Abstract

Rice (Oryza sativa L.) kernel fissuring causes breakage during milling and thereby decreases the value of rice. This study employed molecular gene-tagging methods to fine map a fissure resistance (FR) locus in ‘Cybonnet’, a semidwarf tropical japonica cultivar, as well as to transfer this trait to rice genotypes of non-semidwarf stature that are better adapted to some rice production systems. Three quantitative trait loci (QTLs) for FR were previously reported, with the FR locus linked with the semidwarf sd-1 locus on chromosome 1 having the strongest effect. For fine mapping, F₂ progeny were produced from a cross between US breeding line RU1201108, having non-semidwarf height (Sd-1/Sd-1) and poor milling quality, and Cybonnet (sd-1/sd-1), having semidwarf height and containing multiple FR loci. Simple sequence repeat (SSR) markers were used to select F₂ plants that both retained at least one copy of the Sd-1 allele and showed evidence of genetic recombination in the region of chromosome 1 known to contain Sd-1 and qFIS1-2, a QTL for FR. Progeny from three F₂ individuals with desirable recombination at the qFIS1-2 were phenotyped for kernel FR. Marker-trait linkages observed in the three populations indicated that the qFIS1-2 locus resides on chromosome 1 distal to RM1068 at 38.44 Mb, but anterior to RM3482 at 39.72 Mb, placing it ∼6 to 10 cM distal to sd-1 on chromosome 1. The recombination documented in this study verifies that the previously identified qFIS1-2 is not pleiotropic with nor reliant on sd-1 and can be recombined with Sd-1 to increase the FR of non-semidwarf rice cultivars.

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