Use of arbuscular mycorrhizal fungi and beneficial soil bacteria to improve yield and quality of saffron (Crocus sativus L.)

A lot of information exists on saffron (Crocus sativus L.) culture, a very expensive process due to the low number of flowers formed on each corm. However, little is known about the use of beneficial soil microorganisms as arbuscular mycorrhizal fungi (AMF) and plant growth promoting bacteria (PGPB) as biofertilizers for saffron. Arbuscular mycorrhizae are the most common symbiotic association between plants and soil fungi of the phylum Glomeromycota. AMF improve mineral nutrition, plant growth and influence the whole plant physiology altering the hormonal profile as well as the production of secondary metabolites and plant flowering. The aim of our work, therefore, was to assess if the use of AMF and PGPB, alone or in combination, can positively affect flower phenology and secondary metabolite quality and/or production in saffron. Experiments were carried out by growing plants, inoculated or not with the beneficial microorganisms, in the field for two years. Cytological and morphometric analysis on both plant and stigmas and the chemical characterization (HPLC-DAD-MS) of the main molecules of saffron stigmas were performed. The results of the first year showed a significant increase of the bulb diameter, to which corresponded a higher flower production in the second year of growth. In addition, the time of flowering was differently affected by the beneficial microorganisms. Typical components of saffron, among which the crocine congeners, could be recognised. The relative intensities of the chromatographic signals were shown to depend on PGPB and AMF. Inoculation with AMF, alone or in combination with the bacterial strain, was the most efficient biotic treatment.