Root Exudates From Different Cucumber Disease-resistant Cultivars And Its Effects On The Pathogen Of Cucumber Fusarium Wilt

Cucumber Fusarium wilt is an important soil-born disease limiting vegetable production worldwide. Root exudates may play an important role affecting acitivity of its causual agent, Fusarium oxysporum f.sp. cucumerinum (Foc), in soil. For better understanding the occurrence of the disease, the author analysed the exudates from both resistant and susceptible cucumber cultivars and its relationship with the occurrence of the disease.A fast and accurate method was established to detect Foc in the soil The detection limit was 2ng/g, And it was spiecies-specific, other species of Fusarium in the soil could not interfere the detection of Foc.Root exudates were collected from susceptible cultivar Jinyan 4 and and resistant cultivar Zhongnong 10, respectively. Effects of cucumber root exudates on the population of Foc in rhizoshpere were determined with real-time PCR. Results showed that the population dynamics of Foc in rhizosphere of resistant and susceptible was totally different from each other. At the fourteenth day after cucumber planting, the populations of Foc in resistant and susceptible cucumber rhizosphere were at their lowest and highest levels, with LgQ reaching 2.76±0.40 and 4.60±0.40,respectively. It was 14 days delayed that Foc population in resistant cucumber rhizosphere began to increase in comparison with the case in susceptible cultivar. Tests of the effects of root exudates on the survival of Foc in natural soil showed that root exudates from resistant cultivar shortened the survival period of Foc, while that from susceptible cultivar could prolong the survival period of Foc when compared with each other. In order to understand the phenomenom, the impacts of the methanolic extract (ME) and aqueous extract (AE) of extract of cucumber root exudates on the growth of Foc were studied. The results showed that the methanolic extract (ME) of resistant cultivar Zhongnong 10 could inhibit the growth of pathogen and ME of susceptible cultivar Jinyan 4 could stimulate it. Difference between ME of both cultivars was analyzed and identified using LC-MS/MS. Compound 7,8-Benzoflavone(7,8-BF) was detected only in root exudates from the resistant cultivar Zhongnong 10, with amount 0.02μg per plant in cucumber root exudates at seedling stage.Further research on the fungi-inhibitive activity of the compound against Foc showed that both growth and spores germination of the fungus were significantly inhibited at concentration 50μg/ml. The growth of radicals and the formation of lateral roots of resistant and susceptible cultivars were suppressed at the concentration of 100μg/ml of 7,8-BF. And Zhongnong 10 was more tolerant than Jinyan 4. Seeds treatment with 7,8-BF reduced significantly the disease index (DI) of both resistant and susceptible cultivars. The DI of the susceptible cultivar was reduced at 50μg/ml from 71.7 to 30.8. This research demonstrated that 7,8-BF from root exudate played an important part in occurrence of cucumber Fusarium wilt disease. However, more researches are needed to be sure that the compound exists extensively in resistant cucumber cultivars and is of effect on the disease in field. Research on this topic is of significance in understanding the occurrence and therefore managment of the disease.