Antiphytoviral Activity of the Plectranthus tenuiflorus on Some Important Viruses

Crude extract of Plectranthus tenuiflorus crude extract was tested as an antiphytoviral agent against different plant viruses like Tobacco Necrosis Virus (TNV), Tobacco Mosaic Virus (TMV), and Tomato Spotted Wilt Virus (TSWV). When it was applied onto Phaseolus vulgaris, Datura stramonium, and Chenopodium amaranticolor as pre-inoculation spray (in vivo), it reduced the infectivity of above viruses by 90.6, 85.8 and 77.7%, respectively. However, when the extract was mixed with the virus inoculum (in vitro), it inhibited the local lesion development by 100% after one hour of mixing for TNV, and three hours for both TMV and TSWV. Effect of P. tenuiflorus on the systemic TMV infection was also studied. It delayed the onset of the disease development from 4 to 5 days, although it had less apparent effect on the virus accumulation. Studying the effect of temperature and rate of dilution on the antiphytoviral activity revealed that the thermostable property of this extract as well as remaining of its antiphytoviral activity up to 10 dilution rate. In order to investigate the bioactive constituent of the P. tenuiflorus. Crude extract, its proteins, carbohydrates, and storage oil were separated and tested as an antiphytoviral agent. The results indicated that the antiviral activity was not mainly attributed to these constituents.