Endemic Atlantic Forest species of Caryophyllales as inhibitors of viral infection in zucchini

Abstract

In Brazil, zucchini (Cucurbita pepo) is a socioeconomically important vegetable affected by damage caused primarily by zucchini yellow mosaic virus (ZYMV). Although the occurrence of cucumber mosaic virus (CMV) is less frequent, in C. pepo ‘Caserta’ plants it can cause symptoms such as mottle, mosaic, leaf and fruit distortion, as well as reduced plant development. To minimize the damage, the most widely used management technique is the preventive, albeit inefficient, application of insecticides, aimed at controlling aphids, the vectors of this virus. Thus, the search for more effective and less environmentally harmful control methods has been the target of investigations. The purpose of the present study was to assess the action of the extracts of four native Caryophyllales species, as inhibitors of infection by CMV and ZYMV in C. pepo, in addition to evaluating the possible induced resistance in this species. Fresh leaf extracts (LEs) of Guapira opposita, Pisonia ambigua (Nyctaginaceae), Gallesia integrifolia and Seguieria langsdorffii (Phytolaccaceae), previously assessed in the tobacco mosaic virus / Nicotiana glutinosa pathosystem, were submitted to progressive dilutions sprayed on cotyledonary C. pepo leaves 30 min before inoculation with CMV and ZYMV. Leaf extracts of G. integrifolia did not induce inhibition in any of the pathosystems assessed. Guapira opposita LEs inhibited the infection of plants inoculated with ZYMV below 50% but inhibited CMV infection by 70% at a concentration of 1:40. Given that leaf extracts of P. ambigua and S. langsdorffii induced high percentage inhibition, evident in the number of asymptomatic plants and confirmed by serological tests, these species were selected to assess induced resistance in pre-treatment experiments. The LEs were efficient in inhibiting ZYMV and CMV infection in C. pepo when applied up to 48 h before inoculation. The LEs of S. langsdorffii and G. opposita, also tested for this system, were efficient when applied up to 72 h before CMV inoculation. The LEs can be prepared from dry leaves and maintained at -20°C for at least three years, conserving their inhibitory activity. These results expand the possibilities for producers and consumers alike in the sustainable management of the main zucchini viruses, without damaging the environment.