Mechanism of Grain Notching, and Variation for Notched Grain Frequency in Rice

[摘要] Although the size and shape of the caryopsis in rice plants are determined by the capacity of the glume, the growth of the caryopsis and the floral glumes may be controlled by different genetic systems and thus they may have different developmental paths. Therefore, in varieties having potentially much longer caryopsis than the glume, the growth of the caryopsis may be affected by the glume leading to abnormal grain formation. One of such abnormal development of caryopsis is "notched" grain which is observcd with variable frequencies in some of the rice varieties. This investigation reveals an account of the mechanism of grain notching and the variation for notched grain frequency in rice. A total of 32 varieties and lines was grown in glasshouse as well as in field to investigate the varietal and environmental variation for the notched grain frequency and also the correlation of notched grain percentage with the unbalance between the length of the caryopsis and the glume. For allowing the caryopsis to grow freely, the top of the glume on one or two panicles in each of the plants was clipped off at two or three days after the anthesis. In the field, glume clipped panicles were protected by parchment paper bags. The length of glume-clipped caryopsis (T1) and untreated one (C1) were measured using ten caryopses randomly taken from each of the 6 plants in glasshouse and 20 plants in the field. T1/C1 ratio was calculated to indicate the degree of unbalance between the potential length of caryopsis (T1) and the longitudinal capacity of glume (C1). One hundred untreated caryopses from each of the plants were exarnined to determine the percentage of notched grain. The percentage was transformed into the degree of angle for the statistical analysis. Correlation between the T1/C1 ratio and the notched grain percentage was also analyzed. Varietal variation ranged from 0 to 90% for notcched grain and from 1.1 to 1.5 for T1/C1 ratio which indicated that the potential length of the caryopsis was 1.1 to 1.5times more than the longitudinal capacity of the glume. From these results, the materials used were classified into three groups: Group A, showing remarkably high, more than 80%, grain notching and high T1/C1 ratio in both the glasshouse and field conditions, group B, showing highly sensitive response of grain notching to the environmental conditions, and group C, showing mostly normal grains with low T1/C1 ratio. The glume-clipped caryopsis did not develop notched grain in all of the materials. Correlation between the glasshouse and field was high for C1 and T1, but it was rather low for notched grain percentage and thc T1/C1 ratio in some varital groups. Highly significant correlation between notched grain percentage and T1/C1 ratio (r=0.94) suggested that unbalance between the length of glume and caryopsis was the primary factor determinig the grain notching. From these studies, it may be concluded that, along with other factors, abnormal growth of the caryopsis restricted by the glume capacity results in notching of the caryopsis.

[学科分类] 农业科学（综合）