Description

Abstract: Advanced breeding lines of soybean (GLycine max (L.) Merr.) were evaluated for resistance to leaf-feeding by corn earworm (CEW) (Heliothis zea (Boddie)) using three screening techniques. The conservative method of testing larval growth on intact leaves was compared with two techniques commonly used for preliminary screening of CEW resistance- measurement of larval growth on excised leaves and field evaluation of CEW leaffeeding damage to small plots. The parental lines ‘Forrest,’ ‘Bragg,’ and the CEW-resistant plant Introduction PI229358 served as checks for the experiments. Mean weights of 14-d-old larvae reared on intact leaves of greenhouse-grown plants were positively correlated with the weights of 14-d-old larvae reared on excised leaves taken from the same plants. Mean weights of larvae fed the intact leaves, however, differentiated resistance better than weights of larvae fed the excised leaves. Mean weights of larvae (14 d old) reared on intact leaves were positively correlated with mean leaf damage by CEW to naturally infested one- and three-row plots in 1980 and 1983 field tests. Although ratings of resistance were similar for test of larval growth on intact leaves and evaluation of leaf damage by CEW in small field plots, we recommend repeated testing or combined use of both methods to distinguish highly resistant lines from lines with intermediate levels of resistance.