Species diversity, novel interactions and absence of well-supported host-guided phylogenetic groupings of Neotropical Alternaria isolates causing foliar lesions in Solanaceae.

Abstract

To report the characterization of 120 Alternaria isolates inducing early blight-like foliar lesions in nine species of five Solanaceae genera collected across all macrogeographical Brazilian regions. Phylogenetic relationships were assessed via analyses of the Alternaria alternata allergenic protein-coding, glyceraldehyde-3-phosphate dehydrogenase and the calmodulin gene sequences. Most of the tomato isolates were placed into the Alternaria linariae cluster, whereas most of the potato isolates were grouped with Alternaria grandis. Novel host-pathogen interactions were also reported. Seventeen isolates were selected for morphometrical characterization, and a subsample of 13 isolates was employed in pathogenicity assays on tomato, potato, eggplant, scarlet eggplant, Capsicum annuum, Datura stramonium, Physalis angulata and Nicotiana tabacum. Eleven isolates were able to induce foliar lesions in tomatoes but none in C. annuum. Potato was susceptible to a subgroup of isolates but displayed a subset of isolate-specific interactions. Morphological traits were in overall agreement with molecular and host range data. Alternaria linariae and A. grandis were confirmed as the major causal agents of tomato and potato early blight, respectively. However other Alternaria species are also involved with early blight in solanaceous hosts in Brazil. The diversity and host-specific patterns of the Alternaria isolates from Solanaceae may have practical implications in establishing effective early blight genetic resistance and cultural management strategies especially for tomato and potato crops.