POPULATION DYNAMICS OF METALAXYL SENSITIVE AND RESISTANT STRAINS OF PHYTOPHTHORA INFESTANS UNDER CONTROLLED ENVIRONMENT

develop resistance to the systemic fungicide metalaxyl within 2-3 years of its use in European countries (2). In India, a product of metalaxyl (Ridomil MZ 72 WP) was introduced commercially in 1988 and strains of P. infestans resistant to 5 ppm metalaxyl were encountered next year from a field sprayed with Ridomil MZ. Although, metalaxyl is sold as a mixture (metalaxyl + protectant fungicide), the information generated so far suggests that resistance to metalaxyl would develop even if fungicide(s) combinations are used continuously over a period of time (3, 9). Subtropical hills are the glaring example where level of metalaxyl resistance has gone up to 600 ppm (3). Population of fungicide resistant strains keeps changing over the years, but there is no precise information available as to how this population will behave if metalaxyl is used continuously over a period of time. The objective of the present investigation was to study the population dynamics of metalaxyl resistant (MR) and metalaxyl sensitive (MS) strains of P. infestans under controlled environment in presence and/or absence of metalaxyl.