Identification And QTL Mapping Of Drought-resistance Traits Of Cultivar Rice(O.sativa L.)Introgression Lines

In this study,a few pure lines(D123,D29,D121,etc)derived from continuous backcross between donor parent Haogelao,a landrace upland rice from Yunnan China,and recurrent parent Shennong 265,a Super Rice cultivar from Liaoning China,were used to identify their agronomic and physiological response to drought stress.Shennong265,Haogelao,IRAT109(drought-tolerance cultivar)and 297-28(drought susceptible pure line)were used as CKs.Mapping population was constructed by one more backcross between strong drought-resistance introgression line D123 and Shenong265.The drought related traits of the population were evaluated at seedling and maturity stages.QTL mapping of important drought-related traits were conducted using SSR markers.The major results are as follows:1.All introgression lines out-yielded Shennong265 with partly significant difference under well-watered conditions.Under water stress conditions,most introgression lines performed significantly better than Shennong265 in anti-leaf senescence level,grain yield,maximum root length and thick root number/total root number.In particular,the grain yield of D29 far exceeded its recurrent parent and was in accordance with IRAT109.The root length of D29 was significantly longer than all other genotypes tested,including IRAT109 and Haogelao.From the results,we can conclude that it is feasible to improve drought tolerance of paddy rice through backcross breeding strategy to achieve the goal of breeding new varieties combining drought tolerance and high yield potential.2.In diurnal variation analysis,the water potential of all genotypes at every time point were close to each other under well-watered condition and higher than their corresponding values under water stress condition with a maximum difference at 14:00-15:00.D123 was the same water potential type to upland rice cultivar Haogelao and IRAT109 as it displayed almost the same water potential performance to Haogelao and IRAT109 and no significant difference was observed at 14:00-15:00 comparing well-watered and water stress conditions.Although water potential of D121 were relatively low under both well-watered and water stress conditions,the water potential under severe drought condition was almost equal to that under well-watered condition.The water potential of D29 dropped significantly by drought stress at 14:00-15:00,but its water potential ranked the first in all genotypes under both well-watered and water stress conditions,indicating an outstanding physiological drought resistance characteristics.But different mechanisms of drought resistance might underlie in the two introgression lines.3.Diurnal variation of photosynthetic rate demonstrated that diurnal variation curve of well-watered condition was changed by drought stress and the photosynthetic rate peaks disappeared.Under 2012 rainfed environments,introgression lines D123 and D121 showed significantly higher photosynthetic rate than Shennong 265.The photosynthetic rate of D123 was almost equal to IRAT109 and Haogelao which were superior to other genotypes.Under 2013 rianfed environment,the photosynthetic rate of all introgression lines except D78 were significantly higher than Shennong 265.The results suggested improved photosynthetic rate conferred to ILs and more excellent performance was stimulated under severe drought stress conditions.4.The correlation analysis showed that extreme positive significant correlations or significant positive correlations existed between grain yield and biomass,setting percentage,thousand grain weight,photosynthetic rate;biomass and water potential,photosynthetic rate;water potential and photosynthetic rate,stomatal conductance,thick root diameter;photosynthetic rate and the thickest root diameter.But these correlations were insignificant under well-watered condition.No significant correlation was observed in basic seedlings,tiller number,filling tiller number and grain yield.On one hand,grain yield was affected by biomass at earlier stage.On the other hand,the grain yield of introgression lines was determined by drought-resistance related traits at later stage.Furthermore,the accumulation of biomass was positively related with water metabolism and photosynthesis processes and finally affected grain yield.Plant water potential in vivo affected photosynthesis directly and then exerted influence on grain yield indirectly.Thicker roots means stronger ability to absorb water from deep soil and transport water under drought stress to shoot to maintain vigorous water metabolism and high photosynthetic efficiency,which is one of the most important root characteristics of drought resistance genotypes.5.Population A and B(178 and 314 lines respectively)were constructed by screening about 7000 lines derived from backcross between D123 and Shennong265.49 and 58 lines performed steadily were identified from population A and B,respectively.15 lines with good comprehensive characters on plant height,yield,lodging resistance and anti-leaf senescence level were selected,providing good genetic materials for further drought tolerance research and breeding.Different sensibility response levels underlay in traits by identification drought resistance of population A and B.The sensitivity rank were setting percentage>height from ground to tassel tip>height from ground to leaf tip>tiller number>panicle length.Visual scoring of anti-leaf senescence level was a reliable method to evaluate drought tolerance by multiple years' trials.6.Four major QTLs were mapped under water stress conditions.Five QTLs controlling panicle length,delayed heading date and anti-leaf senescence level enriched between RM270 and RM3455 on chromosome 12.qan-lsl-4 on chromosome four located between RM255 and RM1153,which derived from Haogelao's fragment RM255-RM2799,indicating a recombinant occurred by backcross between D123 and Shennong265.qsp-11 controlling setting percentage located between RM1761 and RM21 on chromosome 11,which also derived from Haogelao.But no recombinant happened.More backcross should be conducted to recombine the fragment in the future.Fragment RM3455-RM2529 derived from Haogelao located on chromosome 12 enriched qan-lsl-12-2 and qpl-12-1,which could explain the phenotypic variation 94.63%and 15.36%,respectively.Main attention will be paid to these fragments in future research.The backcross between D123 and Shennong265 narrowed drought tolerance fragments,which laid a reinforced foundation for fine mapping and even drought resistant gene cloning.