Phytopathogenic Fungi Pestalotiopsis Sensu Lato and Analysis of Their Secondary Metabolites

Abstract

The importance of Pestalotiopsis and Neopestalotiopsis species as pathogens of economically important plants is steadily increasing, while knowledge of their phytotoxic metabolites remains limited. Eighteen new strains of pestalotioid fungi were isolated from various plant samples that showed visible symptoms of disease. These strains were evaluated morphologically, and phylogenetic analyses of the ITS (internal transcribed spacer) and tub2 (beta-tubulin) gene regions were performed for genotyping. The isolated strains from Castanea sativa wood and nut were assigned to the species Neopestalotiopsis clavispora (six strain) and P. chamaeropis (one strain); four strains of Neopestalotiopsis, and one strain of Pestalotiopsis were not identified at the species level. Five strains isolated from coniferous trees, such as cypress and fir, were assigned to the species P. monochaeta, P. verruculosa, P. hollandica, and N. chrysea. A strain isolated from the Vaccinium uliginosum L. shoot was diagnosed as N. megabetaspora. The pathogenicity of strains was confirmed in vitro on coniferous shoots, Granny Smith apples, and leaves of C. sativa. The most pronounced phytopathogenic properties were demonstrated by strains isolated from C. sativa and a blueberry shoot compared to strains from coniferous trees. The dihydropyrans pestalotin and 7-hydroxypestalotin were identified in these strains, except for P. chamaeropis. The strains, isolated from cypress and fir, mainly produced a range of other metabolites. The extracts of the strains exerted a phytotoxic effect on lettuce root growth, suggesting that the metabolites may be involved in the virulence of the phytopathogenic fungi Pestalotiopsis s.l. Using the extract of Pes21 N. megabetaspora—the most active producer of pestalotins—we demonstrated that the necrosis area on the leaves of V. uliginosum L. and Rubus idaeus L. increased consistently with increasing metabolite concentrations. Purified pestalotin and 7-hydroxypestalotin inhibited lettuce root growth at a concentration of 500 μg/mL and stimulated it at a concentration of 100 μg/mL. This work provides important insights into the regulatory role of metabolites in fungus–plant interactions and serves as a basis for developing new strategies for the maintenance of plant resources.