Bacillus subtilis as a bio-agent combined with nano molecules can control powdery mildew disease through histochemical and physiobiochemical changes in cucumber plants.

The effect of bio-agent Bacillus subtilus , nano titanium dioxide (TiO 2) and Zinc oxide (ZnO) as well as the combination compared with fungicide (Topas100) was investigated under laboratory (in vitro) and greenhouse conditions against powdery mildew disease caused by Podosphaera xanthi i. Most of treatments were strong to inhibit the spore germination of P. xanthii. B. subtilus and B. subtilus + nano-Tio 2 were the most effective followed by Topas100, B. subtilus + nano-ZnO, nano-ZnO and Nano-TiO 2 compared with control. Most of treatments significantly reduced the disease symptoms and diseases severity (%) particularly bio-agent, nano-ZnO and combination of B. subtilus + nano-ZnO, however, the fungicide treatment showed the best inhibition. As a consequence of treatments histo-biochemical and growth parameters of cucumber were changed. Reactive oxygen species (hydrogen peroxide and superoxide) were accumulated early. Chlorophyll content, catalase, peroxidase, and polyphenol oxidase activities were increased under various treatments, however, electrolyte leakage (EL) was decreased. The growth characters e.g. plant height, leaves number, fresh and dry weight/plant was significantly improved because of treatments. Combined of B. subtilus and nano-Zinc oxide treatment was the best treatment and promising to be an alternative to fungicide, consequently, decreasing the environmental pollution, cost and harmful effect of fungicide on human health. • Application of Bacillus subtilus as bio-agent led to improve cucumber plants under powdery mildew disease. • Combination of B. subtilus and nano-Zinc oxide treatment give the best results and promising to be an alternative to fungicide. • Hydrogen peroxide, superoxide and electrolyte leakage (EL) were decreased, however chlorophyll content and fruits yield were increased with B. subtilus + nano-Zinc. [ABSTRACT FROM AUTHOR]