Growth of Spring Wheat Kernels as Influenced by Reduced Kernel Number per Spike and Defoliation1

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Abstract
Field studies with the spring wheat (Triticum aestivum L.) cultivars ‘Era’ and ‘OlaF’ were conducted to assess the effects of reductions in kernel number per spike and defoliation of individual culms on kernel growth characteristics. The importance of stage of kernel growth at which treatments were applied was also examined by treating both at anthesis and anthesis + 14 days, the later date being after the beginning of the kernels linear dry matter accumulation period.The effects of the treatments on final weight per kernel depended on the time of treatment and on the relative weights of kernels from the untreated (control) culms. Reduction in kernel number per spike increased final kernel weight, particularly when control weights were low, whereas defoliation always reduced final weight. Treatment at anthesis usually had a larger effect.Growth rates of kernels during the linear dry matter accumulation period were enhanced by kernel removal and depressed by defoliation. Within each genotype, growth rates were highly correlated with final kernel weight. This association, however, differed between years because of variation in length of the grain filling period. No consistent effect of the treatments on grain filling duration was found.The response to early kernel number reduction, as well as the response in additional experiments to spikelet “trimming” suggested that upper limits, or potentials, for both final weight and growth rate were approached. These potential kernel weights and growth rates appeared to depend on genotype, kernel position in a spikelet, and possibly environment.