| The acreage of two-line hybrid rice has been increasing year after year due to the advantages of free combinations, high quality and high yield. However there are some problems related to its production and application. The main issue of two-line hybrid rice was the sensitivity of the two-line male sterile line to low temperatures. When abnormally low temperatures coincide with its temperature sensitive period, it would reverse to various degrees of partial fertility, which leads to a reduction in purity of the two-line hybrid rice. This situation constitutes a potential risk to the production of a pure line seed. In this study, Pei'ai 64S dry seeds were exposed to a 300Gy dosage of 60Co gamma radiation, and a leaf color mutant at seedling stage was found. The characteristics of this mutant were similar to those of Pei'ai 64S except for the leaf color at seedling stage. This leaf color marker could be reliably used in the rapid identification and elimination of the sterile seedlings and this will constitute an effective measure to reduce the risks and losses from fertility reversion in the production of hybrid rice. Genetic control, mutant gene mapping, agronomic traits, fertility characteristics, combining ability, grain quality, disease resistance of the leaf color marker, and its application to purity detection were systematically investigated in current study.The main results are/were as follows:1. Various leaf color mutants at the seedling stage, such as albino, zebra and pale-green were obtained after 60Cobalt gamma rays irradiation,. Some of the mutants exhibited the leaf color mutation through their whole growth period, while others displayed special colors at the seedling stage and recovered normally after 4-5 leaves.2.Compared to other mutants, whose negative reaction to the radiation was high (even resulting in the death of some mutants at seedling stage), the negative effect of the radiation on the green-revertible albino mutant (which was similar to the original sterile line in agronomic traits) was very small. There was a correlation in leaf color changes of the green-revertible albino mutant to changes in temperature; the time to resume normal color was longer under low temperature, while it became shortened at high temperature. The percentage of albino leaf area was also correlated to temperature. Within the normal temperature range for rice growth, the lower the temperature was, the more obvious the marker expression became as was shown by an increase in the percentage of albino leaf area.3.Allelism of the mutant genes was conducted by the crosses between different mutants. The results indicated that most of F1 displayed a normal green color, which suggested that only small part of the mutant genes were allelic. Genetic analysis showed that the leaf color mutant was controlled by a single recessive nuclear gene.4.We had successfully bred a novel two-line sterile line Biao 8S, which was a green-revertible albino in the seedling stage. The sterile line had the characteristics of albino at the 1-3 leaf stages, changing to green after an extension of the 4th leaf. The agronomic traits, disease resistance and free combination of Biao 8S were very similar to that of Pei'ai 64S. Biao 8S had a more improved external appearance, lower amylase content and gel consistency, and a higher protein content compared to Pei'ai 64S.5.During the multiplication and production of Biao 8S hybrid rice, the identification and removal of green seedlings without this obvious leaf color marker could ensure the propagation of sterile seed lines and preserve the purity female parents,.6.This method is feasible for the rapid determination of hybrid rice purity by removing the mixed albino Biao 8S seedlings. |
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