Abstract
BackgroundIncreasing rice yield potential is a major objective in rice breeding programs, given the need for meeting the demands of population growth, especially in Asia. Genetic analysis using genomic information and high-yielding cultivars can facilitate understanding of the genetic mechanisms underlying rice yield potential. Chromosome segment substitution lines (CSSLs) are a powerful tool for the detection and precise mapping of quantitative trait loci (QTLs) that have both large and small effects. In addition, reciprocal CSSLs developed in both parental cultivar backgrounds may be appropriate for evaluating gene activity, as a single factor or in epistatic interactions.ResultsWe developed reciprocal CSSLs derived from a cross between Takanari (one of the most productive indica cultivars) and a leading japonica cultivar, Koshihikari; both the cultivars were developed in Japan. Forty-one CSSLs covered most of the Takanari genome in the Koshihikari background and 39 CSSLs covered the Koshihikari genome in the Takanari background. Using the reciprocal CSSLs, we conducted yield trials under canopy conditions in paddy fields. While no CSSLs significantly exceeded the recurrent parent cultivar in yield, genetic analysis detected 48 and 47 QTLs for yield and its components in the Koshihikari and Takanari backgrounds, respectively. A number of QTLs showed a trade-off, in which the allele with increased sink-size traits (spikelet number per panicle or per square meter) was associated with decreased ripening percentage or 1000-grain weight. These results indicate that increased sink size is not sufficient to increase rice yield in both backgrounds. In addition, most QTLs were detected in either one of the two genetic backgrounds, suggesting that these loci may be under epistatic control with other gene(s).ConclusionsWe demonstrated that the reciprocal CSSLs are a useful tool for understanding the genetic mechanisms underlying yield potential in the high-yielding rice cultivar Takanari. Our results suggest that sink-size QTLs in combination with QTLs for source strength or translocation capacity, as well as careful attention to epistatic interactions, are necessary for increasing rice yield. Thus, our findings provide a foundation for developing rice cultivars with higher yield potential in future breeding programs.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0295-2) contains supplementary material, which is available to authorized users.
Highlights
Increasing rice yield potential is a major objective in rice breeding programs, given the need for meeting the demands of population growth, especially in Asia
The yield potential of current highyielding inbred rice cultivars is 10 t · ha−1 as unhulled rice under favorable irrigated conditions [4]. This yield potential was first attained by IR8, the first modern high-yielding cultivar released by the International Rice Research Institute (IRRI) in the late 1960s
Chromosome segment substitution lines (CSSLs) are appropriate for detecting Quantitative trait locus (QTL) with both large and small effects, and reciprocal CSSLs confer the advantage of enabling evaluation of differences in allelic effects of QTLs in both genetic backgrounds
Summary
Increasing rice yield potential is a major objective in rice breeding programs, given the need for meeting the demands of population growth, especially in Asia. The predicted population growth in Asia will require a 60–70% increase in rice production by 2050, In the tropics, the yield potential of current highyielding inbred rice cultivars is 10 t · ha−1 as unhulled rice under favorable irrigated conditions [4]. This yield potential was first attained by IR8, the first modern high-yielding cultivar released by the International Rice Research Institute (IRRI) in the late 1960s. The release of IR8 and subsequent high-yielding cultivars helped to more than double rice production over the past half century. Recent trends in yield in tropical environments indicate that yield potential has stagnated since the release of IR8 [6]
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