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Detection of QTLs for cold tolerance of rice cultivar ‘Kuchum’ and effect of QTL pyramiding

Endo, Takashi, Chiba, Bunya, Wagatsuma, Kensuke, Saeki, Kenichi, Ando, Tsuyu, Shomura, Ayahiko, Mizubayashi, Tatsumi, Ueda, Tadamasa, Yamamoto, Toshio, Nishio, Takeshi
Theoretical and applied genetics 2016 v.129 no.3 pp. 631-640
Oryza sativa, agronomic traits, alleles, chromosomes, cold tolerance, cultivars, genetic background, genetic markers, homozygosity, isogenic lines, pollen, quantitative trait loci, rice, summer, temperature, Japan
KEY MESSAGE : A QTL for cold tolerance at the booting stage of rice cultivar ‘Kuchum’ was detected and delimited into a 1.36 Mb region, and a cold-tolerant line was developed by QTL pyramiding. Low temperature in summer causes pollen sterility in rice, resulting in a serious loss of yield. The second most widely grown rice cultivar in Japan, ‘Hitomebore’, has been developed as a cultivar highly tolerant to low temperature at the booting stage. However, even ‘Hitomebore’ exhibits sterility at a temperature lower than 18.5 °C. Further improvement of cold tolerance of rice is required. In the present study, QTLs for cold tolerance in a Bhutanese rice variety, ‘Kuchum’, were analyzed using backcrossed progenies and a major QTL, named qCT-4, was detected on chromosome 4. Evaluating cold tolerance of seven types of near isogenic lines having ‘Kuchum’ alleles around qCT-4 with a ‘Hitomebore’ genetic background, qCT-4 was delimited to a region of ca. 1.36 Mb between DNA markers 9_1 and 10_13. Homozygous ‘Kuchum’ alleles at qCT-4 showed an effect of increasing seed fertility by ca. 10 % under cold-water treatment. Near isogenic lines of ‘Hitomebore’ having ‘Silewah’ alleles of Ctb1 and Ctb2 and a ‘Hokkai PL9’ allele of qCTB8 did not exhibit higher cold tolerance than that of ‘Hitomebore’. On the other hand, a qLTB3 allele derived from a Chinese cultivar ‘Lijiangxintuanheigu’ increased cold tolerance of ‘Hitomebore’, and pyramiding of the qCT-4 allele and the qLTB3 allele further increased seed fertility under cold-water treatment. Since NILs of ‘Hitomebore’ with the ‘Kuchum’ allele of qCT-4 were highly similar to ‘Hitomebore’ in other agronomic traits, the qCT-4 allele is considered to be useful for developing a cold-tolerant cultivar.