Quantitative trait loci with additive and epistatic effects underlying resistance to two HG types of soybean cyst nematode.

The resistance of soybean ( Glycine max L. Merr.) cultivars varies with the different races of the soybean cyst nematode ( SCN), Heterodera glycines, referred to as HG types (biotypes). Resistant cultivars with durable resistance are emphasized in recent years. The aim here was to identify quantitative trait loci ( QTLs) for resistance to two SCN HG types ( HG type 2.5.7, race 1; and HG type 1.2.3.5.7, race 4) in resistant cultivar 'L-10' and to analyse the additive and epistatic effects of the identified QTLs. A total of 140 F5-derived F10 recombinant inbred lines (F5:10 RILs) were advanced via single-seed-descent from the cross between 'L-10' (broadly resistant to SCN) and 'Heinong 37' ( SCN-susceptible). For SCN HG type 2.5.7 and HG type 1.2.3.5.7 resistance, three and six QTLs for resistance to SCN HG type 2.5.7 and HG type 1.2.3.5.7 were identified, respectively, most of which could explain <10% of the phenotypic variation. Among these QTLs, five were identified over 2 years, while the other QTLs were detected in either 2009 or 2010. QSCN1-2, located near the SSR marker Sat_069 of linkage group D1b (Chromosome, 2), was responsible for the largest proportion of phenotypic variation (16.01% in 2009 and 18.94% in 2010), suggested that it could effectively be used as a candidate QTL for the marker-assisted selection ( MAS) of soybean lines resistant to SCN. Additionally, for SCN HG type 2.5.7 and HG type 1.2.3.5.7 resistance, two and four QTLs showed an additive effect ( a), respectively. One epistatic pair of QTLs ( QSCN1-1- QSCN1-3) for SCN HG type 2.5.7 resistance and eight epistatic pairs of QTLs for SCN HG type 1.2.3.5.7 resistance were found to have significant aa effects, among which one pair of QTLs ( QSCN4-4 and QSCN4-5) contributed a large proportion of aa effects (3%). The results indicated that additive and epistatic effects could significantly affect SCN resistance. Therefore, both of a and aa effects should be considered in MAS programmes. [ABSTRACT FROM AUTHOR]