Trend to explain the distribution of root-knot nematodes Meloidogyne spp. associated with olive trees in Morocco

•First root-knot nematode survey done in olive growing areas in Morocco.•Dispersion of Meloidogyne species due to human activities and crop intensification.•Some species (including new ones) persistent on wild olive in LGM plant refuges.•Common species M. javanica widespread in olive orchards.•Dispersion of this species supposed to be related to introductions from nurseries.

Knowing which factors affect the distribution of organisms provides useful insights for the management of biodiversity. For root-knot nematodes Meloidogyne (RKN), a critical threat in agriculture, an understanding of the constraints that impact their diversity is a fundamental prerequisite for their control. RKN are reported to be major pests on olive trees, mainly in high-density orchards and in nurseries. This study was undertaken in order to characterise the Meloidogyne species associated with olive trees in Morocco and to consider how anthropogenic stresses and some edaphic and climatic factors may be involved in their spatial distribution. A soil sampling was conducted in the main olive growing areas in Morocco, including wild, feral and cultivated olive trees. RKN were detected in 12.2% of the samples. The analysis of biochemical (esterase patterns) and molecular (SCARs, D2D3) markers revealed the occurrence of M. javanica (as the predominant species), M. arenaria, M. hapla, M. spartelensis and of an undescribed species Meloidogyne n.sp. Some esterase variability was detected in M. javanica and M. hapla populations. The RKN species were distributed everywhere on an aggregated basis. However, M. javanica was recorded in high abundance throughout the cultivated areas in Morocco in high-density and traditionally cultivated olive orchards and rarely on some feral olive, while the other species were detected in low abundance on wild olive in mountain plant refuge areas in northern and southern Morocco. Nevertheless, the large distribution of M. javanica in cultivated areas could be primarily due to widespread introductions from nurseries, followed by multiple founder processes favoured by local conditions such as irrigation and planting density. In contrast, the detection of the other species hosted by wild olive only in plant refuge areas suggest that these areas host ancestral nematode species that did not disperse in the absence of human activities.