Potato late blight epidemics and population structure of Phytophthora infestans

Potato late blight is caused by the fungus <em>Phytophthora infestans</em> . To study the relative importance of oospores in the epidemiology, and to estimate the relative impact of various infection sources, late blight epidemics in Southern Flevoland (The Netherlands) were studied using epidemiological and DNA fingerprint analyses. Infested refuse piles were the most important infection source for late blight epidemics in 1994 and 1995. Infected seed tubers were of minor importance.The results suggest that oospores play a role in the development of late blight in commercial potato crops, although the importance is less pronounced than refuse piles. Infested organic potato crops were important mid-season infection sources in 1994, but not in 1995 and 1996 due to unfavourable weather. In allotment gardens, oospores appeared to be the major inoculum for disease on potatoes and tomatoes in 1995 and 1996. Influx of inoculum from the commercial potato fields was evident in 1994, a year with a major epidemic in the first half of the growing season.A long-term study of late blight epidemics in The Netherlands from 1950 through 1996 indicated that the disease level in the previous year and the number of days with precipitation during the growing season were the most important factors determining the current year's disease level. A multi-year pattern was observed. The results described in the thesis suggest that the disease pressure may increase in the future.Potato late blight is caused by the fungus <em>Phytophthora infestans</em> . To study the relative importance of oospores in the epidemiology, and to estimate the relative impact of various infection sources, late blight epidemics in Southern Flevoland (The Netherlands) were studied using epidemiological and DNA fingerprint analyses. Infested refuse piles were the most important infection source for late blight epidemics in 1994 and 1995. Infected seed tubers were of minor importance.The results suggest that oospores play a role in the development of late blight in commercial potato crops, although the importance is less pronounced than refuse piles. Infested organic potato crops were important mid-season infection sources in 1994, but not in 1995 and 1996 due to unfavourable weather. In allotment gardens, oospores appeared to be the major inoculum for disease on potatoes and tomatoes in 1995 and 1996. Influx of inoculum from the commercial potato fields was evident in 1994, a year with a major epidemic in the first half of the growing season.A long-term study of late blight epidemics in The Netherlands from 1950 through 1996 indicated that the disease level in the previous year and the number of days with precipitation during the growing season were the most important factors determining the current year's disease level. A multi-year pattern was observed. The results described in the thesis suggest that the disease pressure may increase in the future.