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Title:Soybean aphid intra-biotype variability based on colonization of specific soybean genotypes, resistance responses of soybean genotypes to pathogen infection after the application of chemical elicitors, and resistance to charcoal rot identified in ancestral soybean germplasm
Author(s):Pawlowski, Michelle
Advisor(s):Hartman, Glen L.
Department / Program:Crop Sciences
Discipline:Crop Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):ancestral soybean collection
charcoal rot resistance
salicylic acid
Sclerotinia stem rot
Phytophthora root and stem rot
charcoal rot
induced systemic resistance
systemic acquired resistance
aphid resistance
soybean aphid
Abstract:The soybean aphid, Aphis glycines Matsumura (Hemiptera; Aphididae), is one of the most destructive insect pests of soybeans (Glycine max) in the United States. One method for managing this pest is through host plant resistance. Since its arrival in 2000, four aphid biotypes have been identified that are able to overcome soybean aphid resistance (Rag) genes. A soybean aphid isolate collected from Moline, Illinois was not biotype 1 or biotype 2 because it readily colonized soybean plants with the soybean aphid resistance gene Rag2, unlike biotypes 1 and 2, but similar to soybean aphid biotype 3. Two no-choice experiments compared the virulence of the Moline isolate with biotype 3. In both experiments, differences in aphid population counts were not significant (P > 0.05) on soybean genotypes LD08-12957a (Rag2) and LD11-5413a (Rag2), but the aphid counts for the Moline isolate were significantly (P < 0.05) lower than the aphid counts for the biotype 3 isolate on the soybean genotypes Dowling (Rag1), LD05-16611 (Rag1), LD11-4576a (Rag1), and PI 567598B (rag1b and rag3). The Moline isolate was a variant of aphid biotype 3, which is the first report showing that soybean aphid isolates that classified as the same biotype, based on virulence against specific Rag genes, can differ in aggressiveness or ability to colonize specific host genotypes. Soybean is a major crop in the United States. Like all crops, soybeans are under constant threat of disease from invading pathogens and pests. One potential management method is to treat plants with elicitors to induce host resistance. The objective of this research was to determine if elicitors, previously shown to elicit defense responses in other host-pathogen interactions, could induce resistance in soybean. Two soybean genotypes producing high and low amounts of reactive oxygen species (ROS) after elicitation were selected for field experiments. In two consecutive growing seasons, five different elicitors and a water control were applied to foliage of both genotypes. Foliage and stems were evaluated for disease incidence and severity weekly and post-harvest. Overall, elicitors reduced disease severity in the soybean genotype with high ROS more than in the genotype with low ROS, and the specific reduction of a particular disease was associated with elicitor type in each year. In year 1, significant reductions occurred for anthracnose after treatment with benzothiadiazole; the same trend was found for charcoal rot after elicitation with phenylalanine and pod and stem blight after elicitation by chitosan in year 2 on the high ROS response genotype. In addition to the field studies, several greenhouse experiments were completed using additional soybean genotypes. Plants of genotype LD00-2817p survived at a higher rate after inoculation with Phytophthora sojae when treated with BTH, phenylalanine, and salicylic acid compared to a susceptible genotype. The current study showed the effectiveness of chemical elicitors and the potential to modify genotypes to effectively respond to elicitation to increase resistance to a broad spectrum of pathogens. Charcoal rot, caused by the fungal pathogen Macrophomina phaseolina, is a serious disease on soybean and other economic crops including corn, sorghum, and sunflowers. With few management options to control charcoal rot, more effort has focused on discovering new sources of host resistance. In this study, 70 ancestral accessions from the USDA Soybean Germplasm Collection were evaluated for charcoal rot resistance. Three experiments were used to evaluate soybean accessions; two lesion length experiments and a survival rate experiment. Results from these experiments indicated that three accessions, PI 548178, PI 548302, and PI 548414, showed significantly higher levels of partial resistance than the current moderately-resistant genotype, DT97-4290. The charcoal rot-resistant accessions found in this study will be useful to soybean breeders interested in breeding for charcoal rot resistance.
Issue Date:2015-04-27
Rights Information:Copyright 2015 Michelle Pawlowski
Date Available in IDEALS:2015-07-22
Date Deposited:May 2015

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