Genetic Analyses of Soybean Genotypes Resistant to Soybean Cyst Nematode Race 5
- S. C. Anand and
- A. P. Rao-Arelli
All soybean [Glycine max (L.) Merr.] cultivars currently grown in the USA are susceptible to soybean cyst nematode (SCN), Heterodera glycines Ichinohe, Race 5. Soybean plant introductions (PIs) with resistance to SCN Race 5 have been identified, but there is very little information on their genetic analyses for resistance. Our objectives were to determine inheritance of resistance in three PIs for reaction to SCN Race 5, and to evaluate five resistant PIs for their genetic relationship to SCN resistance. The F2 plants and F3 families from nine different crosses among resistant (R) and susceptible (S) genotypes were evaluated in the greenhouse. Each seedling was inoculated with about 1000 eggs and juveniles of SCN Race 5. Plant roots were washed after 30 d and white females enumerated. Based on the index of parasitism (IP) F2 plants and F3 progenies were categorized as resistant, susceptible, or segregating. The chisquare test was applied to determine goodness of fit between observed and expected genetic ratios. The segregation data from crosses ‘Peking’ (R) ✕ PI 88788(S), PI 438489B(R) ✕ PI 88788(S), and PI 90763(R) ✕ ‘Forrest’(S) indicated that resistance in Peking and PI 90763 was conditioned by two recessive genes each, whereas PI 438489B had one recessive gene. Crosses between resistant parents, Peking with PI 90763, PI 404166, and PI 84751 have segregated for resistance indicating that genes in Peking compared to other parents are located at different loci. Lack of segregation in crosses of PI 90763(R) ✕ PI 404166(R), Peking(R) ✕ PI 438489B(R) and PI 90763(R) ✕ PI 438489B(R) indicated that the resistance in these parents was controlled by alleles at the same locus. These results showed that there was at least one gene for resistance different in Peking, PI 90763, and PI 404166. Intercrossing these sources of different genes for resistance to SCN Race 5 should result in germplasm with potentially higher levels of resistance. This information will assist breeders in selecting resistant sources to SCN Race 5 for cultivar development.
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