Distribution of Alternaria species on blighted potato and tomato leaves in Russia

Alternaria species are the causal agents of potato and tomato early blight disease. Three species-specific PCR primer sets were designed for Alternaria alternata sensu lato, Alternaria solani and Alternaria infectoria identification. The specificity of primers was confirmed by the absence of amplified products after PCR with DNA of Alternaria spp., other potato and tomato pathogenic fungal species and plant DNA. Constructed primers were applied for the survey of early blight agents on affected potato and tomato leaves collected in different regions of Russia. All three Alternaria pathogens were present in blighted leaves alone or in complex (A. alternata + A. solani, A. infectoria + A. alternata and A. solani + A. infectoria). Alternaria alternata (sensu lato) was the most abundant species. It was detected in 50% of tested potato leaves and 41% of tested tomato leaves (alone or in complex). Alternaria solani was found in 30 and 35% leaves, respectively. Alternaria infectoria occurred in potato and tomato samples occurred at a somewhat lower frequency (13 and 8%, respectively). Using the specific primers, it was possible to exclude the Alternaria disease in some leaves with symptoms similar to early blight.