Fine mapping of a major insect resistance QTL in soybean and its interaction with minor resistance QTLs

Utilization of native insect resistance genes can be an important component for managing insects in soybean [Glycine max (L.) Merr.]. A major quantitative trait locus (QTL-M) for insect resistance from PI 229358, controlling antibiosis and antixenosis, was previously identified on linkage group (LG) M and was found to increase the effectiveness of a Bacillus thuringiensis (Bt) transgene in soybean. The objectives of this study were to fine-map QTL-M using recombinant substitution lines (RSLs) identified from a 'Benning' backcross population, and to evaluate the main effects and the epistatic interactions between QTL-M and other resistance QTLs on LGs G and H using near-isogenic lines (NILs) in a Benning genetic background. The effect of QTL-M was still detectable in the Benning NILs when they were evaluated for resistance to corn earworm [CEW, Helicoverpa zea (Boddie)]. The two minor resistance QTLs only provided insect resistance when QTL-M was also present in the Henning NILs. The QTL-M was fine-mapped to an approximately 0.52-cM region after the first round of phenotyping the RSLs for resistance to CEW and soybean looper [SBL, Pseudoplusia includens (Walker)]. These results should increase the feasibility of cloning QTL-M and help guide the development of insect resistant soybean cultivars.