7,8-benzoflavone in root exudates of cucumber and its effect on Fusarium wilt occurrence.
The impacts of the methanolic extract (ME) and aqueous extract (AE) of cucumber root exudates on the growth of Fusarium oxysporum f. sp. cucumerinum (Foc), the pathogen of cucumber wilt disease, were studied. The results showed that ME of resistant cultivar Zhongnong 10 inhibited the growth of pathogen and ME of susceptible cultivar Jinyan 4 stimulated. Difference between ME of both cultivars was analyzed and identified by 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 of 0.02 µg per plant in cucumber root exudate at seedling stage. Further research on the fungi-inhibitive activity of the compound against Foc showed that both hyphal growth and spores germination of the fungus were significantly inhibited at a concentration of 50 µg/mL. The formation of lateral roots of resistant and susceptible cultivars were suppressed at the concentration of 100 µg/mL of 7,8-BF. Zhongnong 10 was higher tolerant than Jinyan 4. Seed 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 from 71.7 to 30.8 with 50 µg/mL of 7,8-BF.