Abstract
In rice, low threshability retains grains on the panicles especially in japonica rice ( O. sativa subsp. Japonica ) and high threshability makes it easier for harvesting in indica. The genetic mechanisms underlying moderate threshability in rice remain largely unclear. A set of reciprocal Backcross Inbred Lines BILs including 226 and 229 lines from indica rice ( O. sativa subsp. indica) and japonica rice (O. sativa subsp. japonica) backgrounds, respectively, and 262 recombinant inbred lines RILs developed from same cross between an indica, were adopted for testing threshability in two seasons. Percentages of dislodged grains were estimated at the maturity, harvesting and after sun drying. A total of 265 SNP markers developed based on sequencing and evenly distributed throughout the 12 chromosomes were used for genotyping assay. Inclusive composite interval mapping (ICIM) was used to dissect genomic regions and interactions affecting quantitative variation of threshability. A total of 13 QTLs were found to be conferring quantitative variations of threshability, which were distributed on all chromosomes. Two known major genes (QTLs) qSH1 and sh4 were also present. New additive QTLs, qThr1-a, qThr2, qThr3 qThr7, qThr8, qThr10, qThr11 and qThr12 were found as well. Twenty-four epistatics QTLs of which eight were common in both japonica and indica backgrounds were detected in two consecutive seasons. The overall threshability explained by all additive and interacting QTLs (R2) were 70% and 1 for indica, 15 and 8% for japonica and 17.4 and 10.6% for RIL backgrounds, respectively. Findings have preliminarily revealed a relatively complex mechanism underlying the quantitative variations of threshability in rice, which was controlled not only by major loci but also affected by epistasis and genetic background effects. Key words : epistasis, genetic background effect, quantitative variation, rice ( Oryza sativa L .), threshability
Highlights
Threshing is a technique of separating grains from the panicle
Analysis of threshability for Recombinant Inbred Lines (RILs) population indicated that degree of grain maturity had influence on threshability at P≤0.05 whereby repeatability was 95.5%
This was not the case for the Minghui 63’ (MH63)-IL and 02428-IL populations where threshing at maturity, harvesting and after sun-drying all had no significant influence on threshability at P≤0.05 with repeatability of 74% and 50% respectively
Summary
Threshing is a technique of separating grains from the panicle. The easy by which grains are removed from the panicle is called threshability. Threshability depends on the strength of spikelet attachment to the panicle (Kumar and Sharma, 1982). It varies depending on the variety, moisture content and the degree of maturity of the grain (FAO, 1994). Further studies have revealed that seed shattering is controlled by many quantitative trait loci (QTLs) widely distributed in rice genome (Eiguchi and Sano, 1990; Cai and Morishima 2000; Konishi et al, 2006; Li et al, 2006; Onishi et al, 2007; Zhang et al, 2009; Qin et al, 2010; He et al, 2011). Lin et al (2007) reported that selection for nonshattering trait during rice domestication occurred prior to O. sativa subsp. Indica, commonly referred to as indica rice and –O. sativa subsp. Three hypotheses have been reported regarding the direction of evolution of non-shattering trait: 1. Lin et al (2007) reported that selection for nonshattering trait during rice domestication occurred prior to O. sativa subsp. indica, commonly referred to as indica rice and –O. sativa subsp. japonica commonly referred to as Japonica rice differentiation
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