Comparative fitness of Alternaria species causing leaf blotch and fruit spot of apple in Australia

The reason for the high prevalence of the Alternaria arborescens species group compared to other species groups associated with leaf blotch of apple in Australia is not well understood. In order to determine if A. arborescens has a biological fitness advantage over the other species groups, this study compared the mycelial growth rate, fecundity and competitive spore production attributes of three isolates of each of four Alternaria species groups and examined the relationship between saprophytic and pathogenic fitness traits. Overall, this study revealed that the fitness attributes of the Alternaria isolates are significantly different among and within each of the species groups and suggests a strong relationship exists between high aggressive isolates and fast mycelial growth rate. A possible trade-off between fecundity and mycelial growth rate and contribution of mycelial growth rate in host invasion processes and factors that contribute to prevalence of the Alternaria species groups associated with leaf blotch and fruit spot of apple in Australia are discussed.