Temperature Response of Notched Grain Percentage in Rice

Abstract

The occurrence of notched grain in rice is certainly a genetic trait, but is markedly affected by environmental factors such as temperature after heading. To investigate the en-vironmental variation in notched grain occurrence, the F₂ plants and the progeny lines derived from a cross between a highly notching line L-45 and a normal Japanese cultivar Akiminori were grown at various conditions. In the first part of the study, the F₂ plants were grown at 14 different conditions (Table 1). The percentage of notched grain and caryopsis length were determined for each F₂ plant, and heading date was recorded for each F₂ population as a whole. The range of heading date within each population was about 10 days. Records were also taken for daily maximum, daily minimum and daily mean temperatures during the caryopsis elongation period, which was represented by the average temperature during 15-day period starting from the heading date of the earliest plant among the population. In each F₂ population, the percentage of notched grain showed a continuous distribution. The distribution pattern markedly differed according to growing conditions, namely, the percentage of plants with notched grain varied from 25 to 100%, and the maximum notched grain percentage within a population varied from 43 to 100%. The population mean of notched grain percentage was as high as 58% when it was grown at Kurashiki in late season, while it was only 1.5% in mid-season cropping.