EFFECT OF ABIOTIC FACTORS ON SURVIVAL OF Phytophthora infestans AND MANAGEMENT OF LATE BLIGHT OF POTATO THROUGH CHEMICALS

In vitro and in vivo trials were conducted to check the effect of temperature, photoperiod and soil temperature and also the efficacy of systemic and contact fungicides for controlling the late blight of potato, Phytophthora infestan. The maximum growth of zoospore germtube of all the P. infestans isolates was achieved at temperature 24°C with 16h of photoperiod and minimum at temperature 30°C. The rest of temperature viz., 18, 21, 27°C were not suitable in enhancing germtube length. Maximum recovery of pathogen from the potato field in the presence of soil, naturally infected with P. infestans was recorded at temperature ranges of 15-30°C. Radial growth of P. infestans was greatest at 25°C. Soil temperatures that were recorded during certain times of the years in potato field were found to be inhibitory to sporulation and growth of the pathogen. Wet foliage was best in inducing the disease with artificial spray of the spores of pathogen @ 105 spores/ml. Systemic fungicide Ridomil @0.25% was found to be superior compared to Dithane M-45 (@ 0.25%) . The percent late blight incidence in potato crop sprayed with dithane M-45 ranged between 0- 6.2%, while with ridomil, sprayed potato crop showed almost complete control of the disease and its incidence ranged between 0-1.8%.