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 nippleshaped
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%).
Keywords
rose powdery mildew, Podosphaera pannosa, salicylic acid, Bacillus subtilis, Ampelomyces sp., Biological control
INTERNATIONAL JOURNAL OF AGRICULTURAL TECHNOLOGY
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