Competition Between Metalaxyl-Resistant and -Sensitive Strains ofPseudoperonospora cubensison Cucumber Plants

Publisher Website
Google Scholar
Abstract
The infectivity of 2 pairs of metalaxyl-resistant and -sensitive strains of P. cubensis was compared in the absence of metalaxyl selection pressure by single strain inoculations, passing mixed (1:1, 1:6 and 1:20 resistant:sensitive in initial sporangial suspension inoculum) strains through 2 inoculation cycles on intact cucumber cotyledons in growth chambers and exposing cucumbers growing in plastic houses to both strains (at a ratio of 1:1 or 1:4). With single strain inoculation, strains were equally infective to cucumbers. In mixed strain inoculations in growth chambers, after 1 sporulation cycle (2 successive inoculations) the original 1:1, 1:6 and 1:20 ratio of resistant:sensitive components changed essentially to 1:0. In mixed strain inoculations in plastic houses, the original 1:1 and 1:4 ratio (resistant:sensitive) changed essentially to 1:0 after 12-17 and 23 days, respectively. With the technique used to monitor strain frequency, the 2 metalaxyl-resistant strains of the fungus compete favorably with the 2 metalaxyl-sensitive strains in the absence of the fungicide.