Effect of Pubescence Tip on Soybean Resistance to Lepidopteran Insects

DNA marker analysis has mapped a quantitative trait locus for soybean, Glycine max (L.) Merr., resistance to the corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), on the USDA soybean genetic linkage map near the classical gene Pb, which conditions pubescence tip. This study was initiated to determine the effect of pubescence tip on resistance to H. zea larvae and to examine the effect on beet armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), and soybean looper, Pseudoplusia includens (Walker) (Lepidoptera: Noctuidae), larvae. The effect of blunt (pb) and sharp (Pb) pubescence tip was tested in antixenosis and antibiosis bioassays on H. zea, S. exigua, and P. includens larvae with near-isolines and insect-resistant and -susceptible genotypes differing in pubescence tip morphology. Sharp pubescence tip significantly reduced defoliation (antixenosis) from H. zea, S. exigua, and P. includens and weight gain (antibiosis) of H. zea. The weight gain of P. includens was unaffected, and S. exigua weight gain was significant for one pair of near-isolines differing in pubescence tip but not the other. The results indicate that sharp pubescence tip would be beneficial to introgress into elite soybean germplasm due to its association with resistance to H. zea, S. exigua, and P. includens.