Genetic Diversity for Resistance to Heterodera glycines Race 5 in Soybean.

Heterodera glycines is a serious pest of soybean in the United States. Plant introductions 90763 and 424595 are reported to be resistant to H. glycines race 5; however their genetic relationship for resistance is unknown. Crosses between these two lines and the susceptible cultivar Essex were studied in the F, F, and F generations to determine the number of genes involved in inheritance of resistance. The plants were screened using conventional techniques based on the index of parasitism. The data were subjected to analyses using chi-square test to determine goodness of fit between observed and expected genetic ratios. The cross PI 424595 x Essex segregated 1 resistant:63 susceptible in the F generation, which indicated the presence of three recessive genes controlling resistance to race 5. In the cross PI 90763 x Essex, resistance was conditioned by one dominant and two recessive genes. The cross between PI 424595 and PI 90763 segregated into 13 resistant:3 susceptible. The data fit a four-gene model with two recessive and two dominant genes with epistasis. PI 90763 has a dominant gene, whereas PI 424595 has a recessive gene; both share two additional recessive genes for resistance to race 5. This information is important to geneticists and soybean breeders for the development of cultivars resistant to H. glycines.