Mining Genes With Cold Tolerance Of Elite Germplasm In Cucumber

Cucumber is an important thermophilic vegetable crop and widely cultivated in north of China.But,chilling damage is still an key factor of restricting its yield increase in production in winter and early spring.therefore,selecting chilling tolerance materials,finding genes with cold tolerance and breeding new varities with cold resistance are important problems in cucumber.In this study,the tolerance to low temperature at seeding stage of elite germplasm resources were identified and evaluated in order to screening different germplasm resources with high cold tolerance;According to reported informations on cold tolance,genes related with cold tolerance in cucumber were selected and analyzed in germplasm resources with different level of cold tolerance;RIL population with 2 parents with large difference in cold tolerance were whole genome resequenced and high density genetic linkage map were constructed,QTLs associated with cold tolerance at shoot stage were identified and analyzed.Above results will provide an insight to further mining genes with cold tolerance of elite germplasm resource in cucumber.The main research results are as follows:1? Twenty-one germplasm which have good traits such as high resistance to disease were selected based on previous identification results of agronomic traits and resistance to natural low temperature in field firstly.The identification of cold tolerance at seedling stage were performed using the method of 6 ? constant low temperature stress and comprehensive evaluation were analyzed using the method of membership function.The tolerance to low temperature of 21 materials were divided into five levels including high resistance(HR),resistance(R),middle resistance(MR),low resistance(LR)and sensitive(S).The high resistance germplasm is from Liaoning province of China and its chilling injury index and recovery index were 17.0% and 72.7% respectively.2? We selected Based on reported informations on genes related with cold tolerance mainly in Arabidopsis thaliana and cucmber.Twelve genes with cold tolerance in cucumber were selected preliminarily and analyzed in 2 germplasm with great diferance of cold tolerance,then 5 genes with obvious different expression were determined further,which were analyzed finally in 5 germplasm with different level of cold tolerance.It resulted that the expression of Csa4M642460 and Csa1M423150 exibited relatively high in germplasm with cold tolerance and relatively low in germplasm with cold sensitive,especially at later stage during low temperature stress.These genes might be associated with the molecular mechanism of cold resistance at the stage of seedling in cucumber.3? Using whole genome sequencing technique,we detected 302710 polymorphism SNP markers and finally obtained 1495 Bin markers for linkage analysis.A genetic map containing 7 linkage groups were constructed,which covered genome length 855.563 c M,the average genetic distance was 0.6 c M between markers and there were 146~292 markers in different linkage groups,the length was 91.267~143.201 c M.4? Eight QTLs associated with cold tolerance at shoot stage were detected futher.Among them,4 QTLs with the index of relative germination rate located at chromosome 4 and 6 and their phenotypic contribution rate were 22.65%,13.91%,6.09%,5.63% respectively,2 QTLs with the index of relative radicle length located at chromosome 4 and 7 and their phenotypic contribution rate were 12.73% and 9.60%,other 2 QTLs associated with the index of relative fresh weight were also found at chromosome 4 and 7.Among them,there are a overlap on chromosome 4 between relative germination rate and relative radicle length,a overlap on chromosome 7 between relative radicle length and relative fresh weight.