| To develop good male sterile line with blast resistance,5 maintainer lines, i.e.,1504 (Ganzaoxian 49), IR58025B, Jin 23B, Xinlu B, and Jiangnongzao 2 hao B, were selected as crossing parents. Many sister lines at F5 generation were obtained using cross, multi-cross and systematic selection methods, and then backcrossed with Jin 23 A. during this process, those sister lines were screened and identified simultaneously for blast resistance and preliminary combining ability, and finally bred into the blast resistant male sterile line Ganxiang A and its corresponding maintainer line Ganxiang B.Ganxiang A belonged to temperature-sensitive Indica type rice, and its duration from sowing to initial heading in Nanchang generally ranged from 64 to 77 days. Leaves of Ganxiang A ranged from 12 to 13. Ganxiang A had thin and small anthers, and its pollen was mainly identified as typical abortion with the iodine-treatment and completely abortive. The sterile plant rate and degree of sterility for Ganxiang A both were 100%, and also Ganxiang A exhibited highly stable sterility. Ganxiang A exhibited the stable and uniform agronomic characteristics, were good-looking leaf in ripening stage, no early senescence, heavy 1000-grain weight and aroma. Ganxiang A had better flowering habits and its forenoon flowering rate was 62.9%, the duration of glume opening was longer than that of glume closure. Stigma exsertion rate of Ganxiang A was slightly higher than that of Jin 23 A, which benefited to rice breeding and production. However, stigma vigor of Ganxiang A was slightly worse than that of Jin 23A, thus flowering time of male parents should be 1-2 days earlier than that of female parents in the seed breeding or production program. Ganxiang A was more insensitive to gibberellins 920, accordingly, the dosage of the gibberellins should be slightly increased during rice seed breeding or production.Ganxiang A showed greater resistance to rice blast from Jiangxi, Fujian and Zhejiang provincial rice growing region. In comparison to blast resistant variety Tetep, Ganxiang A was resistant to ZA, ZB, ZC, ZE group and physiological race ZD7, ZG1, and its resistance frequencies ranged from 62.5% to 100%. The comparisons among the reactions of 30 varieties with single resistance gene to 122 rice blast fungus also demonstrated Ganxiang A possess stronger resistance to blast. According to molecular detection, Ganxiang A contained Pi1,Pi5,Pi7,Pi33,Pib,Pita2 genes, which means Ganxiang A had broad spectrum and stable resistance to blast owing to combining multiple resistant genes.Ganxiang A had a better combining ability and all its combinations exhibited hererosis over better parent. All combinations with Ganxiang A shared something in common viz., heavy 1000-grain weight and early mature, but large difference in spikelet fertility. Analyzing yield and its components of the rice combinations with Ganxiang A, some slight differences were found between the middle-season rice and the late season rice as follows:the three most important factors of the middle season rice were spikelet fertility, 1000-grain weight and single panicle weight. As for late-season rice, whereas, the most important factor was 1000-grain weight, followed by effective panicle, and spikelet fertility had a non-significant and negative correlation with grain yield. The requirements for combinations with Ganxiang A were listed as below:the middle-season rice breeding should emphasize the large, heavy panicle type, as well as the high-temperature tolerant combinations with decreasing effect of high temperature on spikelet fertility, to achieve the goal of yield improvement. While the late-season rice breeding should target more at the heavy grain and many panicles type, as well as at the low-temperature tolerant combinations at the booting stage with increasing grain plumpness and 1000-grain weight, to improve yield. Consequently, selection of restorer with high spikelet fertility and heavy single panicle weight is suitable for the middle-season rice; however, selection of restorer with heavy 1000-grain weight, longer panicle, and more spikelet per panicle is suitable for the late-season rice. In rice cultivation, middle-season rice avoid experiencing high temperature as far as possible at the growth sensitive stage, or some measures should be taken to minish effects of high temperature, however, late-season rice should pay more attentions to the total growth period and seed-sowing time, minimizing the effects of low temperature at late growth stage. |
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