Learning from olive evolution and cultivation to understand the diversity of associated plant-parasitic nematodes communities in Morocco

Plant-parasitic nematodes (PPN) significantly contribute to economic losses in the top-tenolive producing countries, especially in the Mediterranean basin. Instead of controlling themain pathogenic nematode species as usual, one innovative strategy to control PPN would beto manage diversity in communities in order to lead them to be less pathogenic. Then,knowing assemblage mechanisms in communities due to evolution and environmental forcesis a prerequisite. This study was conducted in Morocco, because (i) information about PPNdiversity is lacking, (ii) different forms of olive occur as wild (including two sub species O.europaea subsp. europaea and subsp. Maroccana), feral and typical cropping systems astraditional and high density and as irrigated or not) are present. Morphobiometric observationsrevealed a very diverse parasite nematofauna (117 species), seven new taxa being recorded forthe first time on olive. Tylenchidae, Hoplolaimidae and Telotylenchidae nematodes weredominant (80% of the samples), whereas root-knot nematodes (Meloidogyne spp.) weredetected in 40% of the samples. Multivariate analyzes showed that the development ofHeteroderidae and Longidoridae nematodes was favored in PPN communities on wild olive,while lesion (Pratylenchidae) and root-knot nematodes multiply in orchards. ThreeMeloidogyne species were identified: M. javanica on feral and cultivated olive in southern andcenter Morocco; M. arenaria and M. hapla on wild olive in the north. Cytochrome oxidase I(COI) and Internal transcribed spacer-2 (ITS2) genes were good markers for speciesdifferentiation, but they were not able to distinguish M. javanica and M. arenaria populationsand were not adapted for intraspecific differentiation. However, a significant morphologicalvariability was observed between the Meloidogyne species, and within and between M.javanica populations. The response of the diversity of PPN communities as well as ofMeloidogyne populations to olive genotype, geo-climatic zones and soil physico-chemicalcharacteristics, and diversity of plants associated with olive trees is discussed.