Alternaria species associated with early blight epidemics on tomato and other Solanaceae crops in northwestern Algeria

Early blight is a common disease of Solanaceae crops worldwide. The occurrence of Alternaria spp. was studied during three epidemics on tomato in northwestern Algeria. Alternaria was detected in more than 80 % of the diseased plant samples and accounted for more than 50 % of the total fungal isolates recovered from these samples. Morphological and molecular investigations revealed that small-spored isolates producing beaked conidia, i.e. belonging to the section alternaria, were prominent in most of the surveyed locations representing more than 80 % of the total Alternaria isolates in three locations (Mascara, Ain Témouchent and Sidi Belabbèsse). Based on their sporulation patterns they were recognized as A. alternata and A. tenuissima. Small-spored isolates producing conidia without beak and assigned to A. consortialis were also found at a low frequency (< 1 %). Large-spored isolates producing conidia ended by typical long beaks and identified as A. linariae (syn. A. tomatophila), A. solani and A. grandis were also recovered from all the sampled areas and represented 33.8 %, 6.3 % and 1.3 % of the total Alternaria isolates, respectively. Pathogenicity tests on tomato with a selection of 85 strains representative of the isolates collection revealed that all the tested isolates were able to produce extending lesions on inoculated leaves albeit with variable intensity. Large-spored species included the most aggressive isolates. Small-spored Alternaria, although less aggressive than large-spored Alternaria, had the ability to provoke brown necrotic spots and circumstantially developed synergistic interactions in mixed infections with moderately aggressive isolates of A. linariae

A flavoprotein supports cell wall properties in the necrotrophic fungus Alternaria brassicicola

Background Flavin-dependent monooxygenases are involved in key biological processes as they catalyze a wide variety of chemo-, regio- and enantioselective oxygenation reactions. Flavoprotein monooxygenases are frequently encountered in micro-organisms, most of which require further functional and biocatalytic assessment. Here we investigated the function of the AbMak1 gene, which encodes a group A flavin monooxygenase in the plant pathogenic fungus Alternaria brassicicola, by generating a deficient mutant and examining its phenotype. Results Functional analysis indicates that the AbMak1 protein is involved in cell wall biogenesis and influences the melanization process. We documented a significant decrease in melanin content in the Δabmak1 strain compared to the wild-type and complemented strains. We investigated the cell wall morphology and physical properties in the wild-type and transformants using electron and atomic force microscopy. These approaches confirmed the aberrant morphology of the conidial wall structure in the Δabmak1 strain which had an impact on hydrophilic adhesion and conidial surface stiffness. However, there was no significant impairment in growth, conidia formation, pathogenicity or susceptibility to various environmental stresses in the Δabmak1 strain. Conclusion This study sheds new light on the function of a fungal flavin-dependent monooxygenase, which plays an important role in melanization