Increased aggressiveness of Alternaria macrospora, a causal agent of leaf blight in cotton monoculture

Abstract

The monoculture of cotton now practised in Israel results in annual outbreaks of leaf blight epidemics. Pathogenic isolates of the casual agent, Alternaria macrospora, were field collected for six years, and inoculated onto cotton plants under controlled environmental conditions. Aggressiveness (virulence and fitness) of the pathogenic isolates increased over the years. The modified aggressiveness was manifested as follows: an increase in the number of lesions per leaf; an increase in the size of the lesions; a decrease in the time required for symptom expression; an increase in the viability of the pathogen spores after exposure to a normally lethal temperature; and a decrease in the wetting period required for symptom expression. Agricultural monoculture appears to have accelerated evolution in the aggressiveness of this plant leaf pathogen. -from Authors