Intercropping with aerobic rice suppressed Fusarium wilt in watermelon

Watermelon is susceptible to Fusarium wilt in successively mono-cropped soil. Pot experiments were carried out to investigate the effect of intercropping with aerobic rice on Fusarium wilt in watermelon. The tested soil was classified as a loam soil, previously planted with watermelon and collected from Hexian county, Anhui province, China. The results obtained are listed as follows: (1) 66.7% of watermelon plants were infected with wilt disease and 44.4% died on 40 days after transplanting in mono-cropped soil, but plants were much less susceptible to infection when intercropped with rice; (2) the density of Fusarium oxysporum f. sp. niveum decreased by 91% in soil from the intercropped watermelon rhizosphere when compared with that from the mono-crop 40 days after transplanting; (3) densities of bacteria and actinomycetes increased, but fungal density decreased in rhizosphere soil from the intercrops in comparison with the mono-crop control; (4) compared to the control, the germinated Fusarium spores were decreased by 41.0% in the treatment with addition of 1.5 ml rice root exudates. Adding 20 ml of root exudates decreased Fusarium spore production by 76.4%; and (5) the activities of defense enzymes in the leaves and roots of watermelons in the intercropped system were significantly lower than those in the mono-cropped system. It is suggested that intercropping with aerobic rice alleviated Fusarium wilt in watermelon, by restraining the spore production of Fusarium and by changing the microbial communities in rhizosphere soil through the production of rice root exudates.