Genetic analysis of starch paste viscosity parameters in glutinous rice (Oryza sativa L.).

Starch paste viscosity plays an important role in estimating the cooking, eating, and processing quality of rice. The inheritance of starch paste viscosity in glutinous rice remains undefined. In the present study, 118 glutinous rice accessions were collected, and the genotypes of 17 starch synthesis-related genes (SSRG) were analyzed by using 43 gene-specific molecular markers. Association analysis indicated that 10 of 17 SSRGs were involved in controlling the rapid visco analyzer (RVA) profile parameters. Among these, the PUL gene was identified to play an important role in control of peak viscosity (PKV), hot paste viscosity (HPV), cool paste viscosity (CPV), breakdown viscosity (BDV), peak time (PeT), and paste temperature (PaT) in glutinous rice. Other SSRGs involved only a few RVA profile parameters. Furthermore, interactions between SSRGs were found being responsible for PeT, PaT, and BDV. Some of the RVA parameters, including PKV, HPV, CPV, CSV, and PaT, were mainly governed by single SSRG, whereas other parameters, such as BDV, SBV, and PeT, were controlled by a few SSRGs, functioning cooperatively. Further, three near-isogenic lines (NIL) of a japonica glutinous cv. Suyunuo as genetic background, with PUL, SSIII-1, and SSIII-2 alleles replaced with those of indica cv. Guichao 2, were employed to verify the genetic effects of the various genes, and the results were consistent with those obtained from the association analysis. These findings indicated that starch paste viscosity in glutinous rice had a complex genetic system, and the PUL gene played an important role in determining the RVA profile parameters in glutinous rice. These results provide important information for potentially improving the quality of glutinous rice.

Molecular marker analysis and genetic basis for sterility of typical indica/japonica hybrids.

To explore the genes differentiated between typical indica and japonica varieties, two typical indica/japonica varieties, Balilla (japonica) and Nantehao (NTH, indica), were selected to construct genetic populations based on the widely surveying for spikelet and pollen fertility of 90 indica/japonica F1 hybrids, which also were used as the wide compatability testers. In order to analyze the genes (QTLs) related to spikelet and pollen fertility, two reciprocal backcross populations Balilla/NTH//Balilla and Balilla/NTH//NTH were constructed and the spikelet and pollen fertility of each individuals were assessed. In both populations, two traits all appeared distorted normal distribution, but in the first population, they forwarded to low-level fertility type, the later population, forwarded to high-level fertility type relatively. The results indicated that both of male and female gametophytes of Balilla/NTH hybrids were partial sterile. Then we analyzed the SSR marker genotype of each individuals of Balilla/NTH//Balilla population containing 142 individuals, and constructed a SSR linkage map, in which, there were 108 information markers distributing on all 12 chromosomes equably, average marker distance was about 11.9 cM. Therefore the linkage map was qualified for QTL analysis. Two methods were employed to conduct QTLs analysis, i.e., single marker analysis and interval mapping. According to single marker analysis, 17 and 12 markers were found significantly responsible for spikelet and pollen fertility, respectively. And further study by means of MAPMAKER/QTL software, for spikelet fertility trait, two QTLs were detected, qSPTF1 on chromosome 1 and qSPTF6 on chromosome 6, and their additive effect were 13.501 and -16.414, respectively. According to previous studies, qSPTF6 was deduced to be the same locus as S-5. For pollen fertility, qPLLN7 on chromosome 7 and qPLLN9 on chromosome 9 were detected, and their additive effects were -12.003 and -11.012, respectively. Because the QTLs detected cannot explain completely the total variance of mapping population, other genetic factors must be existed to be responsible for spikelet and pollen partial sterility. Hence we let two random markers as putative covariates, and divide the 142 individuals into four groups according to the two marker genotypes, then the average values of spikelet and pollen fertility of each groups were calculated for two-way ANOVA (analysis of variance). The results indicated that there existed strong interaction for both spikelet fertility and pollen fertility. At a significance level of 0.005, there over 61 and 51 pairs loci interactions detected playing an important role in spikelet and pollen sterility expression, respectively. These results indicated that epistasis also was one of major genetic components controlling indica/japonica hybrid sterility.

[Mapping QTLs for horizontal resistance to sheath blight in an elite rice restorer line, Minghui 63].

This study was conducted with a recombinant inbred line (RILs) population consisting of 240 recombination lines, derived from an elite combination, Zhenshan 97B x Minghui 63. The RILs and their parents were grown in a randomized complete design with two replications in the years of 1999 and 2000. Sheath blight response ratings for the population and their parents were identified by an improved method of inoculation, which was carried out with short woody toothpicks incubated with a Rhizoctonia solani strain, RH-9, and inserted the third sheath in the late tillering/green ring stage of growth. A linkage map was constructed from the RILs. The QTL mapping of sheath blight resistance was carried out by the method of interval QTL mapping. Two QTLs for sheath blight resistance were detected in each year, and were located on chromosome 5 and chromosome 9, respectively. The QTL for sheath blight resistance on chromosome 5 was flanked by markers C624 and C246 on the basis of 1999 data, and by markers C246 and RM26 using 2000 data. The 1-LOD-confidence intervals of QTLs for sheath blight resistance on chromosome 5 detected in two years greatly overlapped with each other, and the peak of the 1-LOD-confidence intervals were approximately the same site. This suggested that the QTL for resistance on chromosome 5 detected in 1999 was probably the same as the QTL detected in 2000. The QTL for sheath blight resistance on chromosome 9 was located on the marker interval of C472-R2638 in term of 1999 data, and on the interval of RM257-RM242 based on 2000 data, and the two intervals were 9.7 cM away from each other. Based on the effect analysis of QTLs for resistance, the genotype of MH63 had negative additive effects or reduced sheath blight rating.