Resistance Genes in a 'Williams 82' x 'Hartwig' Soybean Cross to an Inbred Line of Heterodera glycines.

The number of resistance genes in soybean to soybean cyst nematode (SCN) Heterodera glycines was estimated using progeny from a cross of 'Williams 82' x 'Hartwig' (derived from 'Forrest'(3) x PI 437.654) screened with a fourth-generation inbred nematode line derived from a race 3 field population of SCN. Numbers of females developing on roots of inoculated seedlings were assigned to phenotype cells (resistant, susceptible, or segregating) using Ward's minimum variance cluster analysis. The ratio obtained from screening 220 F soybean families was not significantly different from a 1:8:7 (resistant:segregating:susceptible) ratio, suggesting a two-gene system for resistance. The ratio obtained from screening 183 F plants was not significantly different from a 3:13 (resistant:susceptible) ratio, indicating both a dominant (Rhg) and a recessive (rhg) resistance gene.