Bioprospecting for plant and fungus extracts with systemic effect to control the cucumber powdery mildew.

This work was aimed to select plant and fungus extracts showing systemic effect to control the cucumber powdery mildew. For that, ethanolic extracts were obtained from five basidiomycetes and 71 plant species and tested under greenhouse conditions. Cucumber plants cv. 'Safira' were sprayed with extracts at the first true leaf growth stage and inoculated with Sphaerotheca fuliginea at the second leaf growth stage. The number, diameter and sporulation rate of powdery mildew colonies were evaluated 6 days after inoculation. In an initial screening phase, the extracts of the following plants and fungi revealed some systemic effect against the powdery mildew: Aloe vera (aloe), Bidens pilosa, Ganoderma sp. (basidiomycete), Hyptis crenata, Mascagania betbamiana, Ocotea suaveolens, Oudemansiella canarii (basidiomycete), Pinus taeda (pine), Riehardia grandiflora and Vernonia polyanthes. They were compared in three other experiments and those from Oudemansiella, Ganoderma, pine needles and aloe leaves were the most efficient reducing the number of colonies on the secondary leaf by 79, 65, 30 and 21 %, respectively. Extracts from fruiting bodies of Oudemansiella and Ganoderma also decreased the diameter of colonies by 20 % as well as the sporulation rate by 45 and 70 %, respectively. While Ganoderma did not show any direct effect in vitro, the extract of Oudemansiella (60 mg fresh weight ml[-1]) reduced the germination of powdery mildew conidia at 48 h after inoculation by 71 %. Furthermore, Oudemansiella-extract strongly inhibited the mycelium growth of Cladosporium oxysporum in liquid medium. The possible modes of action of these extracts are discussed