The arbuscular mycorrhizal symbiosis can overcome reductions in yield and nutritional quality in greenhouse-lettuces cultivated at inappropriate growing seasons

• Growth and quality were determined in lettuces grown in different seasons.
• Winter was the most appropriate season for cultivating lettuces.
• Mycorrhizae improved growth and nutritional quality of lettuces in any season.
• Application of mycorrhizae may allow cultivating lettuces at not optimal periods.

The association of Lactuca sativa L. with arbuscular mycorrhizal fungi (AMF) can benefit growth and induce the accumulation of mineral nutrients and antioxidants in leaves. Our objectives were (1) to assess to what extent growing season influence growth and nutritional quality of the green-leaf Batavia Rubia Munguía (BRM) and the red-leaf Maravilla de Verano (MV) lettuce cultivars; (2) to test if the growing season affected the effectiveness of AMF as enhancers of the nutritional quality of the aforementioned cultivars; and (3) to check if inoculation with AMF allows extending the season to cultivate these two lettuce cultivars, without a loss of plant growth or nutritional quality. Results showed that winter was the most favourable growing season for both types of lettuce but mycorrhizal plants cultivated in other seasons different from winter achieved higher or similar shoot biomass than their respective non-inoculated controls in winter. AMF induced the accumulation of Fe, proteins, carotenoids and anthocyanins in both cultivars of lettuce in winter and spring. In summer and autumn, both types of lettuce showed increased levels of anthocyanins when associated with AMF. Mycorrhizal BRM also had enhanced levels of K, sugars and ascorbate in winter and spring as well as increased amounts of Mg and Cu in winter and summer. Mycorrhizal MV had increased quantities of Cu, Zn and sugars in spring and Mn in autumn. After estimating intakes of mineral elements through the consumption of 150 g per day of fresh leaves from mycorrhizal lettuces we may affirm that there would not be toxicological risk according to the Recommended Daily Allowances (RDAs). The application of AMF could allow extending cultivation of lettuce to other periods not appropriate for producing non-mycorrhizal plants.