Screening Soybean Genotypes in the Greenhouse for Resistance to Insects

Insect resistance in soybean, Glycine max (L.) Merr., cultivars would reduce the use of chemical insecticides, resulting in less risk to the environment and increased grower profits. The objectives of this research were to develop an effective greenhouse screening procedure to identify soybean genotypes with resistance to defoliating insects and provide information on the number of replications required to obtain desired levels of precision for the procedure. Neonate larvae were placed on 12- to 16-d-old potted plants. Insects had free choice among plants for 14 d within replicates, but larval movement away from a replicate was prevented by maintaining the potted plants in stainless steel pans containing 2 cm of water. Replicate blocks were separated so that leaves did not intermingle. Several hundred soybean genotypes were evaluated at one time. Defoliation of test plants by the corn earworm, Heliothis zea (Boddie), in the greenhouse screening system correlated (r = 0.60; P < 0.01) insect defoliation of soybean plants in field nurseries. The ranking of the genotypes based on defoliation by the corn earworm; tobacco budworm, H. virescens (Fabricius); soybean looper, Pseudoplusia includens (Walker); velvetbean caterpillar, Anticarsia gemmatalis Hübner; green cloverworm, Plathypena scabra (Fabricius); beet armyworm, Spodoptera exigua (Hübner); and fall armyworm, S. frugiperda (J.E. Smith), was similar in greenhouse tests. For example, feeding by all insect species was inhibited by Plant Introduction 229358 and GatIRSI-296, genotypes with known multiple insect resistance. Of seven insect species tested, the corn earworm was the easiest to work with in the greenhouse screening program and required fewer replications than most other species to demonstrate stipulated levels of resistance. For example, a difference of 40% in the overall mean of the experiment between two genotypes required seven replicates with corn earworm and 18 replicates with soybean looper. The greenhouse procedure has been used successfully for 3 yr and is a good complement to field testing in a soybean pest resistance program. This research was supported by state and Hatch funds from the Georgia Agric. Exp. Stns. and grants from the Georgia Agricultural Commodity Commission for Soybeans.