Studies On The Inheritance Of Powdery Mildew Resistance In Netted Muskmelon (Cucumis Melon L. Var. Reticulates Naud.)

Netted muskmelon (Cucumis melo L. var. reticulates Naud.) is a variety of melon species. It is well planted in China, Japan, Spain, Italy, America, Russia and Iran. China has been the first melon production country all over the world, both in area and yield. Nowadays, powdery mildew is one of the most important diseases in melon cultivation, and many researchers focus on this problem.In the present experiment, high powdery mildew resistant and susceptive lines and their offsprings were used to study the inheritance of resistant to powdery mildew in netted muskmelon, and the dynamic changes of some enzymes activities related to powdery mildew and MDA content were assayed as well before and after inoculation. On the aspect of molecular markers of powdery mildew resistance, we also did some preliminary studies. The main results were summarized as follows:1. By identifying the powdery mildew pathogen by investigate the symptom of xenogenetic disease in the field, microscope detection and back inoculation experiment, we found the powdery mildew in netted muskmelon was infected by Sphaerotheca fuliginea. Identified results both under field and greenhouse conditions with resistant (P₁) and susceptive (P₂) parents and their F₁, F₂, BC_1P1, BC_1P2 showed that the F₁ and BC_1P1 were resistant to powdery mildew, as the resistant parent did, the susceptive parent showed the symptom of powdery mildew, and population of F₂ and BC_1P2 were separated in resistant to powdery mildew. Statistical data showed that the practical ratio of resistant individuals to susceptive individuals in F₂ and BC_1P2 were fitted to 3:1 and 1:1, respectively. These results indicated that the resistance to powdery mildew was mainly controlled by one dominant gene. On the other hand, identified whit 25 cross combinations obtained from the complete diallel cross of 2 resistant and 3 susceptive parents showed that the hybrids were resistant or susceptive to powdery mildew depended on their parents, i.e., the hybrid will resistant to powdery mildew when one of its parent was resistant one, if the hybrid was obtained form two susceptive parents, it would show susceptive to powdery mildew. However, we found that the plants that ought to be resistant to powdery mildew in theoretically, were still showed slightly powdery mildew. This phenomenon indicated that except the main dominant gene, some modified genes existed which controlled the resistance of powdery mildew.2. Muskmelon leaves of resistant (P₁) and susceptive (P₂) parents and their F₁ were sampled 0 h (before inoculation), 2 h, 6 h, 24 h, 48 h, 96 h and 120 h after inoculation to assay the activities of superoxide dismutase (SOD), guaiacol peroxidase (G-POD), ascorbate peroxidase (APX), catalase (CAT), polyphenol oxidase (PPO), and MDA content. The result showed that there was a close relationship between powdery mildew resistance and the activities of SOD, G-POD, APX, PPO, CAT and MDA content. The activities of these enzymes showed up trend, and were higher than that of the CK (none inoculation). The enzymes activities of resistant parent were higher than that of the susceptive parent. In contrast, the MDA content of resistant parent was lower than that of susceptive parent. However, the dynamic changes of these enzyme activities were not the same pattern. The activities of APX, G-POD, CAT and MDA content in the three muskmelon leaves were increased steadily after inoculation, except the CAT activity of F₁ at 2 hours after inoculation. The SOD and PPO activities came though the changes of increase, and then decrease, and increase again, but the changes of trend were varied among the three netted muskmelon lines.3. We used RAPD technique and the method of bulked segregation analysis (BSA) to study the F₂ population constructed by the progeny of P₁ and P₂. Individual plant of the F₂ population was classified as resistant or susceptible group. According to the results of identification, we chose the most resistant individuals and the most susceptible individuals to construct two pairs of different gene pools to screen the RAPD marker linked to the resistant gene in the muskmelon. We found 6 primers with some different fragments among 48 primers used in the experiment, and one RAPD molecular marker was identified, which inked to powdery mildew resistant gene. And the primer RAPD-S60 could amplify the fragment, which is related to the resistance of powdery mildew.