| Rice is a staple food for most of the population in the world. Increase of the food production will be mainly contributed by the utilization of the hybrid vigor of rice. Corresponding to rice hybrid seed production, there exist two main systems in China: the traditional three-line system and the novel two-line system. Compared to the former one, the second system, employing photoperiod- and thermo-sensitive genie male sterile (PTGMS) rice as female lines, has many advantages. PTGMS rice has such a broad spectrum of restoration that almost all normal rice strains can restore the fertility of the FI hybrid. Therefore it can be very easily to obtain the ideal hybrid combination without deliberate breeding of restore lines. Moreover, PTGMS lines can not only be used to propagate itself under short-day and relatively, lower temperature conditions but also can be used as female lines for hybrid seed production under long-day and higher temperature conditions. These properties hence win much favor from the breeders of rice variety.However, every PTGMS line must bear a lower critical sterility temperature point (CSTP), which is regarded as the lowermost temperature for PTGMS lines to keep the absolute male sterility status under long-day photoperiod. A high CSTP in the PTGMS line would render the male sterility more susceptible to occasional cool summer days while this line adopted for hybrid seed production develops into panicle differentiation stage, thus causing adulteration of the seeds of PTGMS rice into hybrid seeds. Badly, almost all PTGMS lines used in China, no matter whether they are originally useful ones or not, seem to have the tendency to gradually increase their CSTP and thus producing fertile pollens under the previous sterile conditions. Some originally qualified PTGMS lines therefore have gradually become ineligible after several generations of propagation. This would complicate the two-line hybrid rice breeding and commercialization.This research cast its concentration on the genetic bases and the molecular mechanism of CSTP which underlies the instability of PTGMS lines, firstly deciphering the genetic components by adopting joint segregation analysis of the basic 7 generations based on the iterated expectation and conditional maximization (IECM) algorithm (Gai et al. 2000), and multidimensional discrimination analysis, secondly screening the AFLP linkage markers by in parallel genotyping the parental lines and their consecutive seed deliveries and an F2 population, and thirdly making a conjecture of gene function of CSP1 based on sequencing and bioinformatics analysis, fourthly displaying the expression differentiation of the polymorphic fragment by employing oligo-cappingbased full-length cDNA. The main results are presented as follows.1 F-test and t-test shows that there is no significant difference in fertility between FI' and FI, declaring that the cytoplasm plays no or non-significant effects on the fertility difference of the two parents. Nuclear gene(s) would be the causative factors of the CSTP difference.2 The overall fertilities of the F2 populations in the four temperature regime did not share the same distribution, but decreased as the temperature rising. And there were still some plants that did not follow the trends, but exceptionally getting highest fertility scores at 25.5 or 27.5 . These suggest that these kind of exceptional plants may be the causation that the results from different populations relating to diverse PTGMS lines would be different with each other.3 The IECM algorithm results from the data of 23.5 regime show that there are two dominant major genes and polygene, as well as their respective epistasis conditioning the CSTP under this condition; The two major genes display a high broad-sense heritability ranging from 0.80 to 0.97. And the low CSTP is dominant.4 Screening with 206 AFLP primer combinations indicates that among the 14777 loci screened, only 0.35% of the loci exhibit polymorphism, suggests that the parents are nearly related...
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