Genotype ✕ Year Interaction for Length and Rate of Grain Filling in Oats1

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Abstract
In spring oats (Avena sativa L.) the sensitivity of grain yield to environmental stresses during grain filling varies among genotypes that differ in days to heading. The main objective of this study was to evaluate the relationship between grain yield, grain‐filling rate (GFR), and grain‐filling period (GFP) of oats in two contrasting field environments. A secondary objective was to assess the validity of estimating “vegetative growth rate” (i.e., preheading crop growth rate) from straw weight at maturity and days to heading.Twenty oat genotypes selected for diversity in days to heading and percent groat protein were grown in consecutive years that differed in air temperature during the GFP and in rainfall distribution during the growing season. Average grain yield in 1980 was 8% lower than in 1979. The genotype × year (G × Y) interaction for grain yield resulted from increases from 1979 to 1980 for earlier heading genotypes but decreases from 1979 to 1980 for later heading genotypes. Compared to 1979, the 1980 GFP was shortcned for all genotypes, but was changed the most for later heading genotypes. Relative to 1979 values, GFR in 1980 increased for 12 of the earlier heading genotypes, but decreased for six of the eight later heading genotypes. Kernel weight and groat percentage were also lower in 1980 than in 1979 for all 20 genotypes, supporting the interpretation that kernel growth, and hence grain filling, were curtailed prematurely in 1980.Straw weight declined between heading and maturity for only one genotype in 1979 but for seven genotypes in 1980. Since the occurrence and magnitude of post‐heading change in straw weight are subject to G × Y interaction, vegetative growth rates estimated by dividing straw yield at maturity by days to heading may be invalid. Two alternate methods for more accurately estimating vegetative growth rate are discussed.