Genetic mapping of antibiosis and antixenosis resistance mechanisms in soybean

Genetic maps were constructed using restriction fragment length polymorphism (RFLP) markers in F{dollar}sb2{dollar} populations of crosses between the insect-susceptible soybean (Glycine max (L.) Merr.) cultivar 'Cobb' and three insect-resistant plant introductions (PIs): PI171451; PI227687; and PI229358. Marker data were correlated with insect bioassay results from the same crosses to identify quantitative trait loci (QTLs) for insect resistance. Bioassays were designed to separate antibiosis and antixenosis mechanisms of soybean resistance to defoliating insects. The insect species used in the bioassays was the corn earworm, Helicoverpa zea (Boddie). Separate QTLs for antibiosis and antixenosis were detected.; A major QTL for both antibiosis and antixenosis was associated with the PI allele near marker A584V on linkage group (LG)'M' in the crosses Cobb {dollar}times{dollar} PI171451 and Cobb {dollar}times{dollar} PI229358. The same marker was tested in Cobb {dollar}times{dollar} PI227687 and was significantly associated with neither antibiosis nor antixenosis. Marker A584V on LG'M' was the only marker which was associated with both antibiosis and antixenosis.; Markers A083I on LG'F' and A343V-2 on LG'P' were associated with antibiosis QTLs in Cobb {dollar}times{dollar} PI227687. The QTL on LG'P' was conditioned by the PI227687 allele, while the QTL on LG'F' was associated with the Cobb allele at that locus. In Cobb {dollar}times{dollar} PI229358, antibiosis QTLs were found linked to marker L002H, on LG'G', and marker K401H, on LG'J'. The QTL on LG'G' was associated with the PI229358, whereas the resistance allele on LG'J' was provided by Cobb.; A minor antixenosis QTL was associated with the resistant parent allele of marker R249T on LG'H' in all three crosses. Minor antixenosis QTLs were associated with the resistant parent alleles at A132T on LG'C2' and Bng047D on LG'D1' in Cobb {dollar}times{dollar} PI227687 and Cobb {dollar}times{dollar} PI229358, respectively. An antixenosis QTL was associated with the Cobb allele of marker B212V-1 on LG'F' in Cobb {dollar}times{dollar} PI171451. This marker has been previously associated with QTLs for resistance to a variety of soybean pathogens (Tamulonis et al. 1997b). Marker B212V-1 was monomorphic in Cobb {dollar}times{dollar} PI227687 and Cobb {dollar}times{dollar} PI229358 and it is possible that PI227687 and PI229358 both also possess this resistance allele. The antibiosis QTL on LG'F' detected in Cobb {dollar}times{dollar} PI227687 was not linked to the antixenosis QTL found on LG'F' in Cobb {dollar}times{dollar} PI171451.