DIVERGENT SELECTION FOR GROWTH IN JAPANESE-QUAIL UNDER SPLIT AND COMPLETE NUTRITIONAL ENVIRONMENTS .7. HETEROSIS AND COMBINING ABILITY AMONG DIALLEL CROSSES FOLLOWING 27 GENERATIONS OF SELECTION

Growth patterns of quail lines divergently selected for 4-wk BW under split and complete nutrition environments were investigated utilizing a diallel mating scheme. The design, involving 16 mating combinations, allowed investigation of heterotic effects, reciprocal cross effects, and combining ability. Progeny from Generation 27 breeders were evalu ated in two hatches under both selection diets. Heterosis for hatch we ight was essentially zero; however, percentage heterosis from High x H igh crosses and Low x Low crosses ranged from 5 to 18% after 1 wk of a ge. Quail progeny from Low x High crosses were consistently larger tha n quail from reciprocal High x Low crosses under both selection diets. Reciprocal differences were greatest immediately posthatch and declin ed with age. However, in crosses involving males from High and Low spl it diet lines mated to females from High and Low complete diet lines, large reciprocal differences in BW remained at 8 wk. Mean heterosis va lues for BW across ages from crossing High and Low lines both within a nd across selection environments were negative in six of eight compari sons. Mean values ranged from +3 to -11% and indicated that greater se lection responses may have been made in divergent selection for low 4- wk BW than for high BW. General combining ability of lines was greater when transmitted via females as opposed to males, and was similar und er the two diets (split and complete). There was evidence that high-BW lines exhibited greater general combining ability under both dietary environments than did low-BW lines.