Construction And Genetic Analysis Of Chromosome Segment Substitution Lines Using O.rufipogon As Donor

Common wild rice (O.rufipogon) is the progenitor of cultivated rice (O.sativa L.). which contains abundant genetic diversity. It is very important to broaden the narrowing genetic base in rice breeding by exploiting and utilizing favorable exotic alleles, which have been lost or weakened in cultivated rice during the course of domestication from wild rice. The wild rice is phenotypically less desirable in its overall appearance and performances. The favorable alleles are usually linked with the undesirable genes in wild germplasm. So it cannot be used as immediate material in breeding. With availability of high density molecular markers and saturated genetic linkage maps, it has become possible to find the valuable alleles in wild rice and breakdown the linkage drags efficiently. Certainly it also gives rather convenient to perform marker assisted selection (MAS) in transferring the target QTL during utilizing exotic germplasm.In this study, the common wild rice (IRGC-105491) from Malaysia as donor parent, the elite Chinese variety Zhenshan97 as recurrent parent, through crossing and successively backcrossing and selection by MAS, a set of primary chromosome segment substitution lines (CSSLs) including 96 individuals was constructed. During the construction of CSSLs two populations BC2F4 and BC3F3 were derived from the same parents cross. With the two populations we identified some agronomic traits QTLs. The main results as follows:1. CSSLs: the target segments in 96 individuals of primary CSSLs overlap the whole genome of rice with length of 363.8 Mb (about 1455cM). All of substitution segments add up to 1019.4 Mb, 2.8 times length of entire genome. The average length of substitution segments is 10.6 Mb (42.5cM) ranging from 28.7 Mb (114.8cM) to 0.15 Mb (0.6cM).2. A genetic linkage map consisting of 152 SSR markers, covering 1342.1 cM in whole genome, was constructed using the BC2F4 population, with an average interval of 8.8 cM. The linear order of markers in the map was in good agreement with that published previously. Among the marker used there were 19 markers segregated distortedly, distributed on chromosomes 1, 2, 3, 5, 6, 8 and 10. The SD direction is mostly skewing toward the O.rufipogon and heterozygous. Three severe segregation distortion regions were detected on chromosome 1, 6 and 8, and the peak SD markers were RM5407, RM19996 and RM22825.3. Composite interval mapping (CIM) and Inclusive composite interval mapping (ICIM) were used to identify QTLs in BC₂F₄ and BC₃F₃ populations respectively. In the two populations six traits were evaluated i.e. heading date, plant height. SPAD value, panicle number per plant, panicle length and thousand grains weight, 20 and 35 QTLs were detected in the two populations respectively, of which 7 QTLs were detected at about same position in the two populations. The grain shape traits such as grain length, grain width and ratio of length and width were also analyzed in BC2F4 population and 15 QTLs were identified. The QTLs analysis showed that 54% alleles from wild rice were favorable, indicating that the wild rice carry a tremendous wealth of potentially valuable alleles that could be utilized to improve rice variety.