Diversity between different Gibberella fujikuroi isolates on their gibberellin hormone production and disease severity in rice plant

Bakanae disease of rice is one of the most important rice diseases all over the worlds. Elongation is one of the conspicuous symptoms of Bakanae disease that is caused by gibberellins-producing isolates of the pathogen. The present investigation was done to reconsider the species of Bakanae, the ratio of pathogen’s species, virulence, gibberellin production and the relationship between virulence and the rate of gibberellin production in 23 isolates by gathering 50 samples of infected plants from rice fields. In order to identify the disease severity, inoculation of the plant stem was done by injection of spore suspension at the seedling stage in the Gohar variety. Results led us to identify two species of pathogen Fusarium fujikuroi and Fusarium verticillioides, and each one of them had a population of 88.4 and 11.6%, respectively. Results of the pathogenicity test showed that inoculation of the seedling causes infection in all the plant. Furthermore, the disease severity caused by the tested isolates were different in all the host plants. Results from tests of gibberellin determination using spectrophotometry and HPLC methods revealed that all the isolates were able to produce the hormone but the amount of it differed among isolates. No significant correlation was observed between the amount of gibberellin and percentage of stem elongation (disease severity). Perhaps, it may be due to early effects of virulence ability of the pathogen in comparison with late effects of gibberellin in the host plant. This leads to a lack of relationship between gibberellin levels and the disease severity of the pathogen.