Leaf and powdery mildew colonization by glycolipid-producing Pseudozyma species

In this work, we followed the development and compared the biocontrol potential of four phylogenetically related species of Pseudozyma (P. antarctica, P. flocculosa, P. fusiformata and P. rugulosa) all known to release glycolipids with antifungal activity in vitro. To this end, we developed GFP transformants and specific primers for each species and conducted in situ observations and quantification of their population sizes over time on both healthy and powdery mildew-infected leaves. Although all species shared many similar features, only P. flocculosa antagonized powdery mildew colonies and grew specifically in their presence. Population quantification by qRT-PCR following inundative applications showed a drastic decline in population for all species, including P. flocculosa on healthy leaves, but a sharp and steady increase of the latter over 72 h on infected leaves. These results suggest that production of glycolipids, and more specifically flocculosin or ustilagic acid, is not the sole factor dictating biocontrol activity among Pseudozyma spp.