Soil fumigation with ammonium bicarbonate or metam sodium under high temperature alleviates continuous cropping-induced Fusarium wilt in watermelon

The induction of Fusarium wilt by continuous cropping has become a severe problem for watermelon cultivation around the world. Here, the feasibility and underlying mechanism of soil fumigation with ammonium bicarbonate (AB) or metam sodium (MS) under high temperature (HT) were investigated for the control of Fusarium wilt during watermelon growth on continuously cropped soils. Both AB + HT and MS + HT decreased the density of Fusarium oxysporum f. sp. niveum (FON) in soil, improved the soil properties (i.e. increased the pH, reduced salinity, improved soil nutrients, balanced soil micro-ecology, and increased soil enzyme activities), and consequently decreased the Fusarium wilt incidence and improved the watermelon fruit quality. In vitro, MS treatment stopped the growth of FON on medium, while AB mixed with lime (but not AB) alone inhibited FON growth. AB or MS fumigated soils under HT also decreased Fusarium wilt incidence of watermelon seedlings after artificial FON infection. Consequently, AB + HT and MS + HT can control continuous cropping-induced Fusarium wilt by both inhibiting FON growth and improving the soil environment.