Essential oils from some Egyptian aromatic plants as an antimicrobial agent and for prevention of potato virus Y transmission by aphids

Essential oils from different Egyptian aromatic plants (Mentha piperita, Ocimum basilicum, and Thymus vulgaris) were tested for their inhibitory effect on some selected harmful bacteria and yeast (Escerichia coli, Psedumonas aeruginosa, Staphylococcus aureus, Streptococcus pyogenes, and Candida albicans). Aerial parts from plants were directed to steam distillation for essential oil extraction. Oil yields were expressed in relation to dry weight of plant material, which found to be 0.39%, 0.20% and 0.55% w/w for M. piperita, O. basilicum and T. vulgaris, respectively. The types and percentage of essential oil constituents were determined using gas chromatography (GC). GC data revealed that the main compounds from M. piperita were menthol (35.44%) and menthone (20.11%), O. basilicum main component was linalool (45.11%), while T. vulgaris oil main component was thymol (75.76%). Preparations studied for their inhibitory effect were raw oils for sensitivity test and in the form of emulsions for spraying application. Emulsions were prepared depending on commercial liquid dish wash soap (Peril®) and Tween 80 as emulsifying agents. Results of sensitivity tests indicated that the most effective oil against bacteria and yeast was that of O. basilicum followed by that of T. vulgaris. O. basilicum oil was highly effective on S. pyogenes giving a zone of 19 mm more than that produced by Ampicillin, which was of 15 mm in diameter. Oil of O. basilicum was slightly more effective on C. albicans when compared with clotrimazole as an antifungal agent. Spraying potato tubers with O. basilicum oil emulsified with soap prior to brown rot bacteria (Ralstonia solanacearum) infection and preservation at 4 °C gave the best results followed by T. vulgaris oil with soap, as only 2 and 3 tubers out of 10 used shows rot symptoms, for O. basilicum and T. vulgaris oils, respectively. After feeding Myzus persicae aphids on potato virus y potyvirus (common strain) (PVYO) infected tobacco plants for 1 h, insects were print-captured individually and virus was successfully detected by immunocapture reverse transcriptase polymerase chain reaction PC/IC-RT-PCR, as the 801 bp coat protein gene (cp) bands were detected within agarose gel. Spraying tobacco plants with O. basilicum or T. vulgaris oils both emulsified with soap gave excellent results, as 8 and 6 plants out of 10 treated confirmed to be PVYO-free by giving negative I-ELISA results, respectively. It was also observed that adding soap as an emulsifier has a killing effect on aphids.