Rate and Duration of Grain Fill in Spring Wheat1

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Abstract
The grain fill (GF) period of spring wheat (Triticum aestivum L.) grown in the Northern Great Plains coincides with periods of drought and high temperature stress, whicho ften reduce crop yield and quality. Rate and duration of GF were determined for 20 spring wheat genotypes in four rainfed North Dakota environments to evaluate genotypic variation for rate and duration of GF, and to examine relationships between estimated GF parameters, environmental limitations, wheat productivity, and stress tolerance in environments prone to postanthesis drought and high temperature stresses. A quadratic polynomial was used to describe the relationship between kernel weight and accumulated growing‐degree days from anthesis to maturity. Rate and duration of GF were estimated from fitted curves. Genotypes varied for both GF rate and duration, but increasing temperatures during GF tended to stop grain growth prematurely and to hasten physiological maturity. Rate, but not duration of GF, was correlated with kernel weight. Increasing kernel weight by extension of the GF period does not appear to be a promising strategy for increasing grain yield in these environments. Rate and duration of GF were not associated in these genotypes. Results suggest that simultaneous selection for high GF rate and high kernel weight is possible without lengthening GF duration, and that selection for high GF rate through selection for high kernel weight is possible. High rate and short duration of GF appeared to contribute to increased stress tolerance in these genotypes, but only one of the 20 genotypes investigated had both characteristics. High GF rates with short to medium GF durations appear to be desirable objectives in environments in which the growing season frequently is shortened because of severe stress.