One of the most important agronomic problems in rice production (Oryza sativa L.) in high humidity climates is pre-harvest sprouting (PHS). This study was conducted to identify quantitative trait loci(QITs) for PHS resistance using a recombinant inbred (RI) population derived from a cross between a japonica variety Asominori (relatively susceptible to PHS) and an indica variety IR24 (highly resistant to PHS). Knowledge of the genomic positions of QTLs for PHS resistance in rice could greatly simplify selection of the trait.A total of six QTLs for PHS resistance in rice were detected with 289 restriction fragment length polymorphism (RFLP) markers by both one marker analysis (P<0.005) and composite interval mapping (CIM)(LOD>2.0).The two QTLs,located on chromosome 1, accounted for 10.7-20.o% of total phenotypic variations, and the other four QTLs, located on chromosome 4,5,7 and 8,respectively, explained 12.3-25.3% of total phenotypic variation. As a result, four alleles from IR24 on chromosomes 1 (two QTLs),5,7and two alleles from Asominori on chromosomes 4,8 contributed to PHS resistance in rice,respectively.The RFLP markers tightly linked to PHS resistance in rice may be useful for breeding varieties with greater resistance to PHS and adaptable to high humidity climates during the maturation period through the ues of markerassisted selection.

A thermo-sensitve seedling-colour mutant 7436S was detected in the field from a breeding nursery in China, in 1991. The experiments were conducted at artificially controlled temperatures (23.1℃,26.1℃，30.1℃) in growth chambers. The results showed that the seedling colour of the mutant 7436S was white (23.1℃), light yellow (26.1℃) and normal green (30.1℃) at 10 days after sowing and yellwish green (23.1℃) and normal green (26.1℃，30.1℃) at 20 days after sowing, respectively. It was concluded that its thermo-sensitivity decreased gradually with the increase of the seedling age. In addition, its thermo-sensitivity for seedling colour was oriented, as white seedlings turned green at high temperatures, but not in the opposite direction. The segregation ratios in the F2 populations showed that a recessive nuclear gene (tentatively designated as tsc-1) controlled the thermo-sensitive seedling-colour character. Based on genetic linkage and the recombination value (34.1%) between the tsc-1 gene and short panicle morphological marker(sp) gene in the F2 generation, the results indicated that the tsc-1 gene was located on chromosome 11.

Identification and mapping of genomic regions controlling quantitative trait loci (QTLs) was undertaken to determine the genomic regions associated with milling traits in rice to facilitate breeding of new rice varieties with high milling quality. The recombinant inbred (RI) population used was derived from cross of a japonica variety, ‘Asominori’, with an indica variety, ‘IR24’ through 289 RFLP markers. Three milling traits, namely, brown rice percentage (BRP), milled rice percentage (MRP), and milled head rice percentage (MHP), which are the main indicators of milling quality in rice, were estimated for each RI line and their parental varieties. Continuous distributions and transgressive segregations of three milling traits were observed in the RI population, showing that the three traits were quantitatively inherited. Two QTLs (q BRP-9 and q BRP-10) for BRP were identified and mapped to chromosomes 9 and 10, and explained 7.2 and 21.3% of the total phenotype variation, respectively. Two QTLs (qMRP-11 and qMRP-12) governing MRP were detected and mapped to chromosomes 11 and 12, accounted for 12.2 and 7.7% of total phenotype variation, respectively. In addition, three QTLs (qMHP-1, qMHP-3 and qMHP-5) controlling MHP were observed and mapped to chromosomes 1, 3 and 5, and explained 16.0, 22.1 and 8.7% of the total phenotype variation, respectively. Among them, five QTLs (q BRP-9, q BRP-10, qMRP-11, qMHP-3 and qMHP-5) from japonica parent, Asominori, and two QTLs (qMRP-12, qMHP-1) from indica IR24 can improve milling quality in rice. The results and the tightly linked molecular markers that flank the QTL will be useful in breeding for improvement of milling quality in rice.

The development of molecular genetic maps has accelerated the identification and mapping of genomic regions controlling quantitative trait loci(QTL) in rice (Oryza sativa L.). Minimizing embryo size in rice would increase proportion of edible endosperm.This study was conducted to determine the genetic basis controlling embryo size of rice grains in a recombinant inbred (RI) population derived from cross of a japonica cultivar,Asominori,with an indica cultivar,IR24,by means of 289 restriction fragment length polymorphism (PFLP)markers.Two parameters,embryo length and embryo width,which represent embryo size in rice,were estimated for each RI line and their parental varieties.Continuous distributions and transgressive segregations of embryo length and embryo width in rice were observed in the RI population,suggesting that embryo size was quantitative in grains of conventional varieties.Three QTL for embryo length were detected on chromosomes 1, 2, and 3 explained 17.9, 25.7, and 9.2%, respectively, of the total phenotypic variation. Three QTL for the embryo width were observed on chromosome 2, 8, and 10 and accounted for 13.5, 15.7, and 15.0% of total phenotypic variation, respectively. In addition, alleles with increasing and decreasing effects were detected from the both parents. The results and the tightly linked molecular markers that flank the QTL will be useful in breeding for embryo improvement in rice.