HETEROSIS AMONG INSECT-RESISTANT MAIZE POPULATIONS

Information on heterosis is critical to assimilation of desirable trai ts into usable maize, Zea mays L., germplasm. Our objective was to ide ntify maize populations with heterosis for desirable traits. Twelve so uthern-adapted maize populations with resistance to damage by ear and leaf-feeding insects and all 66 possible population crosses were evalu ated in a randomized complete-block design in three environments. Popu lation effects, heterosis, and specific combining ability (SCA) effect s were estimated for seven plant traits. Population effects were signi ficant (P less-than-or-equal-to 0.01) for all traits except yield, het erosis effects were significant for all traits, and SCA effects were s ignificant for all traits except insect damage. Population and average heterosis effects were less important among genetic effects than SCA, which accounted for more than one-half the heterosis sums of squares for all traits. Population performance as a predictor of relative cros sbred performance was least effective for grain yield and quality. Ave rage heterosis, relative to midparent values, varied from 2.2% for lod ging to 22.5% for yield. Crosses existed with SCA effects for resistan ce to one or more insects for all traits. Genotype x environment inter actions were significant for all traits except insect damage. Heterosi s interactions with environment accounted for more variation than popu lation x environment interactions. Among heterosis interactions with e nvironments, those due to average heterosis and SCA effects were of gr eatest significance. The information will be useful in the development of germplasm with resistance to insects and improved agronomic perfor mance.