The pubescence of the leaf blade surface is an important agronomic characteristic for rice morphology and significantly influences rice growth as well as physiological characteristics. This characteristic was analyzed in F 1 and F 2 plants derived by crossing cultivar 75-1-127 with the indica cultivar Minghui 63, as well as the glabrous cultivar Lemont and indica cultivar 9311. Results indicated that the pubescence of the leaf blade surface was a dominant trait and controlled by a single gene. The GL6 gene was primarily mapped on rice chromosome 6 with recessive F 2 population derived from 75-1-127/Minghui 63 by combining bulked segregation analysis and recessive class analysis using the Mapmaker3.0/MapDraw software. The genetic distances between the simple sequence repeat markers RM20491 and RM20547 were 7.2 and 2.2 cM, respectively. The GL6 gene was fine mapped in the interval between InDel-106 and InDel-115 at genetic distances of 0.3 and 0.1 cM, respectively. The large, recessive F 2 population was derived from 75-1-127/Minghui 63. A high-resolution genetic and physical map of GL6 was constructed. Derived from the map-based sequences published by the International Rice Genome Sequencing Project, the GL6 gene was localized at an interval of 79 (japonica) and 116.82 kb (9311) bracketed by InDel-106 and InDel-115 within the BAC accession numbers AP008403 and AP005760. Seven annotated genes (japonica) and eight annotated genes (9311) were present. The basis was further set for GL6 cloning and function analysis.

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The fragrant rice breeding has become an important direction for hybrid rice breeding program. The selection and utilization of parent materials with ideal plant type, fine grain quality, strong resistance and other excellent agronomic characteristics with strong fragrance, especially the utilization and cultivation of the fragrant rice restorer lines, is of great significance to further promote the fragrant hybrid rice breeding. Taiguoxiaoxiangzhan is a restorer line with excellent grain quality, strong resistance and fragrance, which has been widely used in fragrant rice breeding in China. In order to trace the fragrance in Taiguoxiaoxiangzhan, we identified the type of the fragrance gene in Taiguoxiaoxiangzhan was badh2-E7 which has an 8 bp deletion and three single nucleotide polymorphisms (SNPs) in exon 7, and this gene is a non-functional badh2 allele and that the functional Badh2 allele encoding betaine aldehyde dehydrogenase (BADH2) could render rice non-fragrant. Furthermore, we found that the Taiguoxiaoxiangzhan increased 2-acetyl-1-pyrroline (2-AP) content (0.108 mg/kg) compared with the non-fragrant rice varieties of Nipponbare and 9311 (<0.01 mg/kg) by the GC-MS method. We also proved that FMbadh2-E7 and InDel-E7, two molecular markers reported earlier, can be applied in different genotypes, including Badh2/Badh2 (non-fragrance homozygote), Badh2/bahd2 (non-fragrance heterozygote) and badh2/badh2 (fragrance homozygote). In addition, based on sequence divergence amongst the functional Badh2 and null badh2-E7 allele, we developed two functional markers, FMbadh2-E7A and FMbadh2-E7B, which can be easily used to distinguish non-fragrant from fragrant rice. Genetic analysis shows that the segregation of Badh2/Badh2, Badh2/badh2 and badh2/badh2 in the F2 population derived from crosses between Taiguoxiaoxiangzhan and different restorer lines fitted a theoretical ratio of 1:2:1, indicating that the fragrance of Taiguoxiaoxiangzhan is controlled by a single nuclear recessive gene (bahd2). In this study, the identification and genetic analysis of the fragrance gene in Taiguoxiaoxiangzhan and the development of functional markers for fragrance have been studied, which provides a theoretical foundation for the further breeding of fragrant hybrid rice with excellent quality, high yield and strong resistance by molecular marker-assisted selection technology.