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

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 EC₅₀ 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 EC₅₀ 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.