Impact of vineyard ground cover management on the occurrence and activity of entomopathogenic nematodes and associated soil organisms

Viticulture is a valuable sector worldwide with an extraordinary socio-economic impact in Spain. Numerous pests and diseases threaten vineyards, and their management primarily relies on the use of conventional agrochemicals. The current paradigm of sustainability pursues the implementation of ecologically sound strategies in vineyard ecosystems. The use of cover crops is arising as an alternative with numerous benefits, including favoring above-belowground biodiversity and the presence of beneficial soil organisms such as the entomopathogenic nematodes (EPNs). We hypothesized that the use of specific cover crops in vineyards might enhance the natural occurrence and activity of EPNs by modulating the assemblage with associated organisms. We performed the experiments in an ongoing experimental vineyard (Vitis vinifera var Tempranillo, clon RJ-26, rootstock ‘110-Richter’) located in Logroño (Spain), drove with different soil management systems (three replicates each): conventional tillage practice and the cover crops (i) seeded with Bromus catharticus (Poaceae), (ii) flower-driven, and (iii) spontaneous. We took four soil composite samples per plot (n = 48 per sampling time) late spring and early autumn in two consecutive years (2017 and 2018). By using species-specific primers/probes qPCR sets, we screened for the presence and abundance of eight EPNs species and 12 related soil organisms: six nematophagous fungi, four free-living nematodes, and two ectoparasitic bacteria. Additionally, we assessed the EPN activity by the traditional insect-bait method. Overall, we recorded higher EPN numbers or activity rates on cover crops than on bare soils. However, some of the results were divergent among no-till treatments. We observed not only higher EPN abundance and activity on spontaneous covers but lower numbers of antagonistic organisms, particularly endoparasitic nematophagous fungi. Thus, according to our results, the use of spontaneous covers could be the most promising strategy to support the conservation biological control service provided by the naturally occurring EPN species in vineyards, plus with a low cost for the sector.