Abstract
ABSTRACT Grain shape in rice is a key determinant of grain appearance, yield and market value, and thus has been widely studied. Rice mutant lines with long-grain phenotypes were previously isolated from an M2 population derived from mutagenized mature pollen grains that were treated with gamma-ray irradiation for a cultivar Ma85. To understand the genetic basis underlying the long-grain trait, two mutant lines, JF171 and JF178, were crossed with the short-grain parents JF222 and Samba, generating three F2 populations. Molecular marker-based genetic analysis was employed to detect the major QTLs that affected grain length, grain width, length-to-width ratio and grain weight. Based on the data obtained for the three populations, a joint major QTL for grain length was mapped to a 4.7 Mb region between the SSR makers RM263 and RM318 on the long arm of chromosome 2. The results suggested that the two independent mutations contained in JF171 and JF178 are likely due to alterations in the same genetic region. Furthermore, we developed a BC2F2 population using JF178 and Samba and narrowed the region to 0.6 Mb. The results of the current study will be helpful to reveal the genetic basis of the above long-grain mutant lines. In general, our results provide solid genetic data to identify the unknown gene that affects grain length by map-based cloning and practice marker-assisted breeding for long-grain rice cultivars.
Highlights
Rice is one of the most important cereal crops in the world
JF171 and JF178 were initially selected as independent mutant lines with elongated grains from an M2 population created by applying mature pollen grains of Ma85 treated with gamma-ray irradiation to male-sterilized flowers of the same cultivar, Ma85 (Wang et al 2003)
The results showed that four major QTLs were detected on the lower portion of the long arm of chromosome 2, one locus each for grain length, grain width, grain thickness and 1000-grain weight (KGW) (Fig. 5g; Table 3)
Summary
Rice is one of the most important cereal crops in the world. Among the strategies proposed for improving rice yield and quality, development and application of superior cultivars is the most effective approach. Rice yield is a function of three major components: the number of panicles per plant, number of grains per panicle and grain weight. Grain weight is underlain by grain size and shape. Rice grain shape is measured as grain length, width, length-to-width ratio (L/W ratio) and thickness ( Huang et al 2013). In addition to contributing to grain yield, grain shape is an important quality trait of rice grain products (Unnevehr 1992; Juliano and Villareal 1993)
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