Evaluating genetic diversity for heat tolerance traits in Mexican wheat landraces

Large areas of wheat (Triticum aestivum L. Fion et Paol.) are grown under a bove-optimal temperatures causing significant yield reductions. Adaptation of wheat to such areas through genetic improvement is a way of increasing p roduction in those regions. To identify new and novel sources of heat toler ance, 2,255 Mexican wheat landraces, grown for seed regeneration under semi -controlled conditions in the screenhouse, were evaluated for leaf chloroph yll content (LCC). The landraces were collected from areas with seasonal hi gh temperatures. Based on these initial results, two subgroups of 127 landr aces each were selected, one with high LCC values and one with low LCC valu es. During 1997 the selected subgroups were grown in the screenhouse and in field trials in Cd. Obregon, Mexico. The landraces were evaluated for trai ts associated with heat tolerance: LCC, canopy temperature depression, and thousand-kernel weight (KWT). The objectives of the study were to identify new sources of heat tolerance and to assess the feasibility of combining ba sic seed regeneration with characterization for needed traits like heat tol erance. A highly significant correlation was found between LCC in the scree nhouse and in field trials, indicating the promise of using a screenhouse f or cost effective evaluation of heat tolerance traits. This strategy could be used to identify regions or groups of germplasm that merit more intense screening. Highly significant correlations were also found between LCC and KWT. Three landrace cultivars with superior and consistent LCC values were identified. These accessions are potentially useful sources for improving h eat tolerance in cultivated wheat.