Morphological and Molecular Characterization of Large-spored Alternaria Species Associated with Potato and Tomato Early Blight in Egypt

Abstract

Early blight incurs huge losses to solanaceous crops at both pre-and post-harvest stages by reducing yields up to 35–78%. Large-spored Alternaria spp. were isolated and characterized from the symptomatic tomato and potato plants. Morphological characterization revealed heterogeneity in the different traits of the isolates, which were subsequently confirmed by molecular characterization and two different Alternaria spp. viz. A. solani and A. linariae were characterized. A multi-locus phylogenetic analysis was conducted to infer the taxonomic position of the isolates within Alternaria spp. The five conserved genome regions used to infer phylogenetic lineage and evolutionary relationship were the internal transcribed spacer (ITS), the translation elongation factor (TEF), the glyceraldehyde-3-phosphate dehydrogenase (GADPH), the major allergen Alt a1 (Alt a1) and the RNA-polymerase 2 (RPB2) genes. All A. linariae isolates were closely related and formed a clade to A. linariae isolated from the United States. Similarly, A. solani isolates were closely related to each other and formed an independent clade indicating their unique nature. Koch’s postulates were fulfilled for all the isolates. Among six different tested fungicides, aveet (azoxystrobin 5% + mancozeb 70%) inhibited the mycelial growth the most and saver (cymoxanil 5% + chlorothalonil 37%) the least. All the isolates infected tomato and potato leaves with varying severity except A. linariae isolate Egy-T2 was non-pathogenic on potato leaves, while the rest of A. linariae isolates were more aggressive. Here, we demonstrated that early blight in Egypt is caused by two different species of fungal pathogens, A. linariae and A. solani, and reported isolation of A. linariae from Egypt.