The relationship between Bakanae disease severity (Gibberella fujikuroi) and gibberellic acid produced by the fungus causal agent on Sepidroud cultivar rice

Bakanae disease and foot rot of rice Gibberella fujikuroi (Sawada) is one of the seed-borne diseases that its conspicuous symptoms are elongated, narrow and pale seedlings from contaminated seeds that is caused by gibberellin-producing isolates of pathogen. The aim of present investigation is determination of the disease severity index (DSI) of the fungus G. fujikuroi and its relationship with rate of gibberllic acid production by the fungus in the rice Sepidroud cultivar. The sampling of infected plants from rice fields, isolation and purification of fungus was done. All of isolates cultivated in a specific medium for production of gibberellic acid. Amount of the hormone produced by isolates of pathogen was determined by HPLC. The inoculation of plant stem was done by injection of conidial suspension of pathogen at the end of booting and the beginning of panicle exertion stages in the Sepidroud cultivar and disease severity was evaluated. According to the results of this study, significant correlation was not found between the disease severity of G. fujikuroi and the amount of production of gibberellic acid in pathogen on rice Sepidroud cultivar.