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

Wassim Habib,Juan M Quiles,Giuseppe Meca,Antonia Susca,Elvis Gerges,Romy El Ghorayeb,Mario Masiello,Antonio F Logrieco,Antonio Moretti

doi:10.3390/toxins13080513

Abstract

The tomato is one of the most consumed agri-food products in Lebanon. Several fungal pathogens, including Alternaria species, can infect tomato plants during the whole growing cycle. Alternaria infections cause severe production and economic losses in field and during storage. In addition, Alternaria 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 Alternaria species were detected on tomatoes, among which the most important are A. solani, A. alternata, and A. arborescens. A set of 49 Alternaria 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 Alternaria section and grouped in three well-separated sub-clades, namely A. alternata (24 out of 49), A. arborescens (12 out of 49), and A. mali morpho-species (12 out of 49). One strain showed high genetic similarity with an A. limoniasperae reference strain. Chemical analyses showed that most of the Alternaria 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 Alternaria strains, representative of phylogenetic sub-clades, revealed that they were all pathogenic on tomato fruits. No significant difference among strains was observed, although A. alternata and A. arborescens strains were slightly more aggressive than A. mali morpho-species strains. This paper reports new insights on mycotoxin profiles, genetic variability, and pathogenicity of Alternaria species on tomatoes.

Highlights

The tomato is one of the most important agricultural crops produced and consumed in Lebanon
All genes were very informative for discriminating between Alternaria species, alt-a1 and calmodulin genes showed the highest degree of variability
Alternaria strains isolated from tomatoes, 17 Alternaria reference sequences and one strain of Stemphylium isolated from tomatoes (Altern1357) as the outgroup taxon (Figure 1)

Summary

Introduction

The tomato is one of the most important agricultural crops produced and consumed in Lebanon. Grown on about 3800 hectares, in open fields or in greenhouses, after potato the tomato is considered the second biggest agro-food crop in terms of production and consumption, with a volume of about 300,000 tons [1]. Almost all tomato production is consumed in Lebanon, and about 5000 tons per year are exported to the Arab gulf countries. Alternaria is a ubiquitous fungal genus that includes endophytic, saprophytic and pathogenic species commonly found in soil, air, food commodities, and on decaying plant tissues [5]. Alternaria species have been reported on important crops, including cereals, oil crops, ornamentals, vegetables and fruits [5,6]. Weakened or wounded tissues are more prone to being colonised by Alternaria species [7,8]

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