Effects of combination of hymexazol and Bacillus megaterium on Fusarium wilt of continuous cropping melon (Cucumis sativus L.)

In order to alleviate the harm caused by Fusarium wilt to continuous cropping melon, the soil obstacle degree from melon continuous cropping area in Qing County of Hebei Province was analyzed. Moreover, the effects of the combination of hymexazol and Bacillus megaterium on the growth and the alleviation effect of melon wilt were studied through indoor pots and field trials, and the preliminary analysis of the soil microbial community composition was performed. The results showed that the root-shoot ratio and whole plant dry weights of pumpkin and melon seedlings cultivated in continuous cropping soil for 11 years were significantly lower than those for one year. In addition, the number of bacteria and actinomycetes were the lowest, but the number of fungi was the highest in the soil with continuous cropping melon for 11 years. Meanwhile, the relative abundance of Fusarium was the most obvious, showing a significant difference from that in the soil for one year, the relative abundance of Bacillus in one year soil was 2.65 times that of 11 years soil. There was no antagonism between hymexazol and B. megaterium b1. The EC₅₀ of hymexazol and B. megaterium b1 to F. oxysporum T2 were 10.82 mg/L and 2.02 ×10⁵ CFU/mL, respectively. When 11 years of continuous cropping soil was used to cultivate melon seedlings and treated with hymexazol and B. megaterium b1 strain with EC₅₀ concentration, the controlling effects on melon Fusarium wilt were 42.85% in the melon flowering period, which was better than the treatments of hymexazol, B. megaterium b1 strain and blank control. The root-shoot ratio and the whole plant dry weight of melon seedlings treated with combination were promoted and significantly different from the single treatments and the control. The results of field experiments showed that the control efficiency of B. megaterium , hymexazol and combined agent to melon wilt on continuous cropping soil were 16.62%, 100%, and 100%, respectively. The melon plant height of each treatment was 11.19%, 10.63%, and 16.03% higher than that of the control, respectively. The yield increase rates were 20.35%, 11.23%, and 26.15% respectively. The average root dry weight per plant was 40.63%, 34.69%, and 64.38% higher than the control with significant differences (P<0.05), respectively. The number of fungi decreased whereas the number of bacteria and actinomycetes increased. The relative abundance of Fusarium was 35.96%, 59.55%, and 71.91% lower than the control, respectively. The relative abundance of Bacillus increased by 47.25%, 3.52%, and 76.70% compared with the control, respectively. The results indicated that the combination of hymexazol and B. megaterium could promote the growth of melon and relieve melon wilt in continuous cropping soil, effectively improve the soil microbial community composition, and alleviate continuous cropping obstacles.