RFLP mapping and marker-assisted selection of soybean cyst nematode resistance in PI 209332

Soybean cyst nematode (Heterodera glycines Ichinohe; SCN) is one of the most serious disease problems of soybean [Glycine max (L.) Merrill], but the genetic basis of SCN resistance is complex and poorly understood. This study was conducted to identify genomic regions that confer partial resistance to SCN in soybean PI 209332 through the use of DNA genetic markers. By testing three different races of SCN, we also assessed race-specificities of putative resistance loci. Mapping was performed in two related populations, one an F_2.3 population and the other an F_5:6 recombinant inbred line population, both derived from a single cross between 'Evans' and PI 209322. To identify resistance loci, SCN disease responses for all lines in the mapping populations were contrasted with DNA marker genotypes at 98 restriction fragment length polymorphism (RFLP) marker loci spread throughout the soybean genome. A major partial-resistance locus on linkage group 'G' (P < 0.0001) near RFLP marker C006V was effective against all three SCN race isolates tested. This locus explained 35% of total phenotypic variation in the SCN disease response to a Race 1 SCN population, 50% of the response to a Race 3 SCN population, and 54% of the response to a Race 6 SCN population. Additional putative SCN resistance loci (P < 0.002) were identified on soybean linkage groups 'D', 'J', 'L', and 'K'. Detecting some of these minor loci was complicated by strong masking phenotypic effects of the major resistance locus near C006V. Some of the putative resistance loci behaved in a race-specific manner. Based on RFLP genotype at the F₂ generation, marker-assisted selection for the resistance locus on linkage group 'G' was evaluated and found to be 90% accurate in selecting F_5:4 lines resistant to SCN, comparable in accuracy to phenotypic selection for SCN resistance.