In order to study the inheritance of melon T115,founding the molecular markers linked to resistance genes and locating the resistance genes.Parental lines and(T115 SP Hongxincui) F₁,F₂,back cross populations BCr and BCs were scored for response to inoculation with[Pseudoperonospora cubensis (Berk.etCurt.) Rostov.].The simple sequence repeat(SSR) technique and bulk segregant analysis(BSA) were used to identify molecular markers linked to the resistance of melon downy mildew.A total 1 090 pairs SSR primers could detect the polymorphism between the resistant pool and susceptible pool which based on the ICuGI constructed genetic linkage map.The resistance to downy mildew in T115 was controlled by one single dominant gene. An unique 120 bp fragment was amplified with the primer DM0073.It was identified that was linked to resistance gene of T115 at a distance of 3.6 cM.The resistance gene was located to LG1.This SSR bands indicated that the marker could be useful for marker assisted selection in melon breeding for downy mildew resistance.

In order to study the inheritance of wild melon PI414723,founding the molecular markers linked to resistance genes and locating the resistance genes.The F₂,BCr and BCs populations were derived by crossing and back crossing with Cucumis melo ssp. melo lines PI414723 and kalakesai.Investigation and statistical analyses scored for response to inoculation with[Pseudoperonospora cubensis (Berk.etCurt.) Rostov.].Based on the genetic linkage map that was constructed by the ICuGI.SSR analysis,combined with bulked segregation analysis(BSA),was done on the DNA of F₂ using 1 090 pairs of SSR primers.The results indicated that the resistance to downy mildew in PI414723 was controlled by one single recessive gene. An unique 226 bp fragment was amplified with the primer DM0231.It was identified that was linked to resistance gene of PI414723 at a distance of 2.67 cM.The resistance gene was located to LG9.This SSR marker DM0231could be useful for marker assisted selection in melon breeding for downy mildew resistance.

In order to study the effects of different concentrations of cadmium stress on the growth and physiological characteristics of different thin-skinned melon varieties at seedling stage,hydroponic methods were conducted with based on previous experiments,and the thin-skinned melon varieties XTG(relatively high accumulation species)and IVF-28(relatively low accumulation species)were selected as trial cultivars. Four different CdCl₂ concentrations of 0,30,60,and 100 mg/L were set,the changes of shoot growth,root growth and physiological and biochemical indexes under different Cd stress concentrations were studied. The results showed that the plant height,stem thickness,total root length,root surface area,root volume,root tip number,and fractal dimension of XTG and IVF-28 all decreased as the concentration of Cd stress increased. And the decrease of XTG was lower than that of IVF-28. With the increase of Cd stress treatment concentration,the physiology of the two tested thin-skinned melon varieties also changed. The SOD,MDA and H₂O₂ contents increased with the increase of Cd stress treatment concentration,and the POD activity and GSH content reached the maximum under 60 mg/L CdCl₂ treatment,while CAT activity and PRO content reached the maximum when 30 mg/L CdCl₂ treatment,in which the physiological and biochemical indicators of XTG were higher than IVF-28. The results showed that X-T-G,a thin-skinned melon variety,had a lower decline in growth-related indicators than IVF-28 under Cd stress,and physiological indicators were higher than IVF-28,indicating that X-T-G had high tolerance to Cd stress than IVF-28.

To obtain the genes related to fruit maturation of melon, the genome-wide identification of four gene families, HB(Homeobox),RIN(Ripening inhibitor),ETR(Ethylene receptor) and CTR(Constitutive triple reaction) from melon, which were related to ethylene biosynthesis and signal transduction, were carried out in the study. A total of 17 members of CmHB family,21 members of CmRIN family,3 members of CmETR family and 20 members of CmCTRs family were retrieved from the melon genome, which were further verified by sequence alignment and motif analysis. Using transcriptional profiling analysis, the expressions of the four gene family members in wild type Cucumis melo L.cv Hetao and transgenic Cucumis melo L.cv Hetao with antisense CmACO1 gene (M9) were determined during growth period and at ripening stage of fruits. The results showed that 13 genes were differentially expressed between the two developmental stages of fruit in wild type melon, of which the expression amount of CmHB3 and CmHB11 in growth period was, respectively, 42 and 9 times that at ripening stage, but the expression level of CmHB4 at ripening stage was 27 times that in growth period, all reaching to a highly significant level. And 12 genes were also differentially expressed between two developmental stages of fruit in M9 transgenic line, among which the expression amount of CmHB3 and CmHB11 in growth period was, respectively, 6 and 3 times that at ripening stage, while the expression level of CmHB4 at ripening stage was 41 times that in growth period, all the differences being highly significant. During the growth of fruit, the expression levels of CmHB3 and CmHB11 had extremely significant difference, and the expression levels of CmRIN14 and CmRIN15 were significantly different between wild type and M9 fruits. At ripening stage of fruit, the difference in expression level of CmHB3 was highly significant and the differences in expression levels of CmRIN14 and CmRIN15 were significant between two types of melon fruits. In addition, the expression patterns of CmRIN14 and CmRIN15 between the two melon materials presented a opposite trend,indicating that their expression patterns were affected by the expression level of CmACO1.

Brassinosteriod is a necessary for plant to regulate the plant physical activities, and DWF1 is one of most critical enzymes involved in brassinosteriod biosynthesis. In order to study the function of DWF1 in melon fruit development, the gene CmDWF1 was cloned from melon for analyzing the nucleotide and amino acid sequences. RT-PCR method was used to analyze the gene expression characteristics. The results showed that the open read frame length of CmDWF1 was 1 701 bp, encoding 566 amino acids. The predicted protein molecular weight of CmDWF1 was 66.115 11 ku, the theoretical isoelectric point was 6.96, the instability index was 48.18 and the GRAVY was -0.402. Signal sequence was not found and the location coefficient in the cytoplasm was 9, which suggested that the protein was localized in cytoplasm. The secondary structure of CmDWF1 protein contained 37.81% of alpha helix, which was relatively high. The CmDWF1 protein contained a FAD-binding-4 domain, which suggested that the protein acted as a FAD oxidoreductase. Phylogenetic analysis showed that Cucumis melo had closer relationship with Cucumis sativus. Real-time fluorescent quantitative analysis indicated that CmDWF1 could express in roots, stems and leaves, but the highest expression level was in roots. And the expression level increased significantly in the 25 d fruit after pollination, but decreased in 35-45 d fruit. These results demonstrated that CmDWF1 might be associated with the biosynthesis of brassinosteriods and then regulated the growth and development of melon.