Influential Cooperation between Zeolite and PGPR on Yield and Antimicrobial Activity of Thyme Essential Oil

Aims: To study the interaction effect among the natural substance (zeolite), plant growth promoting rhizobacteria (PGPR) and Saccharomyces cerevisiae extract as foliar spraying on vegetative growth characteristics, yield and essential oil properties as well as chemical composition of its hydrodistilled essential oils by GC were studied. Also, microbial enzymes activity in thyme’s rhizosphere and the antimicrobial activity of the essential oil extracts was evaluated against some pathogenic microorganisms.

Methodology: During two successive seasons 2013-2014 and 2014-2015, two field split plot experiments were conducted at the Experimental Farm of Horticulture Dep., Fac. Agric. Benha Univ. The present study include two foliar spraying treatments in the main plot (without and with Saccharomyces cerevisiae extract) and five treatments in the sub plot (control, full dose of NPK, half dose of NPK + PGPR , full dose of zeolite, half dose Zeolite + PGPR).PGPR namely Azotobacter chrococcum ML1, Bacillus circulans ML2 and Bacillus megaterium ML3. Vegetative growth characteristics (plant height, branches number, fresh and dry weight), yield and essential oil properties and chemical composition of its hydrodistilled essential oils by GC were studied. Also, microbial enzymes activity (dehydrogenase, phosphatase and nitrogenase) in thyme’s rhizosphere and the antimicrobial activity (minimum inhibitory concentration) of the essential oil extracts was evaluated against some pathogenic microorganisms viz., Salmonella typhorium, Pseudomonas aureogenosa, Staphylococcus aureus, Bacillus cereus and Candida albicans.

Results: Results indicated that thyme’s rhizosphere amended with half dose of zeolite combined with PGPR and Saccharomyces extract gave the highest significant values of all estimated enzymes. In addition, plant height, branches number/plant, fresh and dry weights were higher in plants inoculated with PGPR combined with zeolite at half dose and sprayed with Saccharomyces extract compared with other treatments. These results are true in two cuts and in both two growing seasons. On the other hand, chemical analysis of thyme grown under different treatments showed that chemical fertilizer treatments gave the highest significant values of macronutrients and carbohydrates content. Regarding the effect of different treatments on essential oil composition of Thymus vulgaris, it was clearly that the main components were thymol, β-phyllandrene and myrcene. These components of thyme’s oil were able to inhibit all tested pathogens via minimum inhibitory concentration (MIC) test which resulted that the examined Gram positive bacteria were more sensitive rather than either Gram negative or Candida albicans.