The Characterization Of Introgression Lines With Background Of An Elite Restorer Line In Rice

Asian cultivated rice (Oryza sativa L.) mainly includes Indica and Japonica subspecies and the F₁ hybrid between the two subspecies has great potential heterosis, which can be exploited to increase rice yield. Rice yield is a main breeding goal that is affected by yield components such as panicle weight, the number of branches, seed setting rate, spikelets per panicle, 1000-grain weight and productive tillers. A set of introgression line (IL) population, each of lines containing a single or few chromosomal introgression segments with the indica background, and all the segments overlapped covering the whole genome of japonica, has been constructed by backcrossing and marker-aided selection with Japonica variety Nipponbare as donor parent and Indica variety 9311 as recurrent parent. We analyzed genetic effect and action pattern of introgression segments of the Japonica in the Indica background using the IL population as well as two set of testcross populations (IL/ 9311 and Yuetai A/ IL). The objectives of this study are to dissect the genetic effect of introgressed Japonica alleles and provide theoretical and applied basis for utilization of beneficial genes from the two subspecies. The main results are as follows:1. By analyzing the genotype of 127 intergression lines using 165 polymorphic SSR markers we found that the genomic proportion of 9311 was 96.3% where as the average proportions of homozygous and heterozygous donor segments were 3.3% and 0.4% respectively. These results showed that the target chromosomal segments in this introgression lines covered the whole genome of rice.2. Twelve important agronomic traits were evaluated and all showed nearly normal distributions in the three sets of population, the introgression lines (IL), IL / 9311 backcross population and Yuetai A/IL testcross population. Yield per plant and yield-related traits, such as panicle length, panicle weigh,spikelet per panicle, seed setting rate, the number of secondary branches, 1000-grain weight, theoretical yield per plant, productive tillers per plant, showed transgressive segregations in the three populations. Yield per plant was significantly related to productive tillers per plant, plant height, panicle length, panicle weigh, spikelet per panicle, the number of secondary branch and theoretical yield per plant in each population.3. Fifty introgression segments containing 95 QTLs for 12 important agronomic traits were identified in the IL population, and 38 introgression segments haboring 66 QTLs affecting these traits identified in the backcross population (IL/9311), whereas, 30 introgression regions containing 76 QTLs affecting these traits identified in the testcross hybrid population (Yuetai A/IL).4. Among the QTLs detected in each population, 75 QTLs were identified in the IL population only, neither detected in the backcross population nor in the testcross population. Twenty QTLs were identified in both the IL and the backcross population, of which 8 QTLs constantly detected among the 3 sets of population, indicating that the 21 QTLs had additive, dominant and probably epistatic effects. Thirty-eight QTLs were identified only in the backcross population, and 7 QTLs were only identified in both the backcross population and testcross population, suggesting that these QTL were mainly dominant. Meanwhile, 4 QTLs were only identified in both the IL and the backcross population, not detected in the testcross population, 57 QTLs were only revealed in testcross population, suggesting there were epistatic interactions between the introgression segments (QTLs) and otherwise loci in the background of Yuetai A/9311.5. Thirty-eight multi-effective QTL regions, each affecting 3 or more traits were also detected in the 3 sets of population. For example, a region near RM302 on chromosome 1 simultaneously controlled panicle length, panicle weight, secondary branches and spikelets per panicle, 1000-grain-weight and plant weight were found. The region nearby RM305 on chromosome 5 were simultaneously found affecting productive tillers per plant, panicle length, panicle weight, secondary branches of main panicle, seed setting rate, theoretical production per plant. A region near RM527 on chromosome 6 simultaneously affecting yield per plant, plant height, heading date, panicle length, panicle weight, the number of second branches, spikelets per panicle, theoretical yield per plant were found in the testcross population, and this QTL region controlled heading date, plant height were also identified in the backcross population. It revealed that these QTL mainly have dominant effects, and probably have epistatic effects. Those multi-effective QTL regions might be the genetic basis of significant correlation of the evaluated traits.