Effect of Difenoconazole on the Formation of Oospores by Phytophthora Infestans (mont) De Bary

Fungicide difenoconazole is applied for field treatment to protect potato and tomato against early blight, caused by the Alternaria fungi. It is practically important to estimate the impact of difenoconazole application against late blight pathogen Phytophthora infestans (Mont.) de Bary because of early and late blight often come together on potato. Effect of fungicide difenoconazole on the radial growth of colony of P. infestans and the formation of oospores in agar media and in detached leaves was investigated. There was no significant influence of difenoconazole on the radial growth of P. infestans colony, small inhibition occurred only at high concentration of fungicide (100 mg/l). Difenoconazole inhibited the oospore formation in the medium with positive dependence on concentrations of fungicide and temperature increasing. Tested in leaves difenoconazol inhibited the oosporogenesis with positive dependence on concentrations of fungicide also. The tiers of the plant were considered as source of oospores with different potential. In laboratory conditions (test on detached leaves) the higher production of oospores was detected in leaves from middle and low tiers rather than from top tiers.