Comprehensive analysis of Fusarium spp. associated with red stele root rot of strawberry (Fragaria ananassa) in northern Zhejiang, China

• This study identified the pathogen of strawberry red–stele root rot through morphology and molecular method. • Conducted research on the biological characteristics of pathogen. • Studied the indoor toxicity determination of four types of biocides against pathogen. • Field efficacy experiments were conducted on the four types of biocides mentioned above. In recent years, strawberry red–stele root rot has caused significant economic losses for growers in northern Zhejiang, China. Isolates were identified using morphological traits and molecular biological analysis,Koch’s postulates was established by re-isolation of strains from the inoculated roots. Biological characteristics were determined, and fungicide sensitivity was assessed in vitro with the mycelial–growth‐rate assay. Two species— Fusarium oxysporum and F. solani —were confirmed as the main pathogens causing strawberry red–stele root rot. For both fungi, optimal mycelial growth occurred at 25 °C under a 12-h light/12-h dark photoperiod; the optimal pH values were 7.0 for F. oxysporum and 6.0 for F. solani . Optimal conidial production for F. oxysporum was observed at 25 °C, pH 7.0, and 24 h light, whereas F. solani sporulated best at 30 °C under a 12 h light/12 h dark cycle. In vitro , 300 million spores/g Trichoderma harzianum and 0.3 % matrine emulsifiable concentrate (EC) strongly inhibited pathogens, the EC 50 values of 300 million spores/g Trichoderma harzianum for F. oxysporum and F. solani are 6.42 ± 1.40 mg L −1 and 8.58 ± 2.39 mg L −1 , respectively, while the EC 50 values of 0.3 % matrine for F. oxysporum and F. solani are 2.50 ± 1.31 mg L −1 and 0.73 ± 0.21 mg L −1 , respectively.Field efficacy tests showed that 300 million spores/g Trichoderma harzianum and 0.3 % matrine EC provided the best control effect, both reducing disease incidence to 35.00 %, lowering the disease index to 27.67 and 26.33, and achieving a controlled efficacy of 63.59 and 65.36 %, These findings clarify the etiology of strawberry red–stele root rot in northern Zhejiang and offer practical guidance for its diagnosis and control.