WHEAT BREEDING NURSERIES, TARGET ENVIRONMENTS, AND INDIRECT SELECTIONFOR GRAIN-YIELD

Use of appropriate nursery environments will maximize gain from select ion for yield of wheat (Triticum aestivum L.) in the target population of environments of a breeding program. The objective of this study wa s to investigate how well-irrigated (low-stress) nursery environments predict yield of lines in target environments that varied in degree of water limitation, Fifteen lines were sampled from the preliminary yie ld evaluation stage of the Queensland wheat breeding program and teste d in 26 trials under on-farm conditions (Target Environments) across n ine years (1985 to 1993) and also in 27 trials conducted at three rese arch stations (Nursery Environments) in three years (1987 to 1989). Th e nursery environments were structured to impose different levels of w ater and nitrogen (N) limitation, whereas the target environments repr esented a random sample of on-farm conditions from the target populati on of environments, Indirect selection and pattern analysis methods we re used to investigate selection for yield in the nursery environments and gain from selection in the target environments, Yield under low-s tress nursery conditions was an effective predictor of yield under sim ilar low-stress target environments (r = 0.89, P < 0.01). However, the value of the low-stress nursery as a predictor of yield in the water- limited target environments decreased with increasing water stress (mo derate stress r = 0.53, P < 0.05, to r = 0.38, P > 0.05; severe stress r = -0.08, P > 0.05), Yield in the stress nurseries was a poor predic tor of yield in the target environments, Until there is a clear unders tanding of the physiological-genetic basis of variation for adaptation of wheat to the water-limited environments in Queensland, yield impro vement can best be achieved by selection for a combination of yield po tential in an irrigated low-stress nursery and yield in on-farm trials that sample the range of water-limited environments of the target pop ulation of environments.