Alternaria diseases on potato and tomato.

Alternaria spp. cause different diseases in potato and tomato crops. Early blight caused by Alternaria solani and brown spot caused by Alternaria alternata are most common, but the disease complex is far more diverse. We first provide an overview of the Alternaria species infecting the two host plants to alleviate some of the confusion that arises from the taxonomic rearrangements in this fungal genus. Highlighting the diversity of Alternaria fungi on both solanaceous hosts, we review studies investigating the genetic diversity and genomes, before we present recent advances from studies elucidating host-pathogen interactions and fungicide resistances.

Taxonomy: Kingdom Fungi, Phylum Ascomycota, Class Dothideomycetes, Order Pleosporales, Family Pleosporaceae, Genus Alternaria.

Biology and host range: Alternaria spp. adopt diverse lifestyles. We specifically review Alternaria spp. that cause disease in the two solanaceous crops potato (Solanum tuberosum) and tomato (Solanum lycopersicum). They are necrotrophic pathogens with no known sexual stage, despite some signatures of recombination.

Disease symptoms: Symptoms of the early blight/brown spot disease complex include foliar lesions that first present as brown spots, depending on the species with characteristic concentric rings, which eventually lead to severe defoliation and considerable yield loss.

Control: Good field hygiene can keep the disease pressure low. Some potato and tomato cultivars show differences in susceptibility, but there are no fully resistant varieties known. Therefore, the main control mechanism is treatment with fungicides.