Identification for Heat Tolerance in Backcross Recombinant Lines and Screening of Backcross Introgression Lines with Heat Tolerance at Milky Stage in Rice

The present study aimed at breeding new rice germplasms with similar genome but significantly differed in heat tolerance during the grain filling stage.A total of 791 BC1F8 backcross recombinant lines,derived from the cross of Xieqingzao B /N22 //Xieqingzao B,were used as materials.Each rice line was separated evenly into two groups,and the heat tolerance of all rice lines were evaluated at natural high temperature in fields.The rice lines with heat tolerant index higher than 90% or lower than 40% were selected to compare the phenotypic characters and further identify heat tolerance at the early milky stage in a phytotron.Rice lines with similar phenotypic characters but significantly differed in heat tolerance at the milky stage were analyzed by 887 simple sequence repeat markers that were evenly distributed on the 12 rice chromosomes.In the result,12(6 pairs) rice lines with similar phenotypic characters but significantly differed in heat tolerance at the milky stage were obtained.Molecular marker analysis indicated that the genomic polymorphism between 703T and 704S was the smallest in the 6 pairs of rice lines,with only 16 polymorphic sites,including 22 different alleles.The application of these two backcross introgression rice lines for future study on the mechanisms of heat tolerance in rice at the milky stage will be theoretically beneficial in reducing the interference caused by genetic differences from experimental materials.

Dissecting Genetic Basis of Deep Rooting in Dongxiang Wild Rice

Deep rooting is an important trait in rice drought resistance.Genetic resources of deep-rooting varieties are valuable in breeding of water-saving and drought-resistant rice.In the present study,234BC2F7 backcross introgression lines were derived from a cross of Dongye 80(an accession of Dongxiang wild rice as the donor parent)and R974(an indica restorer line as the recurrent parent).A genetic linkage map containing 1977 bin markers was constructed by ddRADSeq for QTL analysis.Thirty-one QTLs for four root traits(the number of deep roots,the number of shallow roots,the total number of deep roots and the ratio of deep roots)were assessed on six rice chromosomes in two environments(2020 Shanghai and 2021 Hainan).Two of the QTLs,qDR5.1 and qTR5.2,were located on chromosome 5 in a 70-kb interval.They were detected in both environments.qDR5.1 explained 13.35%of the phenotypic variance in 2020 Shanghai and 12.01%of the phenotypic variance in 2021 Hainan.qTR5.2 accounted for 10.88%and 10.93%of the phenotypic variance,respectively.One QTL(qRDR2.2)for the ratio of deep roots was detected on chromosome 2 in a 210-kb interval and accounted for 6.72%of the phenotypic variance in 2020.The positive effects of these three QTLs were all from Dongxiang wild rice.Furthermore,nine and four putative candidate genes were identified in qRDR2.2 and qDR5.1/qTR5.2,respectively.These findings added to our knowledge of the genetic control of root traits in rice.In addition,this study will facilitate the future isolation of candidate genes of the deep-rooting trait and the utilization of Dongxiang wild rice in the improvement of rice drought resistance.