Bacillus velezensis HZ33 Controls Potato Black Scurf and Improves the Potato Rhizosphere Microbiome and Potato Growth and Yield

Potato black scurf, caused by Rhizoctonia solani, is a widespread soil-borne disease in major potato-producing regions that reduces potato yield and tuber marketability. This study evaluated the field growth-promoting effects and disease-control efficacy of Bacillus velezensis HZ33 on the potato cultivars Xindaping and Longshu 7 and assessed its impact on rhizosphere microbial communities. Field trials showed that the application of HZ33 significantly enhanced potato growth and increased the chlorophyll content, yield, and commercial tuber rates. HZ33 also raised key soil nutrient levels. Its control efficacy against potato black scurf exceeded that of the chemical fungicide azoxystrobin. Application of HZ33 reduced the relative abundance of Rhizoctonia associated with black scurf and increased the relative abundance of beneficial fungi and bacteria. The microbial community structure correlated with both soil chemical properties and the disease index for potato black scurf. Overall, B. velezensis HZ33 appears to be a promising biocontrol agent for suppressing potato black scurf while improving potato yield.