Dissection of grain weight across the oat panicle

The oat ( Avena sativa L.) panicle develops from the tip to apex, resulting in differences in grain weight. A detailed dissection of grain weight across the panicle could reveal information to cope with stress. This study aimed to determine the principal grain‐filling component across the oat panicle and the effect of nitrogen (N) fertilizer dosage. Grain‐filling can be decomposed into grain‐filling rate and grain‐filling duration, as these processes result in different responses on final grain weight depending on the crop species. Experiments were conducted consecutively for 2 yr with seven oat genotypes and four N fertilizer rates. There were differences in the grain‐filling parameters depending on the grain position in the panicle, type of grain (primary or secondary), genotype, and N rate. The heaviest grains had higher initial grain weight and grain‐filling rate. The average grain‐filling rate had a significant linear correlation with grain weight, whereas the effective grain‐filling duration did not. Grain weight, average grain‐filling rate, and grain‐filling onset decreased basipetally. Lower N rates had longer effective grain‐filling duration but decreased the average grain‐filling rate. Our results indicate that the grain weight differences across the oat panicle and genotypes are mainly explained by grain‐filling rate, and there are differences in grain‐filling onset with no change in the effective grain‐filling duration.