| Xiushui09, a high-yielding semi-dwarf japonica rice variety from China and IR2061, an drought tolerant indica breeding line from Philippine were used to construct two sets of BC2F6 reciprocal introgression lines ( XS-ILs and IR-ILs) and a set of F7 recombinant inbred lines (RIL), to detect genetic constitution of the reciprocal introgression lines and the main-effect QTLs related with the important agronomic traits including salinity tolerance (ST), heat tolerance (HT), cold tolerance (CT), drought tolerance (DT) and yield traits, and study the genetic background (GB) and environmental effects on QTL detection governing these important agronomic traits in rice.1. The genetic constitution analysis of the reciprocal introgression lines and the dissection of sterility due to subspecific differentiation within rice.The two sets of reciprocal introgression lines were used to analyze the principle of the frequency, number and size of introgression. The results showed the average introgression frequency of japonica genome into indica genetic background in IR-ILs was higher than XS-ILs. Introgression at individual chromosomes and genomic regions did not appear to be random in the reciprocal ILs. The most striking difference between the reciprocal IL sets was detected at most markers on chromosome 9 where introgression of all segments in the both introgression lines was very low and the introgression showing opposite directions in the reciprocal IL sets was detected on chromosomes 2, 7 and 11. Introgression along individual chromosomes was also not random. The average size of introgressed segments in the distal regions was shorter than those in the interstitial chromosomal regions, indicating that recombination appeared to have occurred more frequently near ends of individual chromosomes. The reason of difference of introgression frequency between XS-ILs and IR-ILs was analyzed depending on fertility rate as an index. The results showed that the indica genome have a better ability to adopt the effect of extrinsic introgression than japonica rice, suggesting that the japonica gene pool may tend to have a higher genetic load than the indica gene pool.2. Identification of salt-tolerant QTLs with strong genetic background effect using two sets of reciprocal introgression lines in riceA total of 26 QTLs with 13 each from the two sets of the reciprocal introgression lines separately were identified and mapped on all chromosomes except 6 and 8. Among 26 QTLs affecting ST related traits, only 4 (15.4%) QTLs (2 QSst3 for SST; 2 QDss5 for DSS) were commonly detected in the reciprocal backgrounds, each having the opposite direction of gene effect on the same trait indicating ST QTLs to be very specific to GB. Further, that 67.0% of the total 26 QTLs identified from the two sets of reciprocal introgression lines were also detected in the RILs that clearly brings out the background effect on ST QTL detection and its exploitation in ST breeding. Detection of ILs with varied levels of pyramiding of non allelic QTL effects for ST from Xiushui09 into favorable background i.e. IR2061 allowed us further improve the ST in rice.3. Identification of QTLs for cold tolerance at the seedling stage and heat tolerance at the anthesis using advanced backcross population in riceThe set of XS-ILs was used to identify QTLs associated with CT at the seedling stage and HT at the anthesis stage. As the results showed, 4 QTLs of survival rate of seedling in low temperature were mapped on chromosome 1, 7 and 11, respectively, which can explain 3.7%-8.7% of the phenotypic variance. As for HT, 8 QTL of spikelet fertility rate and 1000-seed weight were identified in normal condition and high temperature stress condition. These QTLs could be divided into three types based on their behaviors under different conditions: 6 QTLs can be identified under normal condition and explain 5.7%-45.6% of the phenotypic variance; 5 QTLs can be identified under high temperature stress and explain10.0%-12.3% of the phenotypic variance and the other 3 QTLs related to the difference between normal condition and high temperature stress can explain 5.0%-11.1% of the phenotypic variance. By compared with the results of CT and HT, one QTL related to both CT and HT was mapped on the near location on chromosome 7, which indicated partial genetic overlap between the two traits.4. QTL mapping for plant height under different conditions using advanced backcross introgression line populations in rice QTLs related to plant height were detected under the different conditions using the set of XS-ILs.The results showed environmental factors have a significant effect on plant height, and the different genetic mechanisms of plant height exist under different abiotic stresses in rice. 15 QTLs were mapped on all chromosomes of rice except chromosome 2, accounting for 3.8% -21.4% phenotypic variances. In Hainan, compared with the normal condition, the plant heights of parents are lower under drought stress and the plant height have a positive correlation with yield in the population under drought stress. Under normal and drought stress condition, 10 QTLs of plant height were detected and among these QTLs of plant height, 4 QTLs (QPh1a,QPh4,QPh11 and QPh12) were only identified under drought stress, indicating the presence of different underlying mechanisms. In Hangzhou, compared with the normal condition, the plant height of japonica parent are higher under heat stress, however it is lower for the plant height of indica parent and the plant height have a negative correlation with spikelet fertility rate in the population under heat stress. Under normal and heat stress condition, 11 QTLs of plant height were detected and some QTLs of plant height only expressed in one certain condition, which explained the reason of the difference of plant height variation between parents under heat stress. For all QTLs, only 2 QTLs (QPh3 and QPh12) could be detected under both drought stress and high temperature stress, suggesting that there are some genetic overlap between drought tolerance and high temperature tolerance although it is genetically independent for most loci.5. The detection of main-effect QTL and QTL by environment interaction of the traits related to yield using the two sets of reciprocal introgression lines and recombinant inbred linesThe genetic mechanism underlying 1000-seed weight (GW), spikelet number per panicle (SNP), fertility rate (SF), panicle number per plant (PN) and yield per plant (PY) was dissected using the two sets of reciprocal introgression lines and RIL under different conditions. The results showed, a total of 56 QTL were mapped and only 5 (8.9%) QTL were commonly detected in different populations under different conditions. As for the 56 QTLs related with yield traits, a concentrated distribution was observed and more than 80% loci were mapped on 13 certain chromosomal regions, which are useful for marker assisted selection and cloning the genes of yield. Meanwhile, we discuss the effect of expressions of related QTL under drought stress.
|
PDF Full Text Request