Identification of the roselle root rot pathogen and its sensitivity to different fungicides

Root rot is the main disease affecting roselle plantings and production and can seriously affect the yield and quality of calyces. Thus, it is urgent to identify the pathogen causing roselle root rot and screen effective pesticides to control the disease. In the present study, morphological observation, pathogenicity assays and molecular biology methods were used to identify the pathogen causing roselle root rot in Nanning, Guangxi Province, and four biological and four chemical fungicides were evaluated for their effects on the mycelial growth rate of the pathogen. The results showed that the pathogen causing roselle root rot in Nanning, Guangxi, was Fusarium solani, marking the first report of this fungus causing root rot of roselle in China. The fungicidal activity screening revealed differences in the inhibitory effects of the eight fungicides on the colony growth of F. solani. For the biofungicides, Bacillus amyloliquefaciens exhibited the best fungistatic effect, with an IC50 of 1.10 mg/mL. When the mass concentration was 2.5 mg/mL, the mycelial growth of the pathogen was 100% inhibited, while Bacillus subtilis had the worst inhibitory effect, with an IC50 of 46.78 mg/mL. When its mass concentration was 80 mg/mL, mycelial growth was only inhibited by 74.67%. For the chemical fungicides, carbendazim and thiophanate-methyl presented the strongest effects on F. solani, with IC50 values of 0.0082 mg/mL and 0.0243 mg/mL, respectively. When the mass concentrations were 0.03 mg/mL and 0.075 mg/mL, mycelial growth was inhibited by 100%. These results provide a scientific basis for rationally selecting fungicides to control roselle root rot in field production.