Growth promotion of cucumber by pure cultures of gibberellin-producing Phoma sp. GAH7

The beneficial effects of plant growth promoting fungi (PGPF) on plant growth and development are well documented. However, limited information is available on gibberellin (GA) production capacity of PGPF of endophytic origin. In current study, 11 fungal endophytes were isolated from cucumber roots and then screened on Waito-C rice, in order to identify plant growth promoting fungal strains. The fungal isolate GAH7 provided the maximum shoot length (11.3 cm) in comparison to control treatment (7.8 cm). In a separate experiment, bioassay of GAH7 significantly promoted growth attributes of cucumber. The GAH7 culture filtrate (CF) was found to contain physiologically active gibberellins in higher concentrations (GA₁, 0.81 ng/ml; GA₃, 4.34 ng/ml and GA₄, 9.31 ng/ml) in conjunction with physiologically inactive GA₉ (0.74 ng/ml), GA₁₅ (0.97 ng/ml), GA₁₉ (1.67 ng/ml) and GA₂₀ (0.46 ng/ml). Isolate GAH7 produced higher amounts of GA₃, GA₄, GA₉ and GA₁₉ than wild type Fusarium fujikuroi, which was used as control for GA production. Gibberellins were analyzed through gas chromatograph/mass spectrometer (GC/MS) with selected ion monitoring (SIM). The fungal isolate GAH7 was later identified as a new strain of Phoma on the basis of sequence homology (99%) and phylogenetic analysis of 18S rDNA sequence.