Comparison of different inoculants of arbuscular mycorrhizal fungi on Crocus sativus L. cultivated in soilless conditions.

Saffron (Crocus sativus L.) is an autumn-flowering geophyte widely cultivated for the most precious spice, consisting of the dried red stigmas of the flower. The violet tepals are considered a valuable by-product having a high content of phenolic compounds and antioxidant capacity. The use of biostimulants may improve the yield of the plant and quality of the flower. In the present study, different arbuscular mycorrhizal (AM) fungal inoculants, i.e., a single species of Funneliformis mosseae (Myc+ Fm) and Rhizoglomus irregulare (Myc+ Ri) or a multi-species mixture of Funneliformis geosporum, Funneliformis caledonium, and Claroidoglomus claroideum (Myc+ Mix), were tested on saffron plants grown in soilless conditions to highlight their efficacy in improving saffron production and tepals quality. The experiment took place in the Botanic Garden of Turin (Italy). Saffron plants were grown outdoors in a containment chamber in pots containing sterilized quartz sand. The yield of flowers, stigmas, and corms and the biomass of leaves and roots were measured. Tepal extracts were analyzed with the Folin-Ciocalteu method and the FRAP, ABTS, and DPPH assays. Morphological analysis of saffron roots revealed low AMF colonization, which could be due to saffron-AMF compatibility and/or growing conditions, particularly low temperatures. Agronomic measurements showed significant differences regarding the dried weight of leaves per corm (+29.6% for Myc+ Mix compared to Myc-). The antioxidant capacity analyzed in tepal extracts resulted significantly increased with the FRAP method for the treatments Myc+ Fm (+11.2%) and Myc+ Ri (+10.9%). An opposite result was seen for both ABTS and DPPH assays. Further studies could provide more information on the real influence exerted by AMF on saffron metabolism with the aim of improving flower secondary metabolites.