The number of resistance genes in PI 89772 and PI 209332 conferring resistance to H. glycines race 3 is not well defined. Crosses of PI 89772 × 'Lee 68', PI 88788 × PI 89772, and 'Lee 68' × PI 209332 were made in the field and greenhouse. Several F1 and F[sub2] families from each cross, 98 F[sub3] families from cross PI 89772 × 'Lee 68', 74 F[sub3] families from cross PI 88788 × PI 89772, and 80 F[sub3] families from cross 'Lee 68'× PI 209332 were tested with an inbred line of H. glycines developed on PI 88788 to determine the level and inheritance of resistance. Approximately 8,000 individual plants growing in pots containing 200 cm3 of sterilized sand were inoculated with 4,000 eggs and J2/pot. Thirty days after inoculation the number of females that developed on each plant was determined. Cluster analysis revealed sets of families with a low mean number of females and low variance, intermediate means and high variance, and high means with a low variance, indicating F[sub3] plants came from, respectively, homozygous resistant, heterozygous or segregating, and homozygous susceptible F[sub2] plants. Thus, resistance classes were considered as quantitative parameters having different levels of resistance as opposed to only two classes, either resistant or susceptible. Chi-square analysis of segregation of phenotypic data indicated two genes confer resistance to race 3 of H. glycines. The three H. glycinesresistant parents have at least two genes that express resistance to H. glycines. One gene acts as a major gene (Rhg[subx]) and the other a minor gene (Rhg[suby]) in conferring resistance of the parents PI 89772 (Rhg[subx][sub2][sub?] Rhg[subx][sub2][sub?] Rhg[suby][sub1][sub?]Rhg[suby][sub1][sub?]), PI 88788 (Rhg[subx][sub2][sub?] Rhg[subx][sub2][sub?] Rhg[suby][sub2][sub?] Rhg[suby][sub2][sub?]), and PI 209332 (Rhg[subx]3? Rhg[subx]3? Rhg[suby]3? Rhg[suby]3?) to H. glycines race 3. The same genes may occur in PI 209332 as in PI 89772, but support for this hypothesis must be obtained by studying the cross PI 209332 × PI 89772. The same major (Rhg[subx]) and minor (Rhg[suby]) genes occur in PI 89772 (Rhg[subx][sub2][sub?] Rhg[subx][sub2][sub?] Rhg[suby][sub1][sub?] Rhg[suby][sub1][sub?]) and PI 88788 (Rhg[subx][sub2][sub?]Rhg[subx][sub2][sub?]Rhg[suby][sub2][sub?]Rhg[suby][sub2][sub?]). The phenotypic ratios obtained in this research indicate that epistasis occurs between gene Rhg[subx] and gene Rhg[suby]. Results from this analysis indicated that the sensitivity of resistant genotypes to the environment is different from that of susceptible genotypes. In addition, a maternal effect was found for the inheritance of resistance of PI 88788 to H. glycines race 3, but not for PI 89772.
