ABSTRACT
To find new QTLs responsible for kernel cracking resistance, we screened 50 CSSLs derived from the moderately resistant cultivar 'Itadaki' (O. sativa L.) and the donor O. rufipogon. Two lines, IRSL 30 and IRSL 37, were selected as resistant. QTL analyses of the percentage of cracked kernels (PCK) in F4 individuals derived from "Itadaki/IRSL 30" and "Itadaki/IRSL 37" identified a major QTL, qCR (Cracking Resistance) 8-2, at the same position on chromosome 8 in both populations. 'IRSL 30' and 'IRSL 37' had a reduced PCK. These results show that qCR8-2 is likely to be an important QTL for kernel cracking resistance. Both lines had long awns, linked to qCR8-2, but the awnless line 'Chukei 19301' was also derived from "Itadaki/IRSL 37", so qCR8-2 is distinct from the gene for awn development. We consider that qCR8-2 will help in the breeding of new rice cultivars with high cracking resistance and in elucidating the physiological mechanism of kernel cracking.
ABSTRACT
OBJECTIVE: An experiment was conducted to assess the antioxidant contents and activities of colored rice grains and to evaluate their nutritive characteristics in terms of chemical composition and in situ ruminal degradation. METHODS: Ten cultivars of colored rice grains (Oryza sativa L.) collected from several areas of Japan were studied, and control rice without pigment, maize, barley, and wheat grains were used as control grains. Their chemical compositions, pigment, polyphenol contents, total antioxidant capacity (TAC), and degradation characteristics were determined. RESULTS: The starch contents of the colored rice grains were in the range of 73.5% to 79.6%, similar to that of the control rice grain. The black and red rice grains contained anthocyanin (maximum: 5,045.6 µg/g) and proanthocyanidin (maximum: 3,060.6 µg/g) at high concentrations as their principal pigments, respectively. There were significantly (p<0.05) positive relationships among the pigment contents, polyphenol content, and TAC values in the colored and control rice grains, indicating that the increase in pigment contents also contributed to the increased polyphenol content and TAC values in the colored rice grains. The dry matter and starch degradation characteristics, as represented by c (fractional degradation rate of slowly degradable fraction) and by the effective degradability, of the colored rice grains and the control rice grain were ranked as follows among commonly used grains: wheat>barley ≥rice>maize. The colored rice grains also included the most-digestible starch, since their potential degradable fraction and actual degradability at 48 h incubation were almost 100%. CONCLUSION: Colored rice grains have high potential to be used as antioxidant sources in addition to starch sources in ruminants.
ABSTRACT
A quantitative trait locus (QTL) analysis was conducted on grain appearance in Emi-no-kizuna, a rice cultivar that has superior and stable appearance of the brown rice grain and high tolerance to high temperature stress, by using F3 lines derived from Emi-no-kizuna and Tomohonami. The investigation was performed 2013 and 2015. In summer 2013 the air temperature was higher and the larger differences in grain appearance were observed. In the QTL analysis, a highly contributing locus, qGA8, was detected at the end of the short arm of chromosome 8. Because trends of reduced the occurrence of white immature kernel and increased the percentage of perfect grain were observed in Emi-no-kizuna genotype in both years, qGA8 is likely to be an important QTL that is dominant in the superior grain appearance of Emi-no-kizuna. Also, qGA8 was linked to a QTL associated with days to heading. Another QTL, qGA7, associated with grain appearance was detected on chromosome 7 in 2013. Because no negative correlation was found between the genotype of qGA8 and thousand grain weight, it should be possible to breed cultivars that possess Emi-no-kizuna genotype qGA8 without a decrease in thousand grain weight.
ABSTRACT
In this study, we investigated the genetic basis of seed shattering and dormancy in Hokuriku 193 and bred an NIL improved these traits. Analysis of an F3 population from Hokuriku 193 × Koshihikari revealed a general correspondence between seed shattering and genotypes at the qSH1 locus, suggesting a strong influence of this locus on the seed shattering in Hokuriku 193. An F2 population from [ms-bo] Nekken 2 × Hokuriku 193 was also analyzed to identify quantitative trait loci (QTLs) for seed dormancy as measured by germination rate in the first December and March after seed harvest. The results revealed a concurrence QTLs of on chromosomes 1, 3, and 6 (qSDo1, qSDo3, qSDo6). In particular, qSDo1 and qSDo6 were considered regions worthy of active modification because they were QTL regions that promoted seed dormancy when carrying Hokuriku 193 genome regions around. SSDo_NIL, a near isogenic line (NIL) derived from Hokuriku 193 by introgressing Nekken 2 alleles only at the qSH1 locus and qSDo1, did not shatter, and its germination rate was significantly higher than that of Hokuriku 193. Yield performance was similar between SSDo_NIL and Hokuriku 193, suggesting that improvement of seed shattering and dormancy does not affect yield.
ABSTRACT
To investigate the genetic background responsible for blast resistance in Oryza sativa L. 'Hokuriku 193', QTL analysis was conducted using the F3 lines from the cross [ms-bo] Nekken 2 × Hokuriku 193 that were artificially infected with rice blast fungus (Magnaporthe grisea). QTLs were detected on chromosomes 1, 4, 6 and 12 that correlated with greater blast resistance in the Hokuriku 193-type lines. Notably, the QTL on chromosome 12 had a major effect and localized to the same region where Pi20(t), a broad-spectrum blast resistance gene, is positioned, suggesting strongly that the blast resistance of Hokuriku 193 was controlled by Pi20(t). Also, QTL analysis of the lines found to have no Pi20(t) detected two QTLs on chromosome 4 (qBR4-1 and qBR4-2) and one QTL on chromosome 6 (qBR6), of which qBR4-2 and qBR6 correlated with higher percentages of resistant plants in the Hokuriku 193-type lines. The blast susceptibility of BR_NIL (a NIL of Hokuriku 193 from which Pi20(t) was eliminated) was greater than that of Hokuriku 193, suggesting that elimination of Pi20(t) may markedly increase blast susceptibility. The disease severity of BR_NIL was mild, which might be the effect of qBR4-2 and/or qBR6.
ABSTRACT
KEY MESSAGE: Breakage of the tight linkage between rice seed lipoxygenase - 3 and easy preharvest sprouting trait led to breeding of lines with few stale flavors after long storage and desirable preharvest sprouting resistance. Lipoxygenase-3 (LOX-3) is involved in the production of volatile constituents in stored rice, and the development of stale flavor is delayed in LOX-3 null rice. In the process of breeding new LOX-3-null lines with long storability, we found a close association between LOX-3 and preharvest sprouting resistance. To determine whether this relationship was due to the tight linkage of two genes or the pleiotropic effect of LOX-3, we performed marker-assisted selection using a BC3F3 population derived from crosses between LOX-3-present/preharvest sprouting-resistant lines and LOX-3-null/preharvest susceptible lines. In one individual, a recombination event occurred 13 kb downstream of LOX-3 (RM15750) and a significant quantitative trait locus, namely qPHS3, for easy preharvest sprouting trait (LOD = 10.4) was detected in an 842-kb region between RM15711 and RM15768. Using BC3F4 and BC3F5 populations, we succeeded in selecting LOX-3-absent and preharvest sprouting-resistant lines with only a 393-kb introgressed chromosome segment from the donor line for LOX-3-null at the LOX-3 locus on chromosome 3. This result indicated that the LOX-3 gene and the locus affecting preharvest sprouting are distinct. The selected line was named 'Hokuriku 244'. Sensory testing of rice grains with and without LOX-3 confirmed that stale flavor production in LOX-3-null rice during storage was lower than in normal LOX-3 rice. These results indicated that rice varieties with little stale flavor after long storage and preharvest sprouting resistance had been selected.
