| Because of the increasing population and decreasing farmland, it is a realistic choice to ensure food security by improving the yield per unit in China. Research results showed that the contribution of varieties to yield exceed one third of total factors. In the past forty years, rice variety was renewed quickly and yield increased exponentially, which were resulted from the discovery and efficient utilization of special germplasm. R1126is a unique germplasm which was created through distant composite crossing in Hunan Hybrid Rice Research Center in recent years. Spikelets per panicle of R1126exceed300, individual main panicles have more than500spikelets, and average seed setting rate exceeds85%. It has quick filling rate, good grain quality, thick culm and wide leaves. Rl126is an ideal material for the rice breeding, favorable genes mining and theoretical research. In this paper, the characteristics of R1126were studied, and the results were used for guiding breeding practices. In the process of improving R1126, Near-isogenic lines of the big grain gene GS2was discovered, and the GS2gene was fine mapped. In addition, the QTL responsible for agronomic traits in Rl126were analyzed and mapped using the results of whole genome sequencing and primary mapping population (F2population, Huanghuazhan/R1126). The main results are as follows: 1. R1126has big panicle and many grains per panicle, strong lodging resistance, quick filling rate per panicle, high ability of anti-premature decrepitude of the canopy leaves (a late-Stage vigor new materials for rice breeding). However, it also has weak tillering, thick culm and wide leaves. The combinations or improvement of R1126should follow the principles that can improve the plant type, increase tillering (the spikelets per panicle maybe down) and1000-grain weight, keep the R1126leaves ability of anti-premature decrepitude.2.24important functional genes of R1126were analyzed. Among them,6genes relate to growth period,2genes control spikelets number per panicle,5genes related to1000-grain weight,3genes control seed shattering and8genes control plant type. The17genes were preliminarily confirmed, and the7genes need to be further studied. For example, the coding sequence of GIF1gene which relate to filling rate exists difference between Rl126and Nipponbare. Whether the strong grouting ability of R1126related to the variation of the GIF1gene need further study.3. By composite interval mapping analysis,21QTL that control plant type were detected, which distribute in7regions on3,4,6,8,9and12chromosome;12QTL that control panicle traits were detected, which distribute in6locus on3,4,8,10and12chromosome. RM303-RM6748interval on chromosome4and RM80-RM447interval on chromosome8 are two major and multi-effect lotus, all QTL derived from R1126have synergistic effect:the locus on chromosome4is responsible for flag leaf width,2nd top leaf width,3rd top leaf width,3rd top leaf weight, stem diameter,2nd top section length, stem weight, spikelets per panicle and secondary branch number, which has a contribution rate of23.8%to flag leaf width,31.56%to2nd top leaf width and19.25%to3rd top leaf weight, more than10%to2nd top section length, stem weight and secondary branch number; The regions on chromosome8is responsible for flag leaf width,2nd top leaf length,2nd top leaf width,2nd top leaf weight,3rd top leaf length,3rd top leaf weight, stem diameter, stem weight, spikelets per panicle, panicle length, first panicle branch number and secondary branch number, which has a contribution rate of36.41%to2nd top leaf weight,36.53%to stem diameter49.89%to panicle length,56.67%to first panicle branch number,10%-20%to2nd top leaf length,2nd top leaf width,3top leaf length,3top leaf weight, and secondary branch number.4. Higher fertility levels, the storage capacity of Y58S/R642-2and P88S/R642-2(the big grain improved line of R1126) exceeded15t/hm2in Hainan, and the yield of Y58S/R642-2and P88S/R642-2increased10%over the Y Liangyoul (CK). A new morphological model of the middle-lower Yangtze River valley for super high-yielding was proposed, the core technology are big grain, heavy panicle and anti-premature decrepitude of the canopy leaves:the plant type follow the morphological model which was proposed by academician Yuan Longping; enhance1000-grain weight (30-35g), harmony among panicles/hm2, spikelets/panicle and1000-grain weight, optimize and maximize the storage capacity per plant and population; anti-premature decrepitude of the canopy leaves, grain nonshattering and resistible to sprouting, prolong the duration of the accumulation of dry weight in grains.5. Big grain gene GS2can increase the grain length (3mm) and grain width (0.3mm), and has dominance effect. The GS2gene was fine mapped in33.2kb interval on chromosome2(between InDel markers GL2-35-1and GL2-12). According the result of fine mapping, gene annotation and semi-quantitative analysis, LOC_Os02g47280was considered as the most likely candidate gene of GS2. The result of cytological observation showed cell expansion maybe the main reason for the longer and wider grain. Dominant big-grain gene GS2generally increase the grain length (3mm) and1000-grain weight (18g). The results offer the key gene resource of big grain for new morphological model, which will promote the new varieties breeding of super rice with big grain. |
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