Identification of A. arborescens, A. grandis, and A. protenta as new members of the European Alternaria population on potato.

Alternaria species, primarily the small-spored Alternaria alternata and the large-spored Alternaria solani, are considered a serious threat to potato cultivation. To develop control strategies, it is important to gain insight into the Alternaria population. Based on the sequence analyses of the internal transcribed spacer region (ITS) and the glyceraldehyde-3-phosphate dehydrogenase gene, the small-spored and large-spored Alternaria isolates could be separated from each other. Sequence analyses of the calmodulin gene and the RNA polymerase second largest subunit showed that besides A. solani also A. grandis and A. protenta were present in the large-spored Alternaria population. Sequence analyses of the Alternaria major allergen gene Alt a 1 and the elongation factor-α revealed that both A. alternata and species belonging to the Alternaria arborescens species complex were present in the small-spored Alternaria population. Furthermore, according to the histone h3 sequence the members of the A. arborescens species complex could be subdivided into two groups. Concerning the fitness, it was concluded that the mycelium growth rate of the large-spored isolates was significantly lower compared to the growth rate of the small-spored isolates. In contrast, the spore-germinating capacity and early growth of the large-spored isolates was greater compared to those of the small-spored isolates. Within the groups of small-spored and large-spored isolates there were no significant differences in fitness between the species.