In vitro antifungal effect of phenylboronic and boric acid on Alternaria alternata

The ascomycete fungus Alternaria alternata causes early blight, one of economically the most important tomato diseases. Due to frequent use of fungicides, A. alternata has developed resistance with negative economic and environmental consequences. Research of new ways to control fungal pathogens has turned its eye to environmentally friendly chemicals with low toxicity such as boronic acids. The aim of our study was therefore to test the antifungal effects of phenylboronic and boric acid in vitro on A. alternata. We isolated the pathogen from a symptomatic tomato plant and determined the minimum inhibitory concentration of phenylboronic and boric acid on A. alternata mycelial growth using the poisoned food technique. The antifungal effect was tested on a wide range of phenylboronic and boric acid concentrations (from 0.04 % to 0.3 %) applied separately to agar with mycelial disc of the pathogen. After five days of incubation, phenylboronic acid at low concentration (0.05 %) completely inhibited mycelial growth. Boric acid, in turn, did not significantly slow down mycelial growth but did reduce sporulation and confirmed its fungistatic effect. Our findings point to the potential use of phenylboronic acid to control phytopathogenic fungi. This is, to our knowledge, the first report on its antifungal effect on an agriculturally important pathogen in vitro. Moreover, since A. alternata is also a human pathogen, these results may have clinical ramifications.Askomicetna gljiva Alternaria alternata uzročnik je koncentrične pjegavosti, jedne od ekonomski najvažnijih bolesti rajčice. Zbog česte primjene fungicida, ta je gljiva razvila otpornost na agrokemikalije koje se koriste u njezinu suzbijanju, s negativnim ekonomskim i ekološkim posljedicama. Novi načini suzbijanja gljivičnih patogena uključuju upotrebu ekološki prihvatljivih i manje toksičnih spojeva, među koje potencijalno spadaju boronske kiseline. Pokusom in vitro istražen je antimikotički učinak fenilboronske i borne kiseline na gljivu A. alternata. Nakon izolacije patogena iz rajčice, određena je minimalna inhibitorna koncentracija fenilboronske i borne kiseline za rast micelija primjenom tehnike poisoned food. Antimikotički učinak testiran je na širokom rasponu koncentracija fenilboronske i borne kiseline (od 0,04 % do 0,3 %), pojedinačno umiješanih u hranjivu podlogu na kojima je tijekom petodnevne inkubacije uzgajan micelarni disk kulture patogena. Fenilboronska je kiselina pri niskoj koncentraciji (0,05 %) potpuno inhibirala rast micelija. Primjena borne kiseline u različitom rasponu koncentracija nije značajno umanjila rast micelija, ali je primijećeno smanjenje sporulacije patogena, čime se potvrđuje fungistatski učinak borne kiseline. Prema našoj spoznaji, ovo je prva studija koja opisuje in vitro antimikotički učinak fenilboronske kiseline na patogen koji je važan u poljoprivredi. Štoviše, s obzirom na to da je A. alternata i patogen ljudi, studija ima i potencijalni medicinski značaj.