Mycotoxin Profile and Phylogeny of Pathogenic Alternaria Species Isolated from Symptomatic Tomato Plants in Lebanon

Abstract

The tomato is one of the most consumed agri-food products in Lebanon. Several fungal pathogens, including <i>Alternaria</i> species, can infect tomato plants during the whole growing cycle. <i>Alternaria</i> infections cause severe production and economic losses in field and during storage. In addition, <i>Alternaria</i> species represent a serious toxicological risk since they are able to produce a wide range of mycotoxins, associated with different toxic activities on human and animal health. Several <i>Alternaria</i> species were detected on tomatoes, among which the most important are <i>A. solani</i>, <i>A. alternata</i>, and <i>A. arborescens</i>. A set of 49 <i>Alternaria</i> strains isolated from leaves and stems of diseased tomato plants were characterised by using a polyphasic approach. All strains were included in the recently defined phylogenetic <i>Alternaria</i> section and grouped in three well-separated sub-clades, namely <i>A. alternata</i> (24 out of 49), <i>A. arborescens</i> (12 out of 49), and <i>A. mali</i> morpho-species (12 out of 49). One strain showed high genetic similarity with an <i>A.</i><i>limoniasperae</i> reference strain. Chemical analyses showed that most of the <i>Alternaria</i> strains, cultured on rice, were able to produce alternariol (AOH), alternariol methyl ether (AME), altenuene (ALT) and tenuazonic acid (TA), with values up to 5634, 16,006, 5156, and 4507 mg kg^-1, respectively. In addition, 66% of the strains were able to co-produce simultaneously the four mycotoxins investigated. The pathogenicity test carried out on 10 <i>Alternaria</i> strains, representative of phylogenetic sub-clades, revealed that they were all pathogenic on tomato fruits. No significant difference among strains was observed, although <i>A. alternata</i> and <i>A. arborescens</i> strains were slightly more aggressive than <i>A. mali</i> morpho-species strains. This paper reports new insights on mycotoxin profiles, genetic variability, and pathogenicity of <i>Alternaria</i> species on tomatoes.