Study of the Development of Acquired Resistance to Fungicides in Pyricularia oryzae the Causal Organism of Rice Blast in Relation to Environmental Factors

Abstract

Rice is one of the main cereal crops. In Egypt rice is considered an important source of national income.

In Egypt, rice blast disease was recorded in most governorates to cause great losses. Recently one of the main problems restricting chemical control of plant disease is that pathogens could acquire resistance to many recommended fungicides. The present investigation aimed to estimate the development of acquired resistance in the natural population of Pyricularia oryzae to different fungicides to different isolates in relation to acquired resistance level and studying the possible change in the morphological and physiological characteristics of resistant isolates aiming to develop a prediction model and place strategy to control disease.

The resistance level in a natural population of P. oryzae to recommended fungicides was established in mycelium as well as in the spores. The different isolates differed markedly in their reaction to different concentration of the tested fungicides.

Successive subcultivation of sensitive isolates of P. oryzae (Gemiza931) on banana medium agar amended with sublethal dose of each of the yotal fungicides for 6 items resulted in gradually increasing in the resistance.

Successive subcultivation of a resistant isolate of P. oryzae (Kellin932) on banana medium agar free of any fungicide resulted in gradually loosing of the resistance.

Studying the effect of irradiation with UV rays on the development of the fungicidal resistance indicated that irradiation with UV ray was more induceable to resistant mutants to Beam and Fuji-one but not to Hinosan.