Relationships between climatic conditions and potato late blight epidemic in egypt during winter seasons 1999–2001

Late blight is a disease of potatoes caused by Phytophthora infestans (Montagne) de Bary, the fungus can destroy virtually 100% of the above-ground parts of susceptible cultivars under favourable environmental conditions and in the absence of any control measures. Sever epidemics of late blight have emerged in both 1999/2000 and 2000/2001 growing seasons. An indicator variable for the occurrence of outbreak during the season based on the number of favourable days in terms of temperature and relative humidity during November to January was used to describe the disease status throughout the tested period. Weather conditions prevailing during potato-growing winter seasons were studied and compared in three potato-growing areas during 1998/1999 and in five growing areas during 2000/2001. Infection efficiency is a function of the environmental conditions and the potato cultivars. Mild and warm nights allow the disease to become established on first-early cultivars. This build-up of inoculums early in the year leads to a tendency for blight to appear in later-planted potato crops in the area sooner than it does in other regions. Wet warm winter seasons were identified as important factors influencing development of the recent late blight epidemics in Egypt. Most of the nights minimum temperature in November and December 1998/1999 were relatively cool in all of potato-growing areas, so, the disease had not built up the inoculums which are needed to start epidemic. While in November and December at 1999/2000 and 2000/2001 growing seasons at Badrashin, Kom Hamada, and Salhia which had relatively warm nights and the rainfall fairly early in November and December 2000/2001 and this occurred again on following days. So, the disease had built up the inoculums for starting epidemic. However, Bosaily and Kafr El- Zayat had cool nights during both seasons.