Factors involved in the development of potato late blight disease (Phytophthora infestans)

Abstract

Late blight, caused by infection by the fungus Phytophthora infestans, is the most serious disease of potatoes and can completely destroy a crop. Blight is controlled by frequent applications of fungicides to the foliage, but there is increasing concern over the liberal use of agrochemicals. Loss of tuber yield depends on the amount of green foliage destroyed by the disease which, in turn, depends on the timing of the onset of blight and the rate of increase in blighted foliage. Modelling potato blight attempts to describe disease onset and progress using as input the many factors that affect blight.

Sexual reproduction of P. infestans, resulting in the formation of oospores, is probably important in the survival of the fungus in the field and in increasing the genotypic diversity of P. infestans. However, most of the build-up of disease results from the asexual reproductive cycle that consists of spore germination, infection of foliage, colonisation of foliage, sporulation, and spore dispersal and survival. The different stages in the asexual cycle of reproduction are affected by environmental factors that are largely determined by weather conditions and genotypic and physiological features of the pathogen (P. infestans)and the host. Most factors affecting blight interact with each other in complex ways, and their effects are difficult to quantify. Furthermore, many factors change continually and also vary horizontally and vertically within a crop, so the development of a realistic model for potato late blight is not easy.