Tsukasa Nagamine

Diversity in phenotypic profiles in landrace populations of Vietnamese rice: a case study of agronomic characters for conserving crop genetic diversity on farm

Phenotypic variation of agronomic characters in aromatic rice (Oryza sativa L.) was analyzed in order to elucidate the genetic diversity of the populations of rice landraces. Thirteen populations in Namdinh province, in the Red River Delta of Vietnam, were studied in both of farmers fields and an experimental field. Only small differences were found in agronomic characters among the populations, including populations containing different varieties. Variations among the populations in the frequency distributions of several characters suggested different degrees of diversity among the populations even among populations with the same variety name. The phenotypic profiles of farmers fields were different from those in an experimental field suggesting the environmental differences between them. One variety cultivated in the Myloc district had different phenotypic characters from the other varieties in the Haihau district more clearly in the experimental field. Since the small phenotypic variation in each of farm might be due to the genetic drift and selection by the farmers, on farm conservation of the landraces of rice is considered to be under a force to decrease phenotypic diversity. The present study suggests that the targeting several farms with different phenotypic profiles contribute to the conservation of regional genetic diversity of the landraces of rice.

Genetic analysis of a null-allele for lipoxygenase-3 in rice seeds

SummaryLipoxygenase (LOX) catalyzes peroxidation of lipids in rice grains and is related to the formation of volatile compounds. We report on the mode of inheritance of LOX-3 in the rice variety Daw Dam. This variety lacks the LOX-3 (Suzuki et al., 1993), which is a major isozyme in rice seeds. The inheritance of LOX-3 in rice seeds was determined by crossing Daw Dam with rice cultivars having normal LOX-3 activity. The distribution of F2 phenotypes for the presence and absence of LOX-3 from selfed F1 plants fitted the ratio 3:1. Segregation ratio of the B1F1 generation gave a good fit to 1 presence of LOX-3: 1 absence. These data support the hypothesis that the lack of LOX-3 is recessive to the presence of LOX-3, and we conclude that the absence of LOX-3 is inherited as a single recessive trait. We discuss the possible use of the LOX-3 less mutation in relation to volatile compounds production in rice grains.

Development and Utilization of Isogenic Lines Koshihikari Toyama BL

Six isogenic lines with complete resistance genes (R-genes) on the genetic background of the japonica rice variety Koshihikari were developed. BL1 has Piz-t, BL2 has Pii and Pita-2, BL3 has Pib, BL4 has Pik-p, BL5 has Pik-m, and BL6 has Piz and Pia, respectively. We adopted these lines for mixed planting, because we expected them to have a barrier effect. Based on the distribution of the blast race, we determined that we should mix BL 1, BL2 and BL4 in a ratio of 4, 4 and 2. After mixing, we investigated the barrier effect under moderate and heavy epidemics of disease. The barrier effect was confirmed under the moderate conditions even when the mix contained 40% of the susceptible variety, but the ratio of the susceptible variety could only be 20% under the heavy conditions. This suggests that the mixing ratio of the susceptible varieties should be restricted to within 20% under a heavy blast epidemic. Furthermore, BL showed strong resistance to the panicle blast that occurred during the ripening period. In this case, the BL yield was 1.7 times as high as that of Koshihikari.

Genetic Dissection and Mapping of Genes Conferring Field Resistance to Rice Blast in Japanese Upland Rice

Field resistance to rice blast in Japanese upland was analyzed genetically. Chromosomal regions that are involved in field resistance were detected by quantitative trait loci (QTL) analysis using F4 lines of a cross between resistant upland rice variety Owarihatamochi and susceptible irrigated rice variety Nipponbare. At two QTLs on chromosome 4 and one on chromosome 12, alleles from Owarihatamochi were resistant, while an allele from Nipponbare was resistant at one QTL on chromosome 9. Backcrossed progeny lines with each of the resistant alleles from upland rice were developed using the highly susceptible irrigated rice cultivar Aichiasahi as the recurrent parent. At all three QTLs, the lines with the Owarihatamochi allele showed a significantly higher level of field resistance than did those with the Aichiasahi allele. The differences in resistance between two genotypes were largest at the QTL on chromosome 4 and smallest at the QTL on chromosome12, in good accordance with the result of QTL analysis. The QTL of largest effect on chromosome 4 was mapped as a single recessive gene designated as pi21 by genetic linkage analysis. Using a mapping population consisting of 82 lines, we located pi21 between marker loci G271 and G317 at a distance of 5.0 cM and 8.5 cM, respectively. High-resolution genetic linkage analysis using 1104 individuals identified several DNA markers tightly linked with the pi21locus. These markers are being used to identify P1 artificial chromosome (PAC) clones containing this locus for positional cloning of pi21.