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 Benning 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.