Identification of an excellent rice chromosome segment substitution line Z746 and QTL mapping and verification of important agronomic traits.

The important agronomic traits, such as grain type, plant height, and panicle composition, are closely related to rice yield, and their gene inheritance is complex. Chromosome segment substitution lines (CSSLs) are useful materials for studying these complex traits. An excellent CSSL, Z746, containing seven substitution segments and with an average substitution length of 3.99 Mb, was identified from Nipponbare as a recipient and 'Xihui 18' as a donor parent. There were significant differences in plant height, panicle composition and grain size between Z746 and Nipponbare. Furthermore, a total of 36 quantitative trait loci (QTL) were detected on chromosomes 2, 3, 4, 6, and 11 in the secondary F₂ population constructed by hybridization between Nipponbare and Z746. Five of them may be alleles of the cloned genes, such as qPH3-1, and eight can be detected by multiple times, indicating that these were genetically stable major QTLs. The grain length in Z746 was mainly controlled by four QTLs (qGL3, qGL4, qGL2, and qGL6), and the phenotypic variation of qGL3 and qGL4 for grain length was 60.28% and 27.47%, respectively. Plant height was controlled by five QTLs, panicle length by four QTLs, grain number per panicle by two QTLs, and the 1000-grain weight by two QTLs. Eight single segment substitution lines (SSSLs) were developed in F₃ population by molecular marker-assisted selection (MAS), and relevant QTLs verification was conducted in F₄. Finally, 24 QTLs were detected by 8 SSSLs and the repeat detection rate was 66.7%, indicating that these QTLs were genetically stable. These results provide a good foundation for further research on genetic mechanisms of the target QTLs and molecular design breeding. [ABSTRACT FROM AUTHOR]