How anthropogenic changes may affect soil-borne parasite diversity? Plant-parasitic nematode communities associated with olive trees in Morocco as a case study

Abstract

BackgroundPlant-parasitic nematodes (PPN) are major crop pests. On olive (Olea europaea), they significantly contribute to economic losses in the top-ten olive producing countries in the world especially in nurseries and under cropping intensification. The diversity and the structure of PPN communities respond to environmental and anthropogenic forces. The olive tree is a good host plant model to understand the impact of such forces on PPN diversity since it grows according to different modalities (wild, feral and cultivated olives). A wide soil survey was conducted in several olive-growing regions in Morocco. The taxonomical and the functional diversity as well as the structures of PPN communities were described and then compared between non-cultivated (wild and feral forms) and cultivated (traditional and high-density olive cultivation) olives.ResultsA high diversity of PPN with the detection of 117 species and 47 genera was revealed. Some taxa were recorded for the first time on olive trees worldwide and new species were also identified. Anthropogenic factors (wild vs cultivated conditions) strongly impacted the PPN diversity and the functional composition of communities because the species richness, the local diversity and the evenness of communities significantly decreased and the abundance of nematodes significantly increased in high-density conditions. Furthermore, these conditions exhibited many more obligate and colonizer PPN and less persister PPN compared to non-cultivated conditions. Taxonomical structures of communities were also impacted: genera such as Xiphinema spp. and Heterodera spp. were dominant in wild olive, whereas harmful taxa such as Meloidogyne spp. were especially enhanced in high-density orchards.ConclusionsOlive anthropogenic practices reduce the PPN diversity in communities and lead to changes of the community structures with the development of some damaging nematodes. The study underlined the PPN diversity as a relevant indicator to assess community pathogenicity. That could be taken into account in order to design control strategies based on community rearrangements and interactions between species instead of reducing the most pathogenic species.

Adaptive response to olive cultivation in a generalist parasitic nematode (Meloidogyne javanica)

“…In this study, we worked on the 17 Moroccan populations of the nematode Meloidogyne javanica that were sampled in olive stands by Ali et al (2016Ali et al ( , 2017. Even if this species is parasiting the roots, we collected soil in the upper rhizosphere (the 20-30 cm deep) with a small spade (Ali et al, 2016(Ali et al, , 2017, because M. javanica spend almost all of their life cycle in the soil (Cadet & Thioulouse, 1998). This nematode survey was carried out from March to April 2012.…”

“…S1. We reused the same population labels as described in Ali et al (2017). Those populations were either collected on cultivated olives or oleasters, to which we will then refer as "Cultivated" and "Wild" habitat, respectively [see Ali et al (2017) for more details on sampling locations].…”

“…We reused the same population labels as described in Ali et al (2017). Those populations were either collected on cultivated olives or oleasters, to which we will then refer as "Cultivated" and "Wild" habitat, respectively [see Ali et al (2017) for more details on sampling locations]. Cultivated olives from the agricultural sites correspond to the 'Picholine Marocaine' cultivar (Ali et al, 2017), that is largely spread in Morocco (Khadari et al, 2008), but we did not have any information about rootstock genotypes.…”

“…Those populations were either collected on cultivated olives or oleasters, to which we will then refer as "Cultivated" and "Wild" habitat, respectively [see Ali et al (2017) for more details on sampling locations]. Cultivated olives from the agricultural sites correspond to the 'Picholine Marocaine' cultivar (Ali et al, 2017), that is largely spread in Morocco (Khadari et al, 2008), but we did not have any information about rootstock genotypes. All cultivated olives were conducted in traditional (7 locations) and F o r P e e r R e v i e w 6 high density orchards (5 locations; Ali et al, 2017).…”

“…The structure of microbiome communities associated to the olive still needs to be better investigated to assess the impact of olive domestication and cultivation practices on their diversity (Besnard et al, 2018). Recent studies on nematodes (Palomares-Rius et al, 2012, 2015Ali et al, 2017;Archidona-Yuste et al, 2018, 2020a and fungi (Montes-Borrego et al, 2014;Abdelfattah et al, 2015) associated to the cultivated and/or wild olives indicate that such communities are influenced by environmental factors (e.g. soil parameters, cultivation methods) but also the genotype of the host.…”