Evaluation of the effect of an organic biostimulant on ZYMV transmission and infection in Cucurbita pepo L.

Biostimulants are fertilizers whose function is to stimulate nutrition process of the plants by improving plant and/or rhizosphere characteristics. The effect of a biostimulant containing alfalfa, brown algae, and molasses extracts on the interaction between zucchini (Cucurbita pepo) and zucchini yellow mosaic virus (ZYMV) was evaluated. ZYMV is an aphid-transmissible potyvirus that affect several crops and weeds worldwide. We compared plants which were treated or untreated with biostimulant, looking at healthy and ZYMV-infected plants. ZYMV titre and defence gene expression level (seven from systemic acquired resistance, one from pattern-triggered immunity and three from oxidative stress pathway) were quantified using qPCR. Viral symptoms and plant growth parameters (number of leaves, flowers and fruits) were also recorded. Preliminary data showed that biostimulant-treated plants exhibited an increased growth and upregulation of plant defence genes, both in healthy and ZYMV-infected conditions. Virus titre was also reduced in biostimulant-treated plants compared to untreated plants. We further investigated the biostimulant influence on the settling preference of the aphid vector of ZYMV, Aphis gossypii. Aphid choice test experiments using detached zucchini leaves showed that fewer A. gossypii specimens settled on biostimulant-treated plants, with and without ZYMV. Volatile organic compounds (VOC) produced by these plants and the potential effects of VOC on aphid choice are under study (olfactometer experiments) to tests if the biostimulant not only boosts plant growth but also increases resistance to aphids and the diseases they transmit.