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Stemphylium lycopersici isolates virulence depends on the synthesis of phytotoxic metabolites, which is modified by the environment.

Pedro Balatti: Centro de Investigaciones de Fitopatologia (CIDEFI)

<div><em>Stemphylium lycopersici </em>is one of the causative agents of Tomato grey leaf spot. We found that the genome of <em>S. lycopersici </em>CIDEFI-216 contains several putative secondary metabolite (SM) gene clusters, which have been associated to different biological roles. We hypothesized that isolates of <em>S. lycopersici</em> that differ in their virulence and ability to sporulate synthesize a different array of SMs. Three isolates of the fungus that differ in virulence and sporulation capacity were grown on V8 and PDA plates at 25°C for 14 days. SMs were obtained from lyophilized cultures through sonication and ultrafiltration. Spectroscopic UV–Vis absorption spectra and fluorescence–excitation-emission matrices as well as phytotoxicity of the fungal extracts were evaluated. The absorbance spectrum showed that all the extracts had a 450-nm peak and that isolate CIDEFI-216 grown on V8 medium contained the most complete array of peaks, metabolites. Fluorescence intensity and emission was a function of the fungal isolate and the culture medium. Extracts from CIDEFI-216 presented the highest fluorescence emission spectra, and all of them provoked lesions on tomato leaflets (p<0.05), which were greater provided the fungus was grown in V8 medium. Here we demonstrate that SMs are key variable factors in the necrotrophic ability of <em>S. lycopersici</em> isolates, which can be drastically modified by the environment where the fungus grows.</div>