Abstract:Fusarium wilt disease, caused by formae speciales of the fungus Fusarium oxysporum f. sp. niveum (FON) is a serious problem for the watermelon production around the world. Among the managements for controlling Fusarium wilt disease, pre-planted fumigation of soil is one of the most effective and stable means for the disease inhibition. In this study, the possibility of applying the fumigation agent, dazomet, to watermelon planting field with a novel bio-organic fertilizer (BOF) was investigated as a strategy for controlling Fusarium wilt of watermelon and improving the bio-chemical properties of a continuously cropping soil. Three treatments including control (CK), dazomet fumigation plus organic fertilizer (OF) and dazomet fumigation plus the bio-organic fertilizer (BOF) were set in the field experiment. Compared with CK, BOF and OF treatments significantly reduced Fusarium wilt disease incidence by 65.8% and 54.1%, respectively. BOF treatment increased watermelon yield, sugar content and sugar/acid by 33.4%, 15.9% and 13.4%, respectively. Soil fumigation with dazomet for 20 days significantly decreased the numbers of soil microbial organisms compared with pre-fumigation and non-fumigated control (CK). Through the estimation by realtime PCR method, the copy number of FON was decreased by 3 log units, the activities of urease, invertase, fluorescein diacetate esterase were significantly reduced by dazomet fumigation. Principal analysis of the Biolog AWCD showed that fumigation altered the microbial community. The Shannon diversity index and evenness index were significantly reduced when compared with CK. The amendment of organic fertilizer or the bio-organic fertilizer after dazomet fumigation restored the numberof microbial organism, the activity of soil enzymes and microbial functional diversity, and both the recovery speed and strength of soil microbial population and enzyme activities were maximal, the FON population and FON/fungi ratio were least, Shannon index was highest under BOF treatment during the whole growing season. These results suggest dazomet fumigation could significantly reduce the number of FON and could recover soil microbial flora faster and enhance enzyme activities if combined with bio-organic fertilizer. Thus, it could prevent watermelon plants from being re-infected by FON, reduce Fusarium wilt disease incidence significantly, and increase effectively the yield and quality of watermelon.