Aiming at the problems of plant growth inhibition, frequent Fusarium wilt and microbial community imbalance caused by continuous cropping obstacle of watermelon, the effects of Helianthus tuberosus straw biochar on growth promotion, disease inhibition and microbiological mechanism were explored.

Two kinds of H. tuberosus straw biochar were used as test materials, and four treatments were set up, including 1% (w/w) biochar-continuous cropping soil mixed treatment (denoted as J04 and J13, respectively), carbendazim control (Y) and blank control (CK). The effects of biochar on the growth of watermelon seedlings and the occurrence of Fusarium wilt were investigated by pot experiment. The effects of H. tuberosus straw biochar on soil bacterial community structure and diversity were analyzed by Miseq high-throughput sequencing technology.

Compared with CK, the two biochar treatments significantly promoted the accumulation of watermelon seedling biomass and reduced the Fusarium wilt disease index. At 35 d after transplanting, compared with CK, the whole plant dry weight of J04 and J13 treatments significantly increased by 10.8% and 27.6%, the incidence significantly decreased by 28.8% and 48.5%, and the disease index significantly decreased by 21.1 and 30.8. The incidence of carbendazim treatment (Y) was significantly lower than that of CK by 59.1%, the disease index was significantly decreased by 38.1, and the dry weight of the whole plant was significantly increased by 4.3% (P＜0.05). Compared with CK, the α diversity of soil bacterial community in J04 and J13 treatments decreased significantly, and the Shannon index and Invsimpson index were significantly lower than CK. H. tuberosus biochar treatment significantly changed the soil bacterial community structure (R² =0.690, P=0.009). At the phylum level, J13 treatment significantly increased the relative abundance of Actinobacteriota and Firmicutes, and inhibited Acidobacteriota and Myxococcota. At the genus level, J13 treatment significantly enriched potential beneficial bacteria such as Gemmatimonas and Devosia. The FAPROTAX function prediction further indicated that J13 treatment significantly increased the abundance of microbial groups related to functions such as chemical heterotrophy and urea decomposition, which may promote the rhizosphere nutrient cycle.

The addition of H. tuberosus straw biochar (J13) can effectively alleviate the continuous cropping obstacle of watermelon, and its growth-promoting and disease-inhibiting effects are closely related to the improvement of rhizosphere bacterial community structure and the enrichment of potential beneficial bacteria with specific functions.