[Correlation of intersubspecific hybrid rice spikelet fertilization rate with temperature and related statistic model].

Using four types of rice, i. e., indica-japonica hybrid, intermediate hybrid, indica and japonica cultivars as test materials, this paper studied the sensitivity of intersubspecific hybrid rice to climatic factors, and the correlations between spikelet fertilization rate (SFR) and daily meteorological factors during 2000 and 2001. The results showed that the SFR of intersubspecific hybrids was lower than that of indica and japonica cultivars. Among eleven meteorological factors, temperature was the key factor, and the mean temperature within five or seven days around panicle flower blooming affected the SFR significantly. A comprehensive model of SFR-temperature was established, with which, the fittest temperature and safe temperature for fertilization of intersubspecific hybrids was estimated to be 28.2 - 29.3 degrees C and 23.4 - 24.3 degrees C, 2.2 degrees C and 1.5 degrees C higher than those of indica and japonica cultivars, respectively. It was suggested that the safe heading date for planting intersubspecific hybrid should be moved up to the last ten-day of September to the first ten-day of October in southern China, the first ten-day of September in middle and lower reaches of Yangtze River Valley, and the last ten-day of August to the first ten-day of September in rice planting area between Yangtze and Huai River.

[QTL analysis of low-temperature-sensitive pollen sterility in Indica-japonica hybrid rice (Oryza sativa L.)].

There existed a number of biological constraints in exploiting the heterosis of indica-japonica hybrid rice. The low-temperature-sensitive sterility (LTSS) of indica-japonica hybrid has become one of the major problems in indica-japonica hybrid rice breeding after the solution of poor fertility of the hybrids by the finding of wide-compatibility gene. Previous studies revealed that the LTSS might be caused by low-temperature-sensitive pollen sterility (LTSPS). However, the genetic basis of LTSPS remained unclear. To explore the genetic basis of LTSPS in indica-japonica hybrid rice, an F2 genetic population derived from 3037 (indica) and 02428 (japonica) was developed. At the booting stage, pollen fertility of F2 population together with parents were surveyed after the treatment with low temperature daily average of 21-23 degrees C. The linkage map was constructed containing 108 SSR markers distributed throughout the whole 12 chromosomes with average marker interval of 16.26 cM. Using software MapMaker/QTL, two putative QTLs, namely qLTSPS2 and qLTSPS5 on chromosomes 2 and 5 were detected by interval mapping, which could explain the phenotypic variation 15.6% and 11.9% respectively. The additive effects were 0.021 and 0.045, dominant effects were -0.246 and -0.215, and the degrees of dominance were 11.7 and 4.8, respectively for the two QTLs. Therefore, the mode of gene action in response to low-temperature stress was overdominance and LTSPS was mainly the result of interaction between the indica and japonica alleles within each locus. In addition, two-way ANOVA showed that the two QTLs acted essentially independent of each other in conditioning LTSPS.

[Inheritance of bc1 gene in intersubspecific hybrids of rice (Oryza sativa L.)].

Distorted segregation of the brittle culm-1 gene (bc1) on rice chromosome 3 was found with greatly increased or decreased frequency of bc1 bc1 genotype in inter-subspecific hybrids, although the gene normally transmitted to its offspring following the Mendelian Law in intra-subspecific hybrids. In a combination of Kamairazu//Ketan Nangka/Kamairazu,an increased frequency of bc1 bc1 in F1, normal segregation in F2, and increased and decreased frequency in a few F3 and F4 lines were observed. In a cross of IR36/Kamairazu, decreased frequency in F2, both normal and decreased segregations in F3 and F4, and a few lines of increased ratio in F4 were found. In F2 of Ketan Nangka/IR36//Kamairazu, increased and decreased and normal segregations were all observed. There was no significant correlation between the frequency of bc1 bc1 and pollen fertility. It implied that distorted segregation of bc1 was caused by selective fertilization of male gametes, which were governed by gametophyte genes of ga2, ga3 and ga14 on chromosome 3.