Lipoxygenase (LOX) is thought to play an important role in the formation of desirable or undesirable flavor and aroma in many plant products. In rice seeds, LOX activity is localized in the bran fraction and LOX-3 is the major isozyme component. We used gas chromatography-mass spectrometry to determine whether the degree of staleness in the flavor of stored brown rice was related to the presence of LOX-3. We found that the amount of hexanal, pentanal, and pentanol in normal raw LOX-3 rice markedly increased during storage at 35 degrees C. That in LOX-3-less rice increased slightly but was a third to a fifth that of normal LOX-3 rice. In cooked rice, the amount of these components from glutinous rice exceeded that in nonglutinous rice, and that in normal LOX-3 rice exceeded that in LOX-3-less rice. These results indicate that the stale flavor production in LOX-3-less rice during storage is less than that in normal LOX-3 rice.

This study focused on a Yunnan landrace of rice, Kunmingxiaobaigu, to identify quantitative trait loci (QTLs) controlling cold tolerance at the reproductive stage using DNA markers. A linkage map with 16 linkage groups covering 1,354.4 cM with a total of 122 markers was constructed based on an F 2 population consisting of 250 individuals of a cross between Kunmingxiaobaigu and a Japanese variety, Towada. Nine QTLs were detected by interval mapping in the F 2 population. The nine QTLs were distributed on chromosomes 1 (2 QTLs), 3, 4, 6 (2 QTLs), 7, 10 and 12. The total variance explained by these nine QTLs was 54.2 %, while the variance explained by a single QTL ranged from 5.0 % to 37.8 %. The validity of four QTLs on chromosomes 3, 6 (2 QTLs) and 7 was confirmed by single-marker analysis in the F 3 population and they were designated as qRCT3, qRCT6a, qRCT6b and qRCT7, respectively. The QTLs qRCT3, qRCT6a and qRCT6b were reported here for the first time. The QTL qRCT7 displayed the largest effect, reaching a value of 20.6 %.

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An incompletely dominant gene Ur1 (Undulate rachis -1) increases spikelet number per panicle, and can enhance grain yield by enlarging sink size. The yield-increasing effect of Ur1 was examined on five different genetic backgrounds. The Ur1 isogenic line of 'Nishihikari' (N U ) has been developed by successive backcrossing. 'Nishihikari' (N) has the highest lodging-resistance in southern Japan. This isogenic line, N and their F 1 possessing the Ur1/+ genotype (N H ) were grown in 2000. The yield of the three genotypes was in the order N U > N H > N, though the difference between N U and N H was not significant. Ur1 increased spikelet number per panicle by 29 and 24%, respectively, in N U and N H , whereas Ur1 decreased panicle number per m 2 , ripened-grain percentage and 1000 grain weight by the ranges of 4 to 8% and 4 to 6%, respectively, in N U and N H . From the F 1 of N × the isogenic line of 'Taichung 65' carrying both Ur1 and sd1-d, four isogenicline pairs (e.g. 27 U and 27 + ) were developed after maintaining the heterozygosity (Ur1/+) to F 8 or F 9 generation. These four number-named isogenic-line pairs, N U and N were planted under a field condition in 2001. Analysis of variance indicated that the effects of Ur1, genetic background and the interaction were significant in yield. The five Ur1-carrying isogenic lines had a varying yield from 752 (N U ) to 542 (30 U ) g/m 2 . The yield increase by Ur1 ranged from 250 g/m 2 (61%) to 75 g/m 2 (16%). In spikelet number per panicle, the increase by Ur1 ranged from 62.1 to 39.2, while the percentage increase varied from 90 to 42%. The spikelet-increasing effect of Ur1 was greater on a small-panicled genetic background than on a large-panicled genetic background. Ur1 decreased ripened-grain percentage by 17% in 30 U , relative to 30 + , whereas no significant decreases were noticed in the other four Ur1-carrying isogenic lines. Ur1 increased culm length in 27 U , 52 U and 74 U , whereas no increase was noticed in N U and 30 U . It is concluded that N U could be a prospective material for developing high-yielding japonica varieties carrying Ur1, from the viewpoint of lodging tolerance as well as yield.