Biological Control of Powdery Mildew on Zinnia (Zinnia elegans, L) Using Some Biocontrol Agents and Plant Extracts

Abstract

Powdery mildew is a potentially serious disease of Zinnia (Zinnia elegans). The disease is caused by the airborne fungus Erysiphe cichoracearum and it is an occasional disease of Zinnia in Egypt. Culture filtrates of Trichoderma harzianum, Epicoccum sp., Streptomyces endus and an actenomycetal isolate in addition to two plant extracts i.e. miswak (Salvadora persica) and henna (Lawsonia inermis) were evaluated to control powdery mildew disease of Zinnia plants. Culture filtrates of the aforementioned biocontrol agents were used as 25 and 50%. Bioassays were conducted under field conditions during the two successive seasons of 2006 and 2007 at the Experimental Farm of the Fac. of Agric., Kafr El-Sheikh Univ., Egypt to test the efficacy of these culture filtrates applied to protect Zinnia plants from powdery mildew disease. Spraying zinnia plants four times, beginning from June 15 th with one week interval by a hand atomizer under field conditions with the previously culture filtrates and the two plant extracts gave sufficient control to powdery mildew disease. The obtained results showed that, all used treatments led to significant decrease in both disease incidence and severity compared with control treatment. The highest disease incidence inhibition was obtained when Epicoccum sp. and T. harzianum were used as 50% (v/v) sterilized water followed by henna and miswak extracts were used, respectively. Sprayed plants recorded best results for most growth characters, peroxidase (POX) and polyphenol oxidase (PPO) enzymes activity compared unsprayed one. In conclusion, biocontrol agents and some plant extracts can be substitutes to fungicides as an alternative and safe method for controlling powdery mildew disease of Zinnia.