Molecular and agronomic responses to soil inoculation with plant-growth promoting rhizobacteria and arbuscular mycorrhizae in Triticum durum

Abstract

Plant-growth promoting rhizobacteria (PGPR) and arbuscular mycorrhizal (AM) fungi contribute to plant nutrient uptake by increasing the availability of nutrients and the root adsorbing surface. However, the molecular mechanisms of plant responses to these associations are still under-investigated. Gene expression analysis could lead to the identification of biomarkers usable to early select genotypes for an increased nutrient uptake efficiency. The main objective of this study was to determine the effects of these associations on plant total biomass and grain yield in durum wheat (cv. Anco Marzio). Secondly, we aimed to analyze the expression pattern of key genes involved in nutrient uptake. This experiment was carried out in a typical Mediterranean area (inner Sicily). Four types of biotic association in presence/absence of easily mineralizable organic nitrogen were considered: 1) not inoculated soil (control); 2) inoculated with a commercial mix of 8 AM fungal species; 3) inoculated with a commercial mix of 13 PGPR (Bacillus spp.); 4) inoculated of both AMF and PGPR mixes. Nitrogen content in aboveground biomass was determined at stem elongation stage. Quantitative RT-PCR assays were designed for nitrogen and phosphate transporter genes basing on sequence homologies with Triticum aestivum. Data showed an increase of total biomass when both PGPR and AM fungi were inoculated. In addition, PGPR inoculum determined a biomass increase when the organic fertilizer was supplied. These results can be explained by a synergistic effects of bacteria mineralization and AM nutrient uptake activities. Results of the ongoing gene expression analysis will be presented.