Estimating Out-Crossing Rate of Bg 379-2 Using Morphological Markers and Confirmation by Molecular Markers

Rice is largely self-fertilized and accordingly a field population of rice is completely composed of near homozygotes. Due to the emergence of off-types, homozygosity will be affected. With the time, this will cause the reduction of genetic purity in some rice varieties. One of the reasons has been suspected to be the high out-crossing frequencies of such varieties. Studies were conducted at the Rice Research and Development Institute, Batalagoda, Sri Lanka to estimate the out-crossing rate of Bg 379-2, a variety having the problem of maintaining genetic purity. Bg 379-2 was allowed to out-cross with Bg 450 and the number of out- crossed plants were counted using dominant morphological markers such as short-round grain and purple culm of pollen donor. A molecular confirmation of out-crossing was also performed using sequence tagged site （STS） molecular marker pTA248. The variety Bg 379-2 showed a potential out-crossing rate of 3.41% and an average out-crossing rate of 1.29% using dominant morphological markers. Polymorphism was cleady detected between parents and out-crossed plants as well as selfed plants of Bg 379-2 using their banding patterns. A similar study can be performed to determine the out-crossing rates of other varieties which show high percentage of off-types in the population for the better understanding of the breeding behavior of the varieties.

Nectar secretion of RN-type cytoplasmic male sterility three lines in soybean [Glycine max(L.) Merr.]

Significant progress has been achieved in the use of heterosis in soybean and several soybean hybrids have been released in China. However, broad use of hybrid soybean seed is limited due to low seed setting of female parents. Breeding cytoplasmic male sterile（CMS） lines with high out-crossing rate is necessary to solve the problem. The objective of this study was to determine the relationship between out-crossing rate of CMS lines and their nectar secretion. The daily nectar secretion rhythm, meteorological effect on nectar secretion, and differences in nectar secretion among genotypes and years were investigated in 27 soybean CMS lines（A-lines） with their maintainers（B-lines） and restorers（R-lines）. The correlation between out-crossing rate of CMS lines and nectar production was also evaluated. Nectar secretion had diurnal variation. Secretion initiated at about 06：00 for most materials and reached a peak at 07：00–08：30 after flower opened, then the nectar secretion decreased gradually. A sub-peak appeared at about 13：00, while the nectar could not be detected at 17：00. Nectar secretion was greatly influenced by the weather conditions. The amount of nectar secretion increased gradually over time during periods of high temperature and no rainfall for several days. Rainy weather and low temperatures inhibited nectar secretion. There were obvious variations of nectar amount among different genotypes tested. Significant nectar variation within a genotype among years was also observed, and the highest nectar secretion was 3-fold higher than the lowest. The amount of nectar secretion from R-lines was significantly higher than that of A-and B-lines. There was no significant difference in nectar secretion between A-and B-lines. A-and B-lines with higher out-crossing rates secreted more nectar. The amount of nectar secretion of A-and B-lines were significantly positively correlated with the out-crossing rate of A-lines.

Genetic Analysis and QTL Mapping of Large Flag Leaf Angle Trait in Japonica Rice

Genetic segregation analysis for flag leaf angle was conducted using six generations of P1, P2, F1, B1, B2 and F2 derived from a cross of 863B （a maintainer line of japonica rice） and A7444 （a germplasm with large flag leaf angle）. Genotypes and phenotypes of flag leaf angle were investigated in 863B （P1）, A7444 （P2） and 141 plants in BC^F~ （863BIA744411863B） population. An SSR genetic linkage map was constructed and QTLs for flag leaf angle were detected. The genetic map containing 79 information loci was constructed, which covers a total distance of 441.6 cM, averaging 5.6 cM between two neighboring loci. Results showed that the trait was controlled by two major genes plus polygene and the major genes were more important. Fifteen markers showed highly significant correlations with flag leaf angle based on single marker regression analysis. Two QTLs （qFLA2 and qFLA8） for flag leaf angle were detected by both composite interval method in software WinQTLCart 2.5 and composite interval method based on mixed linear model in QTL Network 2.0. The qFLA2 explained 10.50% and 13.28% of phenotypic variation, respectively, and was located at the interval of RM300 and RM145 on the short arm of chromosome 2. The qFLA8 explained 9.59% and 7.64% of phenotypic variation, respectively, and was located at the interval flanking RM6215 and RM8265 on the long arm of chromosome 8. The positive alleles at the two QTLs were both contributed from A7444.