Mapping Quantitative Traits Loci For The Heat Tolerance In Cucumber

Cucumber (Cucumis sativus L) is an important vegetable crop. Both in open field and in protection field it suffered from heat injury, which severely influenced the crop production. Thermoduric varieties or hybrids of cucumber is one of the most effective approach to avoid the heat injury. However, the effect of thermoduric breeding depends on the discovery of genetic mechanism and molecular mechanism. Molecular marker technology will be contributed to exploreing the useful information in efforts to develop resistant germplasm efficiently through locating the QTL relevant to heat tolerance. This study used F₂ population derived from 631-1(heat tolerance)×602(heat sensitive) to construct molecular marker linkage map and identify heat tolerance. Heat tolerance of the parents and F₂ population were identifyed. In addition, a molecular marker linkage map was constructed with SSR and RAPD marker, and QTL ananlysis was performed with composite interval mapping(CIM). The main results were as followed:In this study, the factors which affected on the SSR-PCR reaction in cucumber were studied including the concentration of dNTP, primer, Mg²⁺, DNA template, Taq DNA polymerase. The optimal reaction system was determined,that was as followed: the 20μl reaction system contained dNTP 200μmol/L,Primer 0.4μmol/L,Mg²⁺ 2.5mmol/L,Taq DNA polymerase 0.5U,DNA template 60ng and 1×PCRbuffer.F2 population which included 281 individual derived from 631-1(heat tolerance)×602(heat sensitive), and the heat tolerance was identifyed and analyed. Verification of normal distribution of identifyng effects were carried out, and the absolute values of skew degree and peak degree were smaller than 1. Results indicated that the frequence distribution of electric conductivity percentage in the F2 population were a normal distribution and the effect met the requirement to perform the mapping of QTLs.86 pairs of SSR primers and 132 RAPD primers were screened on the parent and the DNA mixing pool of the progeny. Results showed that 4 pairs of SSR primers and 7 RAPD primers were related with heat tolerance of cucumber. A molecular marker linkage group was constructed using Mapmaker/EXP version 3.0b, and four markers (N14,N12,N11 and N4) located to the same linkage group. By the software of Windows QTL Cartographer V2.0 and the method of composite interval mapping, three QTLs were detected for heat tolerance of cucumber. The distance between QTL loci and marker were 10.0cM,12.9 cM and 16.0 cM, respectively. They can explain genetic variability 6.18%,10.36% and 10.56% .