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

Post anthesis drought stress is a common problem in winter wheat (Triticum aestivum L.) production throughout the west central and southern Great Plains of the USA. Contact chemical desiccants have been proposed to simulate postanthesis drought stress in the field and to enable selection for postanthesis drought stress tolerance. This study was conducted to determine if early generation among cross selection for chemical desiccation tolerance is possible and if chemical desiccation tolerance of early generation bulks could be altered using mechanical mass selection for kernel weight. The chemical desiccation tolerance of four winter wheat single cross populations was evaluated in 1991 at two locations in Colorado, each location consisting of replicated F-4-bulk trials of populations that had been subjected to chemical desiccation [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 both locations, a cross between tolerant parents showed lower (P less than or equal to 0.01) chemical desiccation injury (for grain yield, kernel weight, and test weight) than crosses between sensitive parents or between contrasting parents. Separation of F-2 populations into selected 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 similar anthesis dates. Mechanical mass selection within populations advanced with two cycles of chemical desiccation produced F-4-bulk populations with significantly (P less than or equal to 0.01) lower chemical desiccation injury. The potential for selective improvement of chemical desiccation tolerance of bulk populations was indicated by several instances of reduced chemical desiccation injury for populations advanced to the F-4 with desiccant application and mechanical mass selection for high kernel weight. Our results provide evidence that crosses tolerant of chemical desiccation can be identified using early generation evaluation of bulk-populations, prior to extensive line extraction and evaluation.