Cross to an Inbred Line of Heterodera glycines 1

T h e n u m b e r o f resistance genes in soybean to soybean cyst nematode (SCN) Heterodera glycines was est imated using progeny f rom a cross of 'Williams 82' x 'Hartwig' (derived f rom 'Forrest '~ x PI 437.654) screened with a four th-genera t ion inbred nematode line der ived f rom a race 3 field popula t ion o f SCN. Numbers o f females developing on roots o f inoculated seedlings were assigned to pheno type cells (resistant, susceptible, or segregating) using Ward 's min imum variance cluster analysis. T h e ratio obtained f rom screening 220 F s soybean families was not significantly d i f fe rent f rom a 1:8:7 (resistant:segregating:susceptible) ratio, suggesting a two-gene system for resistance. T h e ratio obtained f rom screening 183 F 2 plants was not significantly d i f fe ren t f rom a 3:13 (resistant:susceptible) ratio, indicating both a dominan t (Rhg) and a recessive (rhg) resistance gene.