Variation In Aggressiveness Components In The Hemileia Vastatrix Population In Brazil

The Pucciniomycete fungus Hemileia vastatrix causes leaf rust on coffee trees. The pathogen is responsible for considerable yield losses in susceptible coffee cultivars if appropriate management strategies are not implemented. Rapid spread and epidemics of rust fungi are usually associated with the emergence of new races of the pathogen that overcome resistance or with the emergence of more aggressive populations of the pathogen. In Brazil, coffee production is dominated by susceptible cultivars of Coffea arabica and Coffea canephora. We assessed aggressiveness in 46 populations of H.vastatrix from Minas Gerais and Espirito Santo, two of the most important coffee-producing states in Brazil. We observed a significant difference in the incubation period between the populations from Minas Gerais and Espirito Santo when 183 single-pustule isolates were inoculated onto Catuai Vermelho IAC 44, a susceptible C.arabica cultivar. Variation in aggressiveness components was observed between and within localities. Isolates with longer incubation periods also tended to have longer latent periods, although there was only a low correlation between these two aggressiveness components (r(2)=0.34, P=2.2x10(-16)). Low-sporulating isolates also had significantly longer incubation and latent periods. The H.vastatrix population from Minas Gerais and Espirito Santo is structured by the formation of groups of individuals with differential level of aggressiveness. Our results indicate that the variation in aggressiveness of the Brazilian H.vastatrix population may be associated with the geographic coffee-producing areas.