Abstract
Rice yield potential has been stagnant since the Green Revolution in the late 1960s, especially in tropical rice cultivars. We evaluated the effect of two major genes that regulate grain number, Gn1a/OsCKX2 and IPA1/WFP/OsSPL14, in elite indica cultivar backgrounds. The yield-positive Gn1a-type 3 and OsSPL14WFP alleles were introgressed respectively through marker-assisted selection (MAS). The grain numbers per panicle (GNPP) were compared between the recipient allele and the donor allele groups using segregating plants in BC3F2 and BC3F3 generations. There was no significant difference in GNPP between the two Gn1a alleles, suggesting that the Gn1a-type 3 allele was not effective in indica cultivars. However, the OsSPL14WFP allele dramatically increased GNPP by 10.6–59.3% in all four different backgrounds across cropping seasons and generations, indicating that this allele provides strong genetic gain to elite indica cultivars. Eventually, five high-yielding breeding lines were bred using the OsSPL14WFP allele by MAS with a conventional breeding approach that showed increased grain yield by 28.4–83.5% (7.87–12.89 t/ha) vis-à-vis the recipient cultivars and exhibited higher yield (~64.7%) than the top-yielding check cultivar, IRRI 156 (7.82 t/ha). We demonstrated a strong possibility to increase the genetic yield potential of indica rice varieties through allele mining and its application.
Highlights
Rice (Oryza sativa L.) is one of the most important cereal crops and it feeds more than half of the world’s population
The alleles of the Grain number 1a (Gn1a) gene were grouped into three types in the 12 recurrent parents based on the sequences of the Gn1a promoter region, which is directly involved in gene expression
We focused on evaluating the effect of the Gn1a-type 3 in the recipient cultivar backgrounds having the Gn1a-type 2 because the remaining four indica recipient cultivars already had the yield-positive Gn1a-type 3 allele
Summary
Rice (Oryza sativa L.) is one of the most important cereal crops and it feeds more than half of the world’s population. Grain size, grain filling ability, grain numbers per panicle (GNPP), and tiller number per plant, are directly associated with rice grain productivity. These traits are complex and quantitative in nature. The Grain number 1a (Gn1a) gene was isolated from high-yielding indica rice variety Habataki through QTL analysis with fine mapping analysis[13]. The WFP allele belongs to epigenetic alleles that show a heritable difference in gene expression that is caused by the degree of DNA methylation or chromatin status but not by DNA sequence variations[17] Another natural epigenetic allele, ipa1–2D, having tandem repeat sequences of the OsSPL14 promoter region was identified[18]. The IPA1 allele was found in other japonica varieties (Aikawa[116] and Ri2211)
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