Nematode community study in a germplasm bank of representative olive cultivarsfrom the Mediterranean basin

Abstract: Olive is a key crop, both economically and socially in southern Spain. Although theinteraction of plant-parasitic nematodes with free-living nematodes could play an important rolein their control, it is not known how the olive genotypes may influence the rhizosphereenvironment and consequently the balance between plant-parasitic and free-living nematodes.The aim of this work was to study the nematode communities associated with rhizospheric soiland roots of a collection of 16 olive cultivars from a world olive germplasm bank at southernSpain and assess whether olive genotype determine differences in the nematofauna present intheir rhizosphere. Classical nematological analysis, including soil nematode extraction, speciescounting and morphological identification was performed. In addition, total soil DNA wasextracted from the same samples and used for analysis of genetic diversity of total nematodepopulations using Terminal Restriction Fragments Length Polymorphism (T-RFLPs) analysis ofthe 18S rDNA gene. Results showed that 24 taxa belonging to 8 genera (includingCriconemoides, Ditylenchus, Filenchus, Helicotylenchus, Merlinius, Paratylenchus, Tylenchus,and Xiphinema) and 8 families (including Aphelenchidae, Belonolaimidae, Criconematoidae,Hoplolaimidae, Longidoridae, Sphaerularioidea, Tylenchidae and Tylenchulidae) of plantparasiticnematodes were present, with one species (Helicotylenchus digonicus) being prevalentin all samples. There was no clear relationship between incidence or population density of eachnematode species with the olive genotype. General nematode maturity index (MI) values wereinconsistent between olive varieties and did not therefore distinguish differences in the levels ofsoil disturbance. However, plant-parasitic nematode index (PPI) was significantly modified byolive variety within the single field. In addition, T-RFLP analysis showed differences betweenolive cultivars, with samples associated with specific varieties showing higher diversity ofnematode taxa.