Entomopathogenic nematode natural distribution in vineyards managed with cover crops: impact on activity and soil organisms' assemblage

Abstract

Viticulture is a worldwide valuable sector, with special relevance in Spain for their socio-economic impact. Vineyards are threatened by numerous pests and diseases, and their management relies primarily on use of conventional agrochemicals. Current paradigm of sustainability pursues the implementation of ecologically sound strategies. The use of cover crops is arising as an alternative with numerous benefits, including favouring above-belowground biodiversity. We hypothesize that vineyard with cover crops might increase the prevalence of entomopathogenic nematodes (EPNs), biocontrol agents of soil pests, modulating the assemblage of other associated organisms. The presence and activity of native EPNs were evaluated in an ongoing experiment in La Grajera (Logroño, Spain) on Vitis vinifera var Tempranillo (clon RJ-26, rootstock “110-Richter”) investigating tillage, and three types of covers: spontaneous, flower-driven, and seeded with Bromus perenne (Poaceae) (n = 3 per treatment). During late-spring and early-autumn 2017, 48 composite soil samples (12 cores, 2.5 cm diam X 20 cm depth) were taken to ensure balanced spatial distribution (two pair’s rows/inter-rows per plot). Each sample was assessed for the presence and abundance of 9 EPNs and other related organisms: 6 nematophagous fungi, 5 free-living nematodes (FLNs), and 2 ectoparasitic bacteria, by qPCR approaches. Moreover, traditional insect-bait provided the measurement of EPN activity. In spring 2017, nematode activity was slightly higher (P = 0.068) in inter-rows than in rows. However, this trend was only observed for the tillage and seeded treatments in later autumn (P < 0.05). Two EPN species were isolated: Steinernema feltiae and, for the first time in La Rioja, Heterorhabditis bacteriophora. The insect-baits detected low EPN-FLN incidence in the isolates, indicating that EPNs could suffer low competition with other nematodes for the cadaver under this scenario. The ongoing surveys in 2018 will supply additional data on their natural distribution and assemblage.