Biological control of Fusarium oxysporum f. sp. cucumerinum causing cucumber wilt by Gliocladium virens and Trichoderma harzianum.

Antagonistic activities of 56 Gliocladium isolates and 9 Trichoderma isolates obtained from cucumber and strawberry fields, respectively, against Fusarium oxysporum f. sp. cucumerinum were tested in vitro. A Gliocladium GC27 isolate that inhibited mycelial growth of the pathogen remarkably by non-volatile antifungal antibiotics was identified as Gliocladium virens. Trichoderma harzianum T42 had the highest mycoparastic effect and low antibiosis to the pathogen. The antibiosis of G. virens GC27 to the pathogen was not affected by the type of nitrogen sources in the medium, but that of T. harzianum T42 with low antibiotic activity was increased by ammonium tartrate or NH4NO3. Addition of chitin, cell wall preparation of the pathogen, cellulose, and organic sources such as ground wheat bran, malt, rice straw and corn into synthetic medium had no effect on antibiotic activity of T. harzianum T42. Mycelial growth and conidial germination of the pathogen by G. virens GC27 were not affected by fungal cell wall components, whereas those were inhibited greatly by wheat bran or malt addition to the mineral medium. Addition of chitin or wheat bran into synthetic medium enhanced the mycoparastism of T. harzianum T42. The incorporation of G. virens GC27 or T. harzianum T42 cultured on wheat bran media into sterilized soil infested with the pathogen was much more effective in reducing the incidence of cucumber wilt caused by F. oxysporum f.sp. cucumerinum than the application of conidial suspension without organic food base was in pot experiments. The wheat bran culture of G. virens GC27 added with or without inorganic nutrients decreased the disease incidence by 54.2-59.1 % compared to that of control without antagonist. The application of wheat bran culture of T. harzianum T42 mixed with inorganic nutrients, also decreased the incidence of cucumber wilt by 52.3-59.7 %, whereas without inorganic nutrients mixture, disease incidence was reduced by only 18.2 %.