The early senescence mutant was isolated from the japonica rice Koshihikari through Ethyl-methane-sulfonate(EMS) mutagenesis. The early senescence phenotype was controlled by a single recessive nuclear gene, tentatively symbolized as es-k. Using phenotypic and molecular markers, we mapped the es-k locus to the long arm of chromosome 7 between STS markers 147-1 and 150-1, a physical region of 370-kb. The symptom of early senescence appeared even before heading, while appeared after heading in those of the wild-type rice during senescence. Early stage physiological characteristics of the es-k mutant was similar to that of the wild-type. However, after heading, es-k mutants started to exhibit a significant decrease in chlorophyll content, soluble protein content 10 days earlier compared to normal type. To characterize the interaction with the environment factors, experiments were carried out under controlled temperature and light conditions, respectively. The wild-type leaf color appeared normal irrespective of temperature treatment, while the leaf of es-k mutant appeared pale-green at the low temperature and dark-green at the high temperature. During dark-induced senescence, mutant did not show significant differences compared to normal type. The results show that es-k is sensitive to temperature but not to light.

This study was carried out to investigate the characteristics of shattering habit and germination of offtype rice plants collected in Korea which were classified into seven groups based on grain characteristics. In the long-grain red rice group, the short-grain red rice group, the long-grain normal rice group, and the long-grain waxy rice group, the tensile strength of grain and primary rachis branch was relatively low and the fiber cell of the primary rachis branch was short. Characteristics of shattering-related traits and germination in relation to grain and esterase isozyme zymogram type of off-type rice plants. In most lines of the extremely late and sterile rice group, the tensile strength of grain was low, while that of primary rachis branch was high, and the fiber cell was long. However, in the type 1 esterase isozyme zymogram(EIZ) lines among the long-grain normal rice group and the type 6 and 5+6 EIZ plants among the extremely late and sterile rice group, the tensile strength of grain was relatively higher. The long-grain waxy rice group and the type 3 EIZ lines among the long-grain red rice group, showed higher germinability than did cultivars which are known to germinate well even in low-temperature. The other off-type rice group, except for the short-grain waxy rice group and type 1 and 7 EIZ lines among the long-grain normal rice group, had higher germination speed than that of the cultivars.