| Sudden death syndrome (SDS) caused by the soilborne fungus Fusarium solani f. sp. glycines (FSG) is a major disease in soybean [Glycine max (L.) Merr.]. The objective of my first study was to evaluate the effect of field inoculation methods, soil compaction, and irrigation timing on the occurrence of SDS symptoms. Six FSG inoculation methods were evaluated during two years. Three experiments were also conducted to evaluate the effect of compaction and irrigation on SDS symptom occurrence. The inoculation methods that produced the most severe foliar symptom included placing infested sorghum below the seed prior to planting and planting infested popcorn in the furrow with the soybean seed. No significant effects of soil compaction on SDS foliar symptom development were observed. The irrigation treatments during mid to late reproductive growth stages resulted in the greatest increases in SDS foliar symptom development.; The objective of the second study was to evaluate two SDS greenhouse screening methods and determine which best correlates with field resistance of soybean genotypes. Three sets of genotypes were evaluated with the greenhouse cone method and with the greenhouse tray method. The correlations between the SDS ratings of genotypes in the field and in the greenhouse with cones ranged from 0.58 (p<0.001) to 0.69 (p<0.001) and between field and greenhouse tray ratings was 0.54 (p<0.001) for Set 1 and 0.39ns for Set 2. The cone method has successfully predicted field results for all three sets evaluated, and can be used for predicting field SDS resistance reactions of genotypes.; The objective of my third study was to detect QTL conferring SDS resistance in two populations of recombinant inbred lines (RILs) populations. These populations were from the crosses PI 567374 x 'Omaha' and 'Ina' x LN91-1695. Six chromosomal regions were significantly associated with SDS resistance in the PI 567374 x Omaha population. For all regions, the beneficial alleles were derived from PI 567374. Five chromosomal regions were associated with SDS resistance in the Ina x LN91-1695 population. Two regions previously found to be associated with SDS resistance in the cultivar Essex derived the resistance from the resistant parent Ina. |
