Native mycorrhizal communities of olive tree roots as affected by protective green cover and soil tillage

Arbuscular mycorrhizal fungi (AMF) are beneficial symbionts associated with the roots of most food crops and improve plant nutrient uptake and tolerance to biotic and abiotic stresses. AMF implementation in food production requires targeted studies on the factors affecting their development in differently managed agroeco-systems. Here, we investigated the diversity and community composition of native AMF in the roots of olive trees, as affected by a long-term permanent green cover and shallow tillage, at two different soil depths, in a high-density olive orchard under Mediterranean climate conditions, by using a molecular approach, PCR-denaturating gradient gel electrophoresis (PCR-DGGE) of partial 18S rRNA gene. Olive root colonization was 20-30%. Analysis of similarities (ANOSIM) of PCR-DGGE clusters revealed significant differences in AMF community composition of olive tree root samples collected from permanent cover versus tillage treatment. The DGGE bands, excised, sequenced and affiliated to AMF species using Basic Local Alignment Search Tool and phylogenetic trees analyses, allowed, for the first time, the identification of native mycorrhizal microbiota colonizing olive tree roots. This is the first work showing that two different managements of olive orchard floor permanent green cover versus shallow tillage - are able to shape AMF community composition in olive tree roots, regardless of soil depth. Moreover, the finding that most sequences retrieved from olive tree roots (86%) were affiliated to sequences of forest and fruit trees represents an excellent clue for studying host preference of specific AMF for trees, also in relation to their functional significance, in the years to come.