Quantitative trait loci for antixenosis resistance to corn earworm in soybean

Insect resistance in soybean, Glycine mnu (L.) Merr., is inherited quantita tively and has been difficult to incorporate into high-yielding cultivars. The objectives of this study were to: (i) use restriction fragment length p olymorphism (RFLP) markers to identify quantitative trait loci (QTLs) for a ntixenosis (nonpreference) resistance to corn earworm, Helicoverpa tea Bodd ie, in soybean plant introductions PI171451 and PI227687, (ii) determine th e location of the QTLs on the public soybean genetic linkage map, (iii) det ermine their relative magnitude and gene action, and (iv) compare them to i nsect resistance QTLs previously detected in PI229358. RFLP maps were const ructed in two insect-susceptible x insect resistant soybean populations: Co bb x PI171451 and Cobb x PI227687. Insect resistance was measured either in the field or greenhouse as percentage defoliation by corn earworm on veget ative soybean plants. Marker-QTL associations were detected by interval map ping and confirmed by single-factor analysis of variance. Comparisons were made between QTLs identified in this study and those identified previously using PI229358 as the source of insect-resistant germplasm. Among the three resistant genotypes (PI171451, PI227687, and PI229358) a QTL on linkage gr oup (LG) 'H' was shared among all three genotypes (accounting for an R-2 Of 19, 9, and 17%, respectively), and a major QTL on LG 'M' was shared betwee n PI171451 and PI229358 (R-2 = 37% for each). A minor QTL on LG 'C2' was id entified which was unique to PI227687 (R-2 = 11%) and a minor QTL on LG 'D1 ' was identified which was unique to PI229358 (R-2 = 12%) In addition, a QT L was found on LG 'F' in the susceptible genotype, Cobb (R-2 = 20%). This Q TL is in a region of the soybean genome which has been previously associate d with a cluster of soybean pathogen-resistance loci.