| The improvement of drought tolerance in rice is an arduous and long-term task.QTL mapping,fine mapping and gene cloning of drought-related traits,and the realization of molecular breeding for drought tolerance,is the hot research in recent years.QTL mapping in rice is mainly focused on root,such as root thickness,root length,root number and root distribution,as well as physiological characteristics,such as ABA, osmotic adjustment,RWC and so on,and positioned a large number of QTLs.However, further research using of these large population to carry out fine mapping,there exists great difficulty in real work.In this research,we constructed NILs and narrow down the interval to fine mapping in target interval in an RIL population of 520 lines from a cross between an indica paddy rice and upland japonica rice.Main results of the present are as following:1.Fine mapping was done to narrow down the interval by adding more SSR and Indel markers for the target interval of chromosome 2,chromosome 4,and chromosome 7.For the target interval RM561～RM341 on chromosome 2,we develop and synthesis 57 pairs, which 47 pairs have polymorphisms and 23 pairs were used to constructed the map.For the target interval RM273～RM255 on chromosome 4,we develop and synthesis 96 pairs, which 52 pairs have polymorphisms and 20 pairs were used to constructed the map.And For the target interval RM134～RM420 on chromosome 7,we develop and synthesis 26 pairs,which 22 pairs have polymorphisms and 9 pairs were used to constructed the map.2.In 2007,under the condition of drought stress,we survey the yield traits in the target interval of Chr2,Chr4 and Chr7.The NILs has higher yield and spikelet fertility than Zhenshan97B as the recurrent parent.In 2008,The ANOVA result showed significant difference between water treatments except PL in the target population of Chr2.Highly significant positive correlation between GY and BY,then PW,HI,GNP,PN,SN,SPD and SF under well-watered condition,while under drought stress condition,PW has highest positive correlation with GY,then GNP,HI,BY,SF,SN,SPD,PN and PL.Path analysis partitioned the correlation coefficients into direct and indirect effects.In well-watered condition,BY had the highest direct effect on GY,followed by HI,SN,PN,PW,SF, HGW,GNP,PL and SPD.While in drought stress condition,HI had the highest direct effect on GY,followed by BY,GNP,PW,SN,PN,HGW,PL,SPD and SF.The path coefficient was not consistent with correlation coefficient.3.Quantitative trait loci(QTL) mapping was carried out for grain yield,yield components and other drought-tolerant relative traits in the target interval of Chr2 in rice under normal water condition and drought stress in 2008.Based on composite interval mapping method at the threshold LOD≥2.0,under normal water condition,total 11 main-effect QTLs were detected for PL,PN,SF,HGW,IHD,HD,PH,TN,PND,SPD and CT. While under drought stress treatment,total 9 main-effect QTLs were detected for PN, LWP,HGW,IHD,HD,BCT,TN,SPD and CT.Different place and different repeats detected different QTLs,and in the hot interval RIO02052～RM02002,several QTLs were simultaneously or adjacently identified under two contrastive water conditions in different repeats,and find 5 putative genes in this hot points.4.In the target interval of Chr4,we detected 3 QTLs for PL,PN and SN.The QTL for PL was identified in different interval RM17308～RM17305 and RM17349～RM17190,and the contributions were 18.8%and 20.42%.The QTL for PN was identified in the interval RM1354～RM17308,and the contribution was 11.47%.The QTL for SN was identified in the interval RM17308～RM17305,and the contribution was 28.08%.5.In the target interval of Chr7,Combined with molecular markers and phenotypic traits,and based on composite interval mapping method at the threshold LOD≥2.0,we didn't detect any QTLs.
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