Abstract

The utilization of yeasts as bio-control agents against fruit pathogens may represent an effective alternative to the use of synthetic chemical fungicides. Recently, Giobbe et al. (2007) reported the case of the dimorphic yeast Pichia fermentans that is able to control brown rot caused by Monilia spp. on apple fruits but causes a rapid fruit decay and shows a pathogenic behaviour when tested on peaches. Interestingly, in both cases P. fermentans forms biofilm on fruit surfaces, but this is made of yeast-like cells on apple and pseudo-hyphae on peach fruits. In this context, it seems crucial to understand whether the pathogenic behaviour of P. fermentans is a consequence of pseudohyphal growth and, therefore, if the ability to form pseudo-hyphae is one of the risk factors to be evaluated in view of the utilization of microbial antagonists. In the present work, with the aim of elucidating the mechanisms involved in P. fermentans dimorphic transition, we looked for the nutritional conditions able to induce and separate yeast-like and pseudo-hyphal growth. While on urea-containing medium P. fermentans produces a biofilm made of yeast-like cells, on methionin, as the sole nitrogen source, the biofim consists merely of pseudohyphae. The role of methionin on filamentation will be discussed.

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