Laboratory testing and molecular analysis of the resistance of wild and cultivated soybeans to cotton bollworm, Helicoverpa armigera (Hübner)

Abstract

Identifying a superior soybean variety with high defoliator resistance is important to avoid yield loss. Cotton bollworm (Helicoverpa armigera Hübner) is one of the major defoliators of soybean (Glycine max [L.] Merr.) worldwide. In this study, we evaluated the effect of H. armigera larvae on ED059, a wild soybean (Glycine soja Sieb. et Zucc.), and three cultivated soybean varieties: Tianlong 2, PI 535807, and PI 533604, in choice and no-choice assays. The percentage of ED059 leaflets consumed by H. armigera was lower than that of the three cultivated soybeans. Larvae that fed on ED059 exhibited low weight gain and high mortality rate. Waldbauer nutritional indices suggested that ED059 reduced the growth, consumption, and frass production of H. armigera larvae. Larvae that fed on ED059 showed lower efficiency of conversion of ingested and of digested food than those that fed on Tianlong 2 and PI 533604. However, they showed statistically similar consumption index and approximate digestibility compared with those fed on the three cultivated soybeans. Quantitative real-time PCR analysis revealed that 24h after insect attack, ED059 had higher transcript levels of Kunitz trypsin inhibitor 3, Cysteine proteinase inhibitor 2, and Nerolidol synthase 1 but a lower transcript level of Pathogenesis-related protein 1 than Tianlong 2. The gene expression results were consistent with the presence of higher levels of jasmonic acid (JA) and transcript levels of the JA biosynthesis enzyme allene oxide cyclase 3 in ED059 than in Tianlong 2. Our findings indicate that ED059 is a superior soybean line with strong insect resistance that may be mediated via the JA pathway.