Alternaria from date palm. PHYLOGENY AND MYCOTOXIN PROFILES OF PATHOGENIC ALTERNARIA AND CURVULARIA SPECIES ISOLATED FROM DATE PALM, IN SOUTH TUNISIA

Date palm (Phoenix dactylifera L.), is widely cultivated across North Africa. In Tunisia, with about 300 thousand tons of fruits produced per year, date palm occupies a strategic place in the socio-economic stability of semiarid and arid regions. Several biotic and abiotic factors can compromise date palm cultivation. A wide range of fungal pathogens have been associated to date palm plants showing symptoms of leaf spots. However, Alternaria species are reported as the most frequent pathogens. Samples of symptomatic plant parts of the common Deglet Nour variety were randomly collected in six localities, in Tunisia. Among the fungal strains, we have selected 50 strains that, based on morphological features, were identified at genus level as Alternaria (45 strains) and Curvularia (5 strains). However, due to the high unreliability of identifying Alternaria and Curvularia strains at species level, only based on morphological features, wWe used phylogeny, analyses of mycotoxin profile and pathogenicity tests, as a polyphasic approach, to provide obtain the strainsa more accurate identification at species level. Sequencing of allergen-alt-1a, glyceraldeyde3-phosphate dehydrogenase (GPD) and calmodulin genes allowed us to group 35 strains, identified as A. arborescens, A. tenuissima and A. alternata species, in Alternaria Section, and 10 strains, identified as A. consortialis, in Ulocladioides Section. Based on combined Internal Transcribed Spacer, GPD and Elongation factor genomic regions sequencing analyses, all 5 Curvularia strains were identified as Curvularia spicifera. In addition, the pathogenicity of representative strains for each species was tested on date palm plantlets. All Alternaria and Curvularia species, tested on date palm plantlets, proved to be pathogenic, complying Koch’s postulates. Among the species, A. arborescens was the most pathogenic, while C. spicifera resulted to be the less aggressive. The capability to produce in vitro alternariol (AOH), alternariol monomethyl ether (AME), altenuene (ALT), tenuazonic acid (TA), tentoxin (TEN), and fumonisins was analyzed. All A. consortialis strains did not produced any mycotoxin, whereas more than 80 % of the strains included in Alternaria section produced very variable amounts of multiple mycotoxins such as AOH, AME, TEN and TA. In addition, 40 % of the Alternaria section strains produced also ALT. We tested also tThe production of fumonisins (FBs) was detected only by four out of the five , harmful mycotoxins related to esophageal cancer in humans and to many other animal diseases. Only, all Curvularia strains have shown the capability to produce fumonisinsanalyzed. This work reports a first comprehensive multidisciplinary study of mycotoxigenic Alternaria species and C. spicifera species associated to leaf spot disease on date palm, that includes both phytopathological and food safety issues.