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 (SC N) Heterodera, glycines was estimated using progeny from a cross of 'W illiams 82' x 'Hartwig' (derived from 'Forrest'(3) x PI 437.654) scree ned with a fourth-generation inbred nematode line derived from a race 3 field population of SCN. Numbers of females developing on roots of i noculated seedlings were assigned to phenotype cells (resistant, susce ptible, or segregating) using ard's minimum variance cluster analysis. The ratio obtained from screening 220 F-3 soybean families was not si gnificantly different from a 1:8:7 (resistant:segregating:susceptible) ratio, suggesting a two-gene system for resistance. The ratio obtaine d from screening 183 F-2 plants was not significantly different from a 3:13 (resistant:susceptible) ratio, indicating both a dominant (Rhg) and a recessive (rhg) resistance gene.