Mapping QTL for Heat-Tolerance at Grain Filling Stage in Rice

A mapping population of 98 lines (backcross inbred lines, BILs) derived from a backcross of Nipponbare/Kasalath// Nipponbare was planted at two experimental sites, Nanjing and Nanchang, and treated with high and optimal temperature during grain filling, respectively. The grain weight heat susceptibility index [GWHSI= (grain weight at optimum temperature-grain weight at high temperature) / grain weight at optimum temperature × 100] was employed to evaluate the tolerance of rice to heat stress. A genetic linkage map with 245 RFLP markers and a mixed linear-model approach was used to detect quantitative trait loci (QTLs) and their main effects, epistatic interactions and QTL× environment interactions (Q×E). The threshold of LOD score=2.0 was used to detect the significance of association between marker and trait. A total of 3 QTLs controlling heat tolerance during grain filling were detected, on chromosomes 1, 4 and 7, with LOD scores of 8.16, 11.08 and 12.86, respectively, and they explained the phenotypic variance of 8.94, 17.25 and 13.50 %, correspondingly. The QTL located in the C1100-R1783 region of chromosome 4 showed no QTL× environment interaction and epistatic effect, suggesting that it could be stably expressed in different environments and genetic backgrounds, and thus it would be valuable in rice breeding for heat tolerance improvement. This QTL allele, derived from Kasalath reduced 3.31% of the grain weight loss under heat stress. One located between R1613-C970 on chromosome 1 and the other between C1226-R1440 on chromosome 7, with additive effect 2.38 and 2.92%, respectively. The tolerance alleles of both these QTLs were derived from Nipponbare. Both of these QTLs had significant QTL× environment interactions, and the latter was involved in epistatic interaction also. Eight pairs of epistatic effect QTLs were detected, one pair each on chromosomes 1,2,3, 5, 7, 8, 10 and 12. The results could be useful for elucidating the genetic mechanism of heat-tolerance and the development of new rice varieties with heat tolerance during grain filling phase.

Mapping of a New Gene Wbph6(t) Resistant to the Whitebacked Planthopper, Sogatella furcifera, in Rice

A rice population consisting of 90 TN1/Guiyigu F3 lines was employed to analyze the linkage between DNA markers and a new gene Wbph6(t) conferring resistance to whitebacked planthopper, Sogatella furcifera By using the mapping approach of bulked extremes and recessive class, Wbph6(t) was mapped onto the short arm of chromosome 11 with a genetic distance of 21.2 cM to SSLP marker RM167.

Progresses in Researches of the Application of Low-Amylose Content Rice Gene for Breeding

Amylose content is a key determinant of eating quality of rice. With the characteristics offluffy texture, glossy appearance when cooked, remaining soft when cooled and excellentpuffing ability, the low-amylose rice with amylose content 5-15% could be served as not onlycooked rice directly, but also good material for convenience, mixed rice and puffing foods.Current status on characterization, inheritance, molecular mechanism and breeding of low-amylose content rice was reviewed in this paper, strategy of related researches in the era ofglymics was mainly discussed furthermore. The future research should focus on screening andenhancing the germplasm, further elucidating the molecular mechanism on mutation of lowamylose content, utilizing the genes independent of Wx on low-amylose content rice breedingprogram, and developing high quality functional rice cultivars for special usage throughpyramiding low amylose gene and other special quality genes.

Analysis on Stability of AC,GT and PC in Rice Varieties (Orzya sativa L.)

The investigation of rice varieties stability for amylose content (AC), gelatinization temperature (GT) and protein content (PC) was carried out using additive main effects and multiplicative interaction (AMMI) model in three locations and two years. Eighteen tested varieties were further clustered and evaluated based on the phenotypic values of three quality traits and their Di values from the AMMI analysis. The results showed that the genotype by environment interactions, the differences of phenotype and stability of AC, GT and PC among different genotypes and environments were all significant at 1% level. Also, only one variety, W002, had high stability for all the three quality traits. Additionally, in consideration with the phenotype of AC, GT and PC, and their stability in rice varieties, etc., four rice varieties, W002, Zaofeng 9, Guangling Xiangjing and Nanjing16, could be also applied as breeding parents to improve eating quality and stability of rice.

Analysis of QTL for Seed Dormancy and Their Response to Dry Heat Treatment in Rice (Oryza sativa L.)

Quantitative trait loci (QTL) controlling seed dormancy in rice were identified usingrecombinant inbred lines (RILs) population derived from the cross between a japonicavariety Kinmaze and an indica variety DV85. Seeds of two parental cultivars and each RILwere harvested in 35d after heading. The germination percentage of these seeds at 30℃for 7 days were measured as the degree of seed dormancy. QTL analysis was performed withWindows QTL Cartographer 1.13a program by composite interval mapping. A total of four QTLfor seed dormancy were detected on chromosome 2 (two regions), 5 and 11, respectively.Phenotypic variation explained by each QTL ranged from 8.37 to 17.40%. Responses of suchloci to a dormancy-breaking treatment with dry heat were further detected. The resultsshowed that two alleles of qDOR-2-1 and qDOR-5 from DV85 as well as the allele of qDOR-11 from Kinmaze increased the seed dormancy, which seemed to be easily broken by dry heattreatment. Such loci of seed dormancy may be applied to rice genetic improvement. Theallele of qDOR-2-2 from DV85 increased the seed dormancy, which could not be broken bydry heat treatment.

Mapping Quantitative Trait Loci for Palatability of Milled Rice

Quantitative trait loci (QTLs) controlling palatability in rice were identified using a set of 98 backcross inbred lines (BILs) population derived from a cross between a japonica variety Nipponbare and an indica variety Kasalath. The palatability scores of the population measured by RQ1/Plus Rice Analyzer, showed a continuous and transgressive segregative distribution with a range from 66 to 92. Four putative QTLs for palatability, qPAL-5, qPAL-7, qPAL-8a and qPAL-8b, were detected on chromosome 5, 7 and 8, and they accounted 7.83, 7.03, 11.58 and 7.19% of the total phenotypic variation, respectively. Three alleles qPAL-5, qPAL-7 and qPAL-8b from Kasalath increased the palatability score, whereas only one Nipponbare allele qPAL-8a increased the score . Eight transgressive lines in palatability were selected to make a comparison between phenotypic and genotypic classes. The result explained the possibility of positive QTLs pyramiding through marker-assisted selection of highly palatable rice.

Effect of Temperature on Pollen Fertility in Inter-Subspecific Rice Hybrids

Seventeen rice varieties and hybrids of different types (indica, japonica, javanica, indica hybrid, japonica hybrid and inter-subspecific hybrid) were evaluated to determine the effect of temperature on pollen fertility in inter-subspecfic hybrids. The pollen fertility of inter-subspecific hybrids was greatly reduced when average daily temperature dropped to 22.0 - 23.0℃ at meiosis stage, and the extent of pollen fertility reduction varied greatly with respect to different hybrids. However, the pollen fertility reduction of indica and japonica hybrids and conventional varieties was not obvious under the same regime of temperature conditions. When the average daily temperature dropped to 20℃, the pollen development of conventional varieties and hybrids was also affected. Correlation analysis revealed that there existed a positive correlation between pollen fertility and average daily temperature. A significant difference (P<0.01) was also found between the two correlation coefficients i.e. inter-subspecific hybrids and conventional varieties. Temperature at meiosis stage of pollen mother cell was a key factor in pollen developing, and the pollen fertility of inter-subspecific hybrids was more sensitive to low temperature than that of traditional variety.

Mapping and Analysis of Quantitative Trait Loci Controlling Seed Dormancy in Rice

Seed dormancy is one of the most important traits related to the rice grain quality and seeds application, because it is associated with pre-harvest sprouting, resulting in a downgrading of quality and severe limitations in end-use application. The recent development of DNA markers and linkage maps of rice has made possible mapping of individual genes associated with complex seed dormancy traits, analyzing the genetics effects of individual genes and genotype-by- environment interactions. Up to now, numerous quantitative trait loci (QTLs) associated with seed dormancy in rice have been identified and mapped in the molecular genetic map by different populations. In this review, we focus on the genetic base of seed dormancy in rice, especially compare QTLs controlling seed dormancy reported up to now, analyze the expression and stability of QTLs controlling seed dormancy, and discuss the present problems. Finally we show a new pathway to further research on seed dormancy.