Plant Growth-Promoting Potential of Colletotrichum sp. Isolated from Ocimum basilicum L. Leaves: A Broad-Spectrum Evaluation.

The primary objective of this study was to assess the growth-promoting potential of Colletotrichum sp. as a broad-spectrum plant inoculant and to investigate its applicability beyond its natural host range. Out of ten endophytes isolated from Ocimum basilicum, only four were reported for IAA production and among them, Colletotrichum sp. was chosen for further investigation due to its higher IAA production. Highest production of IAA was observed by providing Czapek dox broth with dextrose as carbon source, ammonium sulphate as nitrogen source at pH 7 and 32 °C. The crude fungal extract from Colletotrichum sp. was tested for its impact on rice plants under different application methods (soil drenching, foliar spraying, and seed immersion). Seed immersion treatment showed a notable effect on the growth of rice seedlings in contrast to soil drenching and foliar spraying. Plant growth assay with fungal elicitor treatment of plantlets produced by shoot culture, supplementing with 0.04 mL of culture filtrate per 30 mL media has significant impact on induction of rooting and overall biomass in Ocimum tenuiflorum as compared to untreated control plants. High-resolution liquid chromatography mass spectrometry (HR-LCMS) analysis of the fungal extract revealed the production of 3-indoleacetic acid and related intermediates.