The QTL Mapping Of Cold Tolerance And Traits Related Yield At Seedling Stage For Shennong 265

Low temperature chilling damage mostly occured in Chinese high latitudes and some southern regions where spring cold was easy to occur.Rice was a cold sensitive crop.It was important to excavate cold-tolerant genes for improving cold-tolerant rice varieties.The super rice variety,SN 265,had many excellent characters such as high yield,good quality,tolerance to low temperature at seedling stage,etc.In order to excavate and utilize the excellent gene in this variety,and find stably expressed QTL of large contribution rate in different genetic backgrounds,It was used as the set crossed with two indica rice varieties Qishanzhan and IR30 to construct RILs populations(S1 and S2)as experimental materials.The study accomplished cold tolerance phenotype identification and evaluation at seedling stage,agronomic characters investigation,QTL mapping analysis of cold tolerance and yield related traits at seedling stage,and analysising the relationship between cold tolerance and yield related traits at seedling stage.The main results were as follows:(1)Cold tolerance phenotype of two RIL populations was identified at seedling stage.The population showed different degrees of resistance to low temperature after low temperature treatment at seedling stage.Cold tolerance of the population continuously distributed between grades 1-9.It indicated that there were different classes of cold tolerance materials in the population,which ensured the polymorphism of the target characters in the population.according to the mortality rate in S1 group,screened out 12 varieties of extreme cold tolerance at seedling stage,1 variety of cold sensitivity at seedling stage,their proportion was 10.2% and 0.8% respectively;screened out 10 varieties of extreme cold tolerance at seedling stage,7 variety of cold sensitivity at seedling stage,their proportion was 4.6% and 3.2% respectively in the S2 group.The statistical results showed cold resistant phenotype of two RIL populations was superaffinity separation state at the seedling stage,normal distribution trend for the cold tolerance,and abundant genetic variation of the two groups.(2)The ratio of dead seedlings was used an indicator of evaluation to inspect cold tolerance at the seedling stage under low-temperature treatment.Using genetic linkage map of two sets of populations and complete interval mapping method,the study identified 4 main effect quantitative trait loci(QTL)for cold tolerance at seedling stage and the additive effect were contributed by SN265.There were two QTLs on Chromosome 5 and Chromosome 6,qCTS-5.1and qCTS-6,detected in S1 population with contribution rate 47.59% and 22.47%,respectively.And LOD value was 6.54 and 4.88,respectively.In S2 population,two QTLs for cold tolerance(qCTS-5.2 and qCTS-7)were detected on chromosome 5 and Chromosome 7,explaining 22.62% and 38.48% of phenotypic variances,respectively.The LOD value is 10.00 and 9.81,respectively.Two sites qCTS-5.1 and qCTS-5.2 coincided with on chromosome 5 detected in S1 and S2 populations,respectively,the result suggested that it can express steadily under different genetic backgrounds.(3)For S1 and S2 groups,investigating plant height,panicle length,thousand kerner weight,etc,the results showed that the frequency trend of all traits were a pacific distribution with wide and rich genetic variation of controling yield traits,and most individual mutation rate was higher than the average,.Among the two populations,27 QTLs related to agronomic traits were detected.In the S1 population,the study detected 4 main genes which were qPH-1,qSSR-6,qSNP-1.1 and qPL-4.1 controlling plant height,grain number and ear length respectively.And in S2 population,it detected 3 main genes which were qPH-6,qTGW-3,qSNP-1.2 controlling plant height,thousand kerner weight and panicle grain number respectively(genetic contribution rate?15%).The marker interval of qSNP-1.1 in the S1 population was the same as that detected qSNP-1.2 in S2 population.So them were the same QTL.(4)Analyzing the correlation between seedling death rate at seedling stage and agronomic characters for two populations,the results showed that there was a significant negative correlation between seedling death rate and seed setting rate in both populations.There was a significant negative correlation between seedling death rate and thousand kerner weight.The results showed that there was no contradiction between cold tolerance and yield,which laid a theoretical foundation for breeding new lines with good yield and strong cold tolerance in molecular breeding.