Effect of propolis extract on Zucchini yellow mosaic virus inhibition in oilseed pumpkin

Abstract

Propolis, the mixture of the nectar of flowers collected by honeybees, showed antiviral activity against human and plant viruses. Since Zucchini yellow mosaic virus (ZYMV, Potyvirus, Potyviridae) is the most important pathogen of oilseed pumpkin (Cucurbita pepo var. styriaca) production worldwide, the aim of this study was to evaluate the effect of propolis extract on ZYMV infection in oilseed pumpkin. Propolis extracted by 95% ethanol was diluted in distilled water to concentration of 1, 2.5, 5 and 10%. Effects of different propolis concentration were evaluated in in vitro and in vivo experiments. In vitro, ZYMV inoculum was mixed with different propolis concentrations and oilseed pumpkin plants were inoculated immediately, 1 and 2 hours after mixing. In vivo, oilseed pumpkin plants were sprayed with different propolis concentrations before and after ZYMV inoculation immediately, 1 and 2 h later. In each experiment 10 oilseed pumpkin plants in one true leaf stage were inoculated. Plants inoculated with ZYMV and sprayed with propolis were used as a positive and negative control, respectively. Symptom appearance was checked 10 days post-inoculation. Only 5 and 10% propolis concentration showed effect in reducing symptoms of ZYMV infection, in all experiments. In vitro, number of symptomatic plants was reduced to 80 and 70% after one-hour period, and to 70 and 60% after two-hour period. In vivo, propolis concentrations of 5 and 10% sprayed before inoculation reduced number of symptomatic plants to 70 and 60% after one-hour period, and to 60 and 50% after two-hour period, while concentrations of 5 and 10% sprayed after inoculation, reduced number of symptomatic plants to 80% each after one-hour period, and to 70 and 80% after two-hour period. In this study propolis exhibited a positive effect on reduction of ZYMV infection despite the fact that plants were challenged with higher levels of the virus than it occurs naturally. Encouraging results of propolis capacity for direct virus control should be confirmed in the field under natural conditions.