Soybean (Glycine max L. Merr.) is one of the most important crops of the world. Among the various viruses infecting soybean, peanut mottle virus is most commonly found on soybeans in areas where they are grown in close proximity to peanuts. This research was conducted with the primary objective of identifying new genes for resistance to peanut mottle virus. To assign a gene symbol to the resistance gene in cultivar CNS, it was crossed with 'Peking'. Both the F2 and F2:3 lines segregated in a ratio which is expected when one dominant and one recessive gene at two different loci are segregating. Previous studies indicate the presence of one dominant gene in CNS and one recessive gene in Peking for resistance against PMV. This clearly suggests that Peking and CNS possess different resistance genes, which are non-allelic to each other. Now that, all the allelism tests are complete, the resistance gene in CNS can be assigned a gene symbol of Rpv3. PI 486355, a resistant line, was crossed with susceptible cultivars Lee 68 and Essex to study the mode of inheritance of resistance. This PI was found to possess two independent dominant genes for resistance to peanut mottle virus. It was also crossed with 'York' and CNS which are known to have resistance genes at the Rpv1 and Rpv3 loci, respectively. Data from inoculations of F2 and F2:3 progenies indicated that one gene was allelic to Rpv1 and the other is at a locus different from both Rpv1 and Rpv3. PI 398593 was crossed with Lee 68, York, Peking and CNS for studying the nature of resistance genes present in it. No certain conclusions can be drawn regarding the nature of the resistance gene(s) at this stage because of inconsistent behavior of the PI itself. The F2 data of the crosses of PI 398593 with Lee 68, York and CNS supported a recessive nature of the resistance gene present in the PI. F2 plants of the cross PI 398593 x Peking segregated but, not in the expected ratio. F2:3 data of only one cross (PI 398593 x York) supported the recessive nature of the PI resistance gene whereas the other two crosses (PI 398593 x CNS and PI 398593 x Peking) did not support these findings. From the data available it appears that the resistance is at least partially influenced by the environment. The mode of inheritance of resistance in PI 96983, 'Kwanggyo', 'Toano', 'Jizuka', 'Raiden' and 'Suweon 97' was studied by crossing these cultivars with PMV susceptible cultivars and inoculating the F2 populations of these crosses. In all these cultivars resistance is governed by a single dominant gene. PI 96983, Toano, Jizuka and Suweon 97 were also crossed with York to determine the allelic relationships. Resistance genes in all these cultivars were found to be allelic to Rpv1. Since each of the cultivars also has a single dominant gene at the same locus for resistance to soybean mosaic virus, it is possible that resistance to both viruses is controlled by the same gene. / Master of Science

The possible existence of variability in the reaction of PMV in soybean, which could lead to resistance breaking strains, was investigated in this study. The specific research objectives were to provide evidence of PMV strains in soybean, and to characterize the PMV strains using aphid transmission efficiency and serological relationships. Twelve PMV isolates were placed in five strain groups (P1-P5) based on symptom expression in the soybean cultivars Lee 68, York, and Virginia. Aphid transmission efficiency of the PMV strains by the green peach aphid (Myzus persicae Sulz.) was determined by counting infected test plants following natural feeding by aphids exposed to virus infected source plants. Transmission efficiency from pea (Pisum sativum L.) source plants to pea test plants was 11 to 36% and varied with strains. Pea to soybean and soybean to soybean transmission was 5 to 29% and 20 to 58%, respectively. From these results, the 5 strains could be classified in 2 groups. Two techniques, SDS-immunodiffusion (sodium dodecyl sulfate) and ELISA (enzyme-linked immunosorbent assay), were used to investigate the serological relatedness of the PMV strains. Results indicated that all the strains were serologically closely related. / Ph. D.