Identification Of A Rice Brittle Mutant And Inheritance Of An Early Fixation In Rice

1. Idification of a Rice Brittle MutantPlant mechanical strength is one of the most important agronomic traits in rice, which affect the lodge character. Cell wall is the bone of plant composed of cellulose and hemicellulose and lignin, which is related to plant chemical strength. The BC (brittle culm) genes play an important role in elucidating the synthesis pathway of cellulose and lignin.To date, a great of studies have been made on the brittle culm trait of plant, and about ten brittle culm genes have been reported. Among of which, 5 recessive genes and 1 dominant gene have been reported in rice, and all of them were established on different linkage groups by cytological and classical genetics. A brittle mutant "E532bc"was obtained from the chemical treatment population of E532. E532bc was crossed with japanica and indica rice. The analysis of plant mechanical strength in Fj and Fa populations showed that the brittle trait of E532bc was controlled by two recessive genes. The allelic analysis between mutant genes and BC1 gene indicates that they were nonallelic. The local linkage map of the mutant genes were constructed with Fa population of E532bc crossed with 02428 and molecular marker technique. The results suggested that the brittle genes were located on the long arm of rice chromosome 1 and 7. One gene located on the side of the microsatellite markers RM212 and RM302, and the genetic distances from target gene to the markers, RM212 and RM302, are 11.89cM and 15.19cM respectively. The other gene located on the interval of RM11 and RM234, and the genetic distance from the target genes are 9.36cM and l0.01cM respectively. At the same time, the relative blemish of the mutant were analyzed by using chemical and cytology methods, the results indicated that the mutant genes could reduce the content of cellulose, and lower the strength of plant. These genes, probably being new brittle genes in rice, and designated tentatively as bc-7 and bc-8.2. Inheritance of an Early Fixation in RiceFrom conventional breeding to hybrid breeding, the rice production and quality have improved greatly. But hybrid rice needs production of seeds every year, which wastesmaterial and manpower. The early generation stability found in rice was an exceptive phenomenon found from rice hybrid breeding, which could fix early genotype and be used for many years as a new inbred line, and was important for hybrid breeding.429 and 950 were both the early fixation rice and came from SAR-3 which is a triploid. This study focus on F2 populations derived from 429x9311, 429xR527 and 429x950. It was proved that 4 populations were uniform by using analysis of agronomic characters and SSR markers. The main results as follows.(1) Investigation on agronomic traits showed that, the coefficient of variation (CV) of the 6 agronomic characters, including heading days, plant heights, length of panicles, 1000-grain weights, length of sword-sharped leaf and width of sword-sharped leaf were smaller than or near to that of control variety 429, while the number of productive panicle was not. So these p2 were all early stable populations in agronomic characters.(2) SSR analysis results revealed that these population were all progeny coming from two parents, and the p2 plants present one of the parents bands, not the heterozygous bands, at all of loci. So they were all early stability populations, the uniform phenomenon is homozygous in FI plants, and it was heritable from parents.(3) Analysis the different stable populations come from one hybridized combination, we found that they were not completely identical, but they had variances at many loci. This may be caused by the chromosomal recombination in hybrid, which led to difference appearances among of them.