Efficiency of antifungal compounds against powdery mildew disease of rose (Podosphaera pannosa)

Abstract

© 2020 Association of Agricultural Technology in Southeast Asia. All rights reserved. The Powdery mildew on rose caused by the fungus Podosphaera pannosa is a serious problem in comercial rose garden. All aerial parts of the plant can be infected with the production of white mycelium containing conidiospores. Conidiospores can be dispersed by wind or rain to healthy plants. Infection is promoted by high humidity or where poor air movement occur in dryer environments. In this experiment, we observed a rose powdery mildew that was found in rose cultivar “Queen Sirikit” using a light microscope. The morphological characteristics of the anamorph revealed mycelium with indistinct or nipple-shaped appressoria, conidia with fibrosin bodies that measured approximately 6 to 8 x 17 to18 μm and fuliginea-type germtubes. Conidiophores were straight, ca. 5 to 7 x 41 to 80 μm with cylindrical foot-cells. The efficacy of antifungal compounds salicylic acid (SA), fresh cow’s milk (10%/V.) and some biocontrol agents: the bacterium Bacillus subtilis (BS) and the hyperparasitic fungus Ampelomyces sp. were compared with the conventional fungicide carbendazim using an onion tissue bioassay. The results showed that SA inhibited conidia germination by 99.72% followed by BS (98.99%), Ampelomyces sp. (95.41%), carbendazim (83.24%) and the last was fresh cow’s milk by 80.81%. The control treatment had 100% spore germination. The potential of the antifungal compounds was assessed in a greenhouse experiment and SA was a superior treatment to reduce the severity of disease (57.78%).