COMPARATIVE AGGRESSIVENESS OF METALAXYL RESISTANT AND SENSITIVE ISOLATES OF PHYTOPHTHORA INFESTANS

Abstract

Data on comparative growth rate, zoosporangial germination and aggressiveness of metalaxyl resistant (MR) and metalaxyl sensitive (MS) isolates of P. infestans collected from different parts of the country revealed that MR isolates excelled MS isolates in all respects. The MR isolates showed higher growth rate than the MS isolates on rye agar media. Zoosporangia of MR isolates were more efficient in germination as compared to those of MS isolates. Further, zoosporangia from MR isolates having 100, 50, 25 and 10 ppm tolerance exhibited 87%, 72.8%, 64.1% and 56.6% germination, respectively as compared to 43.3% germination for MS isolate. MR isolates also showed more aggressiveness and competitiveness when compared with MS isolates using composite fitness index (CFI). 100 ppm tolerant isolate showed highest aggressiveness (CFI-72429) followed by 50 ppm (CFI-71459) and 25 ppm (CFI-49339) isolates.