Organic viticulture enhanced the activity of native entomopathogenic nematodes in DOCa Rioja soils (North of Spain)

Abstract

Vineyards and their associated socio-economic activities are relevant sectors worldwide. Still, this agroecosystem is one of the most intensely managed crops and erosion-prone land areas. The conventional viticulture practices to control pests, diseases, and weeds, like tillage and agrochemical applications, accelerate the loss of soil biodiversity and compromise the presence of beneficial soil organisms such as the entomopathogenic nematodes (EPNs). Such human disturbances in the agroecosystems can strongly affect abiotic (e.g., soil texture and properties) and biotic factors (natural enemies and potential competitors) that modulate the EPN activity as biological control agents. For the first time in viticulture, this study aimed to investigate the impact of differentiating management on the EPN community and associated soil organisms and if their assemblage will provide indicators of better practices for sustainable farming. We hypothesized that organic pest management and alternative strategies to tillage might enhance the abundance and activity of the native EPN community in vineyard soils. In autumn 2019, we collected two composite soil samples from 80 vineyards distributed across the Guaranteed Designation of Origin (denominated DOCa) Rioja region. The sites belonged to one category of each of the two factors: pest management (integrated vs. organic, 40 plots each) and soil managing (tillage vs. cover cropping, 48 and 32 vineyards, respectively). Isolated through sucrose-gradient centrifugation and employing species-specific primers/probe qPCR sets, we investigated the presence of ten EPN species and associated soil organisms: four free-living nematodes (FLNs), six nematophagous fungi (NF), and two ectoparasitic bacteria (EcPB). Besides, we estimated the EPN activity using the traditional insect-bait method. We included in the analysis twenty soil variables to characterize the evaluated treatments and assess their impact on soil organism distribution. Our results provide evidence on the support of organic viticulture to beneficial soil organisms, notably the activity of native EPNs. We also reported a higher abundance of S. feltiae (the predominant steinernematid species in Europe) and FLNs for organic farming than IMP, while the presence of NF and EcPB resulted in unaffected. Contrarily, the soil management practices considered did not differ in their impact on EPNs or their natural enemies/competitors, even if contrasted for several soil properties. Future research may expand the screened soil-dwelling species using novel molecular technics to unravel their complex interactions and determine the best farming practices to preserve soil health.