EARLY-GENERATION SELECTION FOR CHEMICAL DESICCATION TOLERANCE IN WINTER-WHEAT

Post anthesis drought stress is a common problem in winter wheat (Trit icum aestivum L.) production throughout the west central and southern Great Plains of the USA. Contact chemical desiccants have been propose d to simulate postanthesis drought stress in the field and to enable s election for postanthesis drought stress tolerance. This study was con ducted to determine if early generation among cross selection for chem ical desiccation tolerance is possible and if chemical desiccation tol erance of early generation bulks could be altered using mechanical mas s selection for kernel weight. The chemical desiccation tolerance of f our winter wheat single cross populations was evaluated in 1991 at two locations in Colorado, each location consisting of replicated F-4-bul k trials of populations that had been subjected to chemical desiccatio n [2% (w/v) NaClO3 applied 10 d postanthesis] and divergent mechanical mass selection for kernel weight in the F-2 and F-3 generations. At b oth locations, a cross between tolerant parents showed lower (P less t han or equal to 0.01) chemical desiccation injury (for grain yield, ke rnel weight, and test weight) than crosses between sensitive parents o r between contrasting parents. Separation of F-2 populations into sele cted bulks of differing height and maturity showed that selected-bulks from randomly selected and tall F-2 plants suffered significantly (P less than or equal to 0.01) lower chemical desiccation injury (at one location only) than selected bulks from short plants or plants with si milar anthesis dates. Mechanical mass selection within populations adv anced with two cycles of chemical desiccation produced F-4-bulk popula tions with significantly (P less than or equal to 0.01) lower chemical desiccation injury. The potential for selective improvement of chemic al desiccation tolerance of bulk populations was indicated by several instances of reduced chemical desiccation injury for populations advan ced to the F-4 with desiccant application and mechanical mass selectio n for high kernel weight. Our results provide evidence that crosses to lerant of chemical desiccation can be identified using early generatio n evaluation of bulk-populations, prior to extensive line extraction a nd evaluation.