Abstract
Background: Grain shape affects not only rice yield but is also an important element in quality of appearance. However, the mechanism for inheritance of grain shape is unclear.
Results: A rice chromosome segment substitution line Z1392, which harbors three substitution segments and produces grains of increased length, was identified. The three chromosome segments were located on chromosomes 1, 5, and 6, and the average length of the substitution segment was 4.29 Mb. Cytological analysis indicates that the predominant cause of increased grain length in Z1392 could be cell expansion in the glumes. 18 quantitative trait loci (QTLs) for important agronomic traits were identified. The inheritance of grain length in Z1392 was controlled by two major QTLs, qGL-5 and qGL-6 . Finally, the qGL-6 was narrowed to a 1.26 Mb region on chromosome 6, and OsARF19 may be the candidate gene of qGL-6 . Based on QTL mapping, three single-segment substitution lines (S1, S2, and S3) and two double-segment substitution lines (D1 and D2) were selected, and the mapping accuracy for qGL-5 and qGL-6 was further verified using the three single-segment substitution lines. Analysis of QTL additive and epistatic effects revealed that the additive effect of alleles qGL5 and qGL6 from ‘Xihui 18’ was estimated to increase grain length of Z1392 by 0.22 and 0.15 mm, respectively. In addition, a positive epistatic interaction between qGL-5 and qGL-6 was detected, which indicates that the pyramiding of qGL-5 and qGL-6 for grain length produces a novel genotype with longer grains.
Conclusions: Inheritance of grain length in the triple-segment substitution line Z1392 is controlled by two major QTLs, qGL-5 and qGL-6 , qGL-6 was narrowed to a 1.26 Mb region on chromosome 6, OsARF19 may be the candidate gene of qGL-6 . And a positive epistatic interaction between qGL-5 and qGL-6 results in longer grains. The present results could be used to facilitate cloning of the qGL-5 and qGL-6 genes and contribute to improvement in grain yield in rice.
QTL analysis based on a long-grain CSSL-Z1392 and SSSLs and fine mapping of qGL6
