Trichoderma harzianum T-E5 significantly affects cucumber root exudates and fungal community in the cucumber rhizosphere

• The root exudates inhibited the conidia germination of FOC by application of BIO.
• Phenolic compounds in root exudates were identified and quantified by HPLC.
• The population of FOC markedly reduced in cucumber rhizosphere by inoculation of T-E5.
• Significant differences in fungal community were found among treatments.
• Modified root exudates and fungal community accounted for disease incidence decrease.

The Fusarium wilt in cucumbers, caused by the pathogenic fungus Fusarium oxysporum f. sp. cucumerinum, is a serious and destructive disease worldwide. An effort was made to explore the role of Trichoderma harzianum T-E5 in reducing the incidence of Fusarium wilt. Three treatments (Control, T1, and T2) were established in the greenhouse experiment. The effects of T-E5 on the composition of root exudates and fungal community in the cucumber rhizosphere were measured. Compared with the control, the application of a bio-organic fertilizer (BIO) enriched with T-E5 was found to decrease the incidence of Fusarium wilt notably and promote the growth of cucumber plants. Based on real-time PCR, the population of F. oxysporum in the control without T-E5 increased from 103 to 104 ITS copies g−1 soil, whereas the population decreased from 103 to 102 ITS copies g−1 soil in the T1 and T2 treatment groups when T-E5 was included. Significant difference in fungal community was also found among the treatment groups. HPLC analysis showed that the detected levels of phenolic compounds in control were significantly higher than the levels in the samples subjected to T1 and T2 treatments. The root exudates from the control group significantly increased the numbers of germinating spores of the pathogen compared with those from the samples treated with T1 and T2. In conclusion, the modification of root exudates and the fungal community by the application of BIO might account for the effective suppression of Fusarium wilt disease in cucumbers.