Development Of Contiguous Introgression Lines And QTLs Analysis Of The Yield In Rice

Yield as a major breeding objective in rice, is directly influenced by the yield-component traits including the number of productive tillers per plant, grains per panicle and 1000-grain weight. To elucidate genetic basis of the yield, to fine map or isolate genes (or QTL) related with the yield traits, and to breed new varieties of rice, we developed a set of novel population with introgression chromosome segments of japonica variety Nipponbare in the genetic background of indica variety zhenshan97B through backcross program and molecular marker-aided selection (MAS), in which each of the lines contains a single chromosome segment derived from japonica variety, and together all lines with those mutual overlapping introgression chromosome segments provide complete coverage of the japonica genome. Using the contiguous introgression lines, we enable to assess systematically the genic effect of different alleles in the same genetic background and anatomize the gene effect on yield, moreover to better understand the genetic basis of yield traits and to utilize intersubspecific heterosis between indica and japonica.In this studying program, we firstly obtained a BC₄ population consisting of about 500 plants via backcrossing introgression scheme, in which Nipponbare used as donor parents and Zhenshan97B as recurrent parent. One hundred and eight polymorphic SSR markers were assayed for the population, and graphical genotyping of each BC₄ plant were performed using the software GGT. According to the graphical genotypes, 88 individual plants from the BC₄ population were selected to construct basal contiguous introgression lines (CILs). In order to eliminate some redundant chromosome segments and to improve the genome recovery of the genetic background of Zhenshan97B, one more backcross to advance the BC₅ generation and MAS selection procedure were carried. As a result, a CILs population consisting of 124 plants was developed with the introgression segments from japonica rice that did perfectly cover the whole japonica genome, except that two regions on the chromosome 2 and 6. In order to preserve the IL (introgression lines) population immortally, the BC₅F₁ generation was self-pollinated and then the target homozygous exotic chromosome segments were selected from the BC₅F₂ population. Meanwhile, we had to analyze more than 200 BC₄F₁ or BC₃F₂ plants to retrieve the absent segments of the chromosomes 2 and 6. Consequently, a set of CILs population consisting of 145 plants are successfully developed, in which the average proportion ofrecurrent parent genome is 98.1% with the average length of introgression segments of 19.7 cM.Secondly, we investigated the genetic effects of each introgression segment on the yield and its component traits using the 88 base introgression lines by three ways of the experimental cross-designs that produced ILs self-pollinated, ILs X Zhenshan97B and ILs X Minhui63. Field trails of the 88 ILs and its hybrids were conducted in a randomized complete block design in the rice growing seasons in 2003 and in 2004, respectively. The traits including yield per plant, numbers of tillers per plant, numbers of grains per panicle and 1000-grain weight were evaluated. The genetic effect of introgression segments was analyzed through one-way of variance analysis (ANOVA) and least significant difference (LSD) test. In the trial of ILs self-pollinated, we found 30 ILs each containing one or two putative QTLs associated with yield per plant, 31 ILs with putative QTLs associated with 1000-grain weight, 24 ILs carrying putative QTLs associated with numbers of tillers per plant and 36 IL with putative QTLs associated with numbers of grains per panicle. In the trial of ILs X Zhenshan97B and ILsXMinhui63 with Zhenshan97B and Zhenshan97B X Minhui63 as a check respectively, 31 loci or segments were detected with significant heterotic effect on yield per plant, 9 loci detected for numbers of tillers per plant, 21 loci for numbers of grains per panicle and 21 loci for 1000-grain weight.Finally, we also discusse the potential utilization of the set of contiguous lines developed in this study for further QTL mapping, gene fine mapping and isolation, and variety improvement.