| The objectives of this study were to investigate the ratooning characters of rice and to determine the relations between its ratooning ability and physiological factors such as endogenesis plant hormone. One rice variety and three hybrid combinations, which had high yield potential with high ratooning ability, were screened from 32 rice varieties (hybrid combinations, HC). The relations of ratooning abi lity to the yield and yield components of'the main crop (MC), to endogenesis plant hormone, activity of superoxide dismutase (SOD) and peroxidase (POD) of MC root and culm both on day 18 after heading and on day 7 after harvesting of MC were examined. The dynamic changes of endogenesis plant hormone, the activity of SOD and POD of rice culm during the ratooning period were comparatively studied by using two hybrid combinations Peilangyou 500 that has high ratooning ability and Shanyou 63 which used as a control. Additionally, the reutilization of heterosis for ratooning rice, selective index for ratooning rice breeding, the mechanism of endogenesis plant hormone to ratooning, the relation of ratooning properties and SOD and POD, the relation of ratooning properties and internode characters were discussed. The main results of this study are summarized as following.1) The average yields of MC and the ratoon crop (RC) of hybrid combinations increased by 13.059%, 5.377% respectively, compared to those of inbred varieties, showing that ratooning cultivation of hybrid rice can be a potential way for reutilization of heterosis.2) Analysis of variance showed that there were significantly (p<0.01) differences of yield among the experimental materials. The yields of ten rice varieties (HC) such as Zhunliangyou 198, 8015S/288, PeiliangyouSOO, 8015S/559, 316A/80, Pel' ai64S/qingzhen and Pel' ai64S/E32 were reached 10t/hm2. The former three varieties, with high yield compared to Shanyou 63, can be used as high yield combinations for ratooning cultivation. Variety 198 with great ratooning ability and yield potential, can be used as parent in ratoon rice breeding.3) The total grains per panicle, seed setting percentage and grainweight of RC were significantly (P<0. 01) related to corresponding yield components of MC. The seed setting percentage of MC, which is positive related to RC yield and is reflecting the source-sink relation of MC, can be an index for choosing ratoon rice varieties (HC).4) The number of ratooning panicles per hill of the male parent was significantly (P<0.05) related to the number of ratooning panicles, ultimate ratooning rate (Ultr. Ra) and the yield of ratooning crop of F,. The total grains and seed setting percentage of RC for male parent were significantly (P<0. 05) related to those for F,.5) There were great differences in ratooning rate among the experimental materials, with the minimum ratooning rate of 0.808 and maximum of 2. 140. The development of rice ratoon was also various with varieties. The experimental materials (n=31) can be classified as the following three groups by hierarchical cluster analysis according to the ratooning rate of different stages.Group I : Varieties (HC) with high ultimate ratooning rate and early ratooning development.Group II: Varieties (HC) with high ultimate ratooning rate and late ratooning development.Group III: Varieties (HC) with low ultimate ratooning rate and late ratooning development.6) The rice ratooning ability was significantly (P<0. 05) related to the content of abscisic acid (ABA) and zeatin (ZR) and to the content ratio of ABA to [indole acetic acid (IAA) + gibberellin (GA)] and (IAA+GA+ZR) in the culm before harvest of MC, whereas the content of IAA and the content ratio of promotional plant hormones to ABA were positively correlated to rice ratooning ability after harvest of MC.7) Dynamic analysis of endogenesis plant hormone during the ratoon development stage showed that the content of ABA, IAA, ZR and the ratio of promotional plant hormone to ABA were the main factors inducing ratoon developing. The rice rat...
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