Distribution of large-spored Alternaria species associated with early blight of potato and tomato in Algeria

Potato and tomato are important crops in Algerian agriculture, and both are threatened by abiotic and biotic stresses, and early blight is a major disease affecting both crops. Surveys carried out from 2012 to 2015 in 12 major growing regions for these crops yielded a total of 247 Alternaria isolates having morphological and cultural characteristics of sections Alternaria and Porri. Since early blight symptoms and morphological characteristics of the isolates did not allow sharp distinction between the different large-spored species of Alternaria, the isolates in section Porri, often considered primary causes of the diseases, were selected for molecular characterization by diagnostic PCR using specific primers. This allowed species identification of 147 Alternaria isolates as A. solani, A. protenta, A. grandis or A. linariae. These species were present on potato and tomato crops at varying frequencies, depending on the hosts and on bioclimatic locations. Pathogenicity tests for the four species, on detached leaflets and whole seedlings, showed that all were pathogenic to potato and tomato, with varying virulence. These results suggest that parasitic specialization of these Alternaria species on solanaceous plants should be reconsidered.