Identification of Alternaria spp. associated with tomato early blight in Iran and investigating some of their virulence factors

Tomato is one of the major crops grown in Iran, which is attacked by a large number of pathogens. Early blight is among the most important and harmful diseases of this plant caused by Alternaria spp. This study was conducted to identify Alternaria species causing early blight disease and to evaluate different virulence factors of this fungal pathogen. The samples were collected in Khorassan-Razavi province in Iran from tomato plants showing characteristic symptoms of the disease. Morphological identification of the isolates was done on PCA medium and under controlled conditions. Six Alternaria species, including A. alternata, A. tenuissima, A. arborescens, A. mimicula, A. interrupta and A. infectoria were identified. The ITS1 and ITS4 primers were used for molecular identification of the isolates via sequence analysis. The highest frequency was observed for A. alternata and the least frequent was A. infectoria. All isolates obtained in this study were pathogenic on tomato cultivar Peto Early Ch. The results showed significant differences in pathogenicity of the isolates on tomato plants. A. alternata and A. tenuissima had the highest and A. mimicula and A. infectoria had the lowest level of pathogenicity. In the qualitative analysis of cell wall degrading enzymes (CWDEs), all tested isolates were able to produce pectinase, cellulase, amylase, protease and lipase, but production of pectinase and cellulase had direct correlation with pathogenicity of the isolates.