POSTANTHESIS TEMPERATURE EFFECTS ON DURATION AND RATE OF GRAIN FILLING IN SOME WINTER AND SPRING WHEATS

To help define traits that are likely to improve wheat (Triticum aestivum L.) grain yield in a warm, humid continental climate, genotypic variations in various grain growth characteristics in wheat were examined. Winter habit cultivars were grown indoors under a 16-h photoperiod and at day/night temperatures of 20/15-degrees-C, and spring habit cultivars at temperatures ranging from 15/15-degrees-C to 30/25-degrees-C. Grain-filling duration of the winter wheats varied from 36.4 d for Peking-10 to 31.8 d for Priboy. Final kernel weights, which varied from 61.7 mg for Lovrin-10 to 38.3 for Jokionen-3057, were highly correlated with rates of dry matter accumulation. Grain-filling duration of the spring wheats ranged from 56.4 to 47.0 d at 15/15-degrees-C, and from 23.8 to 18.1 d at 30/25-degrees-C. Grain number per spike decreased from 15/15-degrees-C to 30/25-degrees-C. The inverse of grain-filling duration was linearly related to mean temperature, with the intercept on the x-axis (the base temperature of grain filling) being the same for all cultivars. Variation for grain-filling duration among the genotypes tested was present, although small in relation to temperature effects. Breeding for extended grain-filling duration as a strategy for increasing wheat grain yield in a warm climate will thus be difficult. However, an application of the degree-day concept would be desirable.