates from both genotypes represented in similar proportions (15-ADON/3-ADON, n = 14/13 and 11/12). Within the contemporary population of F. graminearum causing wheat head blight in New York, isolates with a 3-ADON genotype did not possess any detectable advantage over isolates with a 15-ADON genotype in saprophytic fitness or in pathogenic fitness on a susceptible wheat cultivar.

Greenhouse Evaluation of Seed and Drench Treatments for Organic Management of Soilborne Pathogens of Spinach.

The efficacy of 14 seed and drench treatments for control of soilborne damping-off pathogens in organic production of spinach was evaluated in a greenhouse study. The efficacy of each treatment was compared with nontreated seed and seed treated with a conventional fungicide for control of Fusarium oxysporum f. sp. spinaciae, Pythium ultimum, and Rhizoctonia solani. Two experimental seed treatments, GTG I and GTG II (each comprised of a proprietary organic disinfectant and the latter also containing Trichoderma harzianum T22), provided equivalent control to the conventional fungicide, mefenoxam, against P. ultimum in one trial and significant reduction of damping-off in the second trial. Natural II and Natural X (Streptomycete products), and Subtilex (Bacillus subtilis) seed treatments each suppressed damping-off significantly in one of the two trials. For R. solani, GTG I and Natural II seed treatments reduced damping-off as effectively as a drench with the fungicide Terraclor (pentachloronitrobenzene). A soil drench with Prestop (Gliocladium catenulatum) suppressed postemergence wilt caused by F. oxysporum in both trials; a compost tea drench and seed treatment with Yield Shield (Bacillus pumilis) each suppressed postemergence wilt in only one of two trials. GTG I and GTG II significantly increased seed germination compared to nontreated seed. No treatment was effective against all three pathogens, and some treatments exacerbated damping-off.