Kiyoyuki Miura

A single nucleotide polymorphism in the alternative oxidase gene among rice varieties differing in low temperature tolerance

Alternative oxidase (AOX) is encoded in a multigene family, and multiple isoforms have been observed in various plant species. We found for the first time an allelic variation in the same AOX locus. On SDS–gel blots of callus protein of rice (Oryza sativa L.), varieties without the QTL for low temperature tolerance showed a 32‐kDa AOX band, whereas those with the QTL showed a 34‐kDa band. The variation was attributed to the substitution of Lys71 for Asn71 caused by a single nucleotide polymorphism between alleles of OsAOX1a, and was tightly linked to the presence of the QTL.

Variation in heading date conceals quantitative trait loci for other traits of importance in breeding selection of rice

To identify quantitative trait loci (QTLs) associated with the primary target traits for selection in practical rice breeding programs, backcross inbred lines (BILs) derived from crosses between temperate japonica rice cultivars Nipponbare and Koshihikari were evaluated for 50 agronomic traits at six experimental fields located throughout Japan. Thirty-three of the 50 traits were significantly correlated with heading date. Using a linkage map including 647 single-nucleotide polymorphisms (SNPs), a total of 122 QTLs for 38 traits were mapped on all rice chromosomes except chromosomes 5 and 9. Fifty-eight of the 122 QTLs were detected near the heading date QTLs Hd16 and Hd17 and the remaining 64 QTLs were found in other chromosome regions. QTL analysis of 51 BILs having homozygous for the Koshihikari chromosome segments around Hd16 and Hd17 allowed us to detect 40 QTLs associated with 27 traits; 23 of these QTLs had not been detected in the original analysis. Among the 97 QTLs for the 30 traits measured in multiple environments, the genotype-by-environment interaction was significant for 44 QTLs and not significant for 53 QTLs. These results led us to propose a new selection strategy to improve agronomic performance in temperate japonica rice cultivars.

Introduction of the Long-Coleoptile Trait to Improve the Establishment of Direct-Seeded Rice in Submerged Fields in Cool Climates

Abstract Introduction of the long-coleoptile trait in European varieties into Japanese elite varieties may improve seedling establishment and yield stability of the rice in the direct-seeding cultivation in cool climates. Some European varieties have long coleoptiles but they also have undesirable traits such as low yielding ability and bad grain appearance, which makes it difficult to improve coleoptile length in a rice breeding programs in Japan. To overcome this difficulty, we introduced the long-coleoptile trait of Arroz da Terra (Portuguese variety with long coleoptile) into Kitaibuki (Japanese elite variety for direct seeding cultivation) by backcrossing. Furthermore, we confirmed the effectiveness of introducing the long-coleoptile trait for the selection of lines with stable seedling establishment. The coleoptile length of Satsukei00019, a near isogenic line of Kitaibuki for the long-coleoptile trait, was about twice as long as that of Kitaibuki. The seedling establishment rate of Satsukei00019 was about 20% higher than that of Kitaibuki in the direct seeding cultivation in submerged fields. Eating quality, heading date and yield of Satsukei00019 were similar to those of Kitaibuki but 1,000 grain weight of Satsukei 00019 was larger. Therefore, the efficacy of backcross breeding to introduce the long-coleoptile trait of European varieties into Japanese elite varieties was confirmed. From these results, we concluded that the selection based on a longer coleoptile length improved seedling establishment in submerged fields in cool climates which can contribute to stable production of direct seeded rice.

Quantitative trait loci analysis of blast resistance in Oryza sativa L. ‘Hokuriku 193’

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.

The Effect of High-Temperature Stress Applied to the Root on Grain Quality of Rice

Abstract We verified the effect of high-temperature stress applied to the root on the occurrence of white immature kernels (WIKs) in order to breed rice (Oryza sativa L.) cultivars tolerant to the high temperature during the ripening period. The plants were grown in control and warmed pools after the heading date. The WIK percentages in the warmed pool were higher than those in the control pool. This suggests that high-temperature stress applied to the root increases the occurrence of WIKs. On the other hand, the WIK percentages correlated positively and significantly with the 1000 kernel weight and kernel width, suggesting that rice cultivars with high-temperature tolerance might have a smaller and/or thinner grain.

Improvement of seed shattering and dormancy in Oryza sativa L. ‘Hokuriku 193’ based on genetic information

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.

Quantitative trait loci analysis of grain appearance in Oryza sativa L. 'Emi-no-kizuna'

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.

A new rice variety “Nagomi-Risotto” suitable for Italian rice dish Risotto with extra-large grain

米穀安定供給確保支援機構の調査(2017)によると, 精米消費量の約 3割が家庭外,すなわち外食・中食で消 費されている.特に外食では,白飯以外の様々な料理で 提供される場合も多く,実需者からは,それぞれの料理 に合わせた業務用米への要望が高まっている.従来,業 務用米は食味の異なる複数品種のブレンド等で様々な用 途に対応していたが,主食用品種の食味の画一化が進ん だこともあり,最近は料理に合わせた品種が育成されて いる.例えば,表面の粘りは少なく硬いが,米飯全体は 柔らかく,日本人の嗜好に合ったカレー向き品種の「華 麗舞」(重宗ら 2011),粘りが少なく寿司に向く「笑みの 絆」(笹原 2012),「東北 194号(愛称「ささ結」など)」 (永野ら 2017)など,日本の米料理に適した品種が育成 されている. イタリアの米料理であるリゾットは,カレー,寿司の ように国内で日常的に食されるものではないが,イタリ ア料理の普及に伴い,各地の専門店で提供されている. リゾットは,バターなどの油脂で米を炒めた後に,熱し たブロード(ブイヨン)を加えながらアルデンテ(歯ご