Construction Of A Genetic Linkage Map Of Rootstock-used Pumpkin And QTL Mapping For Chilling Tolerance

Chilling stress and salinity stress are two restraining factors for winter-spring protected cucumber(Cucumis sativus L.)cultivation.Grafting would increase the tolerance to chilling and salinity stresses and choosing the appropriate rootstocks would be the key to successful graft.Pumpkins(Cucurbita sp.)are annual herb trailing plants of Cucurbitaceae,Cucurbita,and representing a large germplasm resource for important traits such as adaptability,storage longevity,and tolerance to abiotic stresses;therefore,pumpkin species that are highly tolerant to various stresses are usually selected as rootstocks for cucumber grafting.We evaluated the tolerance of 15 pumpkin cultivars to chilling,salinity,and combined stresses at the germination and seedling stages in the study.A genetic linkage map was constructed by SSR markers and F2 population and we detected QTLs related to chilling index.The main results are as follows:1.In the present study,15 varieties of pumpkin(Cucurbita sp.)were tested under chilling stress,NaCl stress and combined stresses treatments at germination and seedling stages.Morphological parameters of pumpkin plant were measured and data were analyzed using Unweighted Pair Group Method with Arithmetic Mean(UPGMA)cluster analysis,to screen out the specific germplasms with multiple resistance.The results showed that these 15 pumpkin germplasms could be divided into three types:resistant cultivar,moderate resistant cultivar and susceptive cultivar according to their tolerance to the chilling stress,NaCl stress and combined stresses.The combination stresses resistance analysis showed that cultivar 'Bao Er','Chang Zhentielong','Da Wei 10','Da Zuotaimu','Jia Hetaimu','Kun Lun','Gen Lishen','Lv Ba',`Qiang Lishi','Shen Zhan','Victory','Hei Zinangua'showed multiple tolerances.Those cultivars could be selected as the rootstock germplasm for winter-spring protected cucumber grafting cultivation.2.An F2 population with 166 individuals was derived from a cross between a chilling-stress-susceptible high-generation inbred line('5-5-6')and a chilling-stress-tolerant high-generation inbred line('8-3-7').1277 SSR markers were screened for polymorphisms between the parental lines '8-3-7' and '5-5-6' and a molecular linkage map was constructed with 95 SSR markers,resulting in 15 linkage groups(LGs)covering a total distance of 830.7 cM with an average interval of 8.74 cM.The length of each linkage group ranges from 106.2 cM(LG1)to 9.0 cM(LG15)and the number of markers ranges from 15(LG8)to 2(LG7?LG15).3.Three QTLs were detected for CI based on the genetic linkage map with 95 SSR markers in 166 F2 population,explaining 0.30%,1.22%and 20.88%of the phenotypic variation,on LG1,LG4 and LG 10,respectively.