§ Mr. RedmondTo ask the Minister of Agriculture, Fisheries and Food what research has been carried out in his Department into phytophthora infestans and with what result.
§ Mr. MacleanResearch conducted post-war by the advisory services has demonstrated the relationship between potato blight, caused by the fungus phytophthora infestans, and the economics of yield, and has determined the effects of weather on the proliferation of the disease from primary sources of infection in or near crops. This 831W work has led to the formulation, in collaboration with the Meteorological Office, of weather-based schemes to forecast the initiation of epidemics and the need to begin protective programmes of fungicide sprays to control the disease.
The most recent research has been concerned with the control of potato blight with fungicides representing groups with different modes of action. Recently the main objective has been to monitor the distribution and incidence of strains of p. infestans resistant to the commonly used systemic fungicides and to evaluate the efficacy of proprietary products against natural epidemics in the field.
Since 1986, resistance to phenylamide fungicides has been widespread in England and Wales. In 1988 and 1989, about 80 per cent. of potato blight samples contained p. infestans resistant to phenylamides. Consequently, the phenylamide component of fungicides for the control of potato blight has become unreliable. There have been no observations of resistance developing to other fungicide groups. Research has led to recommendations for the use of fungicides which will control the disease in the presence of phenylamide-resistance.
The effect of the timing of fungicide sprays in relation to irrigation has also been investigated. Applications of the fungicide mancozeb one day before, one day after or five days after irrigation were equally effective in controlling potato blight.
A survey of British potato crops (1986 and 1987) has shown that strains of p. infestans capable of stimulating sexual reproduction have entered the country. The risks of consequent genetic evolution towards more virulent strains of the pathogen, towards the development of insensitivity of fungicides, and towards the ability of such strains to persist in soil as viable spores are being evaluated.
The Ministry of Agriculture, Fisheries and Food has also funded work, co-ordinated by the National Institute of Agricultural Botany, on the evaluation of new varieties of potatoes. This work includes an assessment of varietal resistance to p. infestans, the results of which are made available in the National Institute of Agricultural Botany farmer's leaflet "Recommended Varieties of Potatoes."