Gibberellin production and plant growth promotion from pure cultures of Cladosporium sp. MH-6 isolated from cucumber (Cucumis sativus L.)

Gibberellin (GA) production by soil fungi has received little attention, although substantial work has been carried out on other aspects of plant growth promoting fungi (PGPF). In our studies we investigated GA production and growth-promoting capacity of a novel fungal strain isolated from the roots of soilgrown cucumber. Pure cultures of 19 endophytic fungi were tested for shoot length promotion of Waito-C rice to identify the GA production capacity of these fungal isolates. Isolate MH-6 significantly increased shoot length (12.9 cm) of Waito-C, in comparison to control treatments. Bioassay with culture filtrate (CF) of MH-6 also significantly promoted growth attributes of cucumber plants. Analysis of MH-6 CF showed the presence of physiologically active (GA1, 1.97 ng/mL; GA₃, 5.18 ng/mL; GA₄, 13.35 ng/mL and GA₇, 2.4 ng/mL) in conjunction with physiologically inactive (GA₉ [0.69 ng/mL], GA₁₂ [0.24 ng/mL], GA₁₅ [0.68 ng/mL, GA₁₉ [1.94 ng/mL and GA₂₀ [0.78 ng/mL]) gibberellins. The CF of MH-6 produced greater amounts of GA₃,GA₄,GA₇ and GA₁₉ than wild type Fusarium fujikuroi, a fungus known for high production of GA. The fungal isolate MH-6 was identified as a new strain of Cladosporium sp. on the basis of sequence homology (99%) and phylogenetic analysis of 18S rDNA sequence.