ORIGINAL PAPER Water deficit improved the capacity of arbuscular mycorrhizal fungi (AMF) for inducing the accumulation of antioxidant compounds in lettuce leaves Marouane Baslam & Nieves Goicoechea Received: 15 March 2011 /Accepted: 22 August 2011 /Published online: 6 September 2011 # Springer-Verlag 2011 Abstract Lettuce, a major food crop within the European Union and the most used for the so-called ‘Fourth Range’ of vegetables, can associate with arbuscular mycorrhizal fungi (AMF). Mycorrhizal symbiosis can stimulate the synthesis of secondary metabolites, which may increase plant tolerance to stresses and enhance the accumulation of antioxidant compounds potentially beneficial to human health. Our objectives were to assess (1) if the application of a commercial formulation of AMF benefited growth of lettuce under different types and degrees of water deficits; (2) if water restrictions affected the nutritional quality of lettuce; and (3) if AMF improved the quality of lettuce when plants grew under reduced irrigation. Two cultivars of lettuce consumed as salads, Batavia Rubia Munguía and Maravilla de Verano, were used in the study. Four different water regimes were applied to both non-mycorrhizal and mycorrhizal plants: optimal irrigation (field capacity [FC]), a water regime equivalent to 2/3 of FC, a water regime equivalent to 1/2 of FC and a cyclic drought (CD). Results showed that mycorrhizal symbiosis improved the accumu- lation of antioxidant compounds, mainly carotenoids and anthocyanins, and to a lesser extent chlorophylls and phenolics, in leaves of lettuce. These enhancements were higher under water deficit than under optimal irrigation. Moreover, shoot biomass in mycorrhizal lettuces subjected to 2/3 of FC were similar to those of non-mycorrhizal plants cultivated under well-watered conditions. In addi- tion, lettuces subjected to 2/3 FC had similar leaf RWC than their respective well-watered controls, regardless of mycor- rhizal inoculation. Therefore, results suggest that mycorrhi- zal symbiosis can improve quality of lettuce and may allow restrict irrigation without reducing production. Keywords Anthocyanins . Carotenoids . Drought . Lactuca sativa . Mycorrhizal symbiosis . Phenolic compounds Introduction Lettuce (Lactuca sativa L.) is a major food crop within the European Union. According to FAOSTAT (FAO Statistics Division) 2011, the production quantity of lettuce and chicory in Spain, France, Germany and Greece were 1,000,000, 430,000, 320,000 and 80,000 tons, respectively, in 2009. Lettuce is the most used food crop for the called ‘Fourth Range’ of vegetables. The term originally meant fresh, cleaned, possibly chopped and mixed vegetables ready to be seasoned and eaten (Borghi 2003). These vegetables are widely accepted by consumers because they are easy to prepare for eating. Batavia Rubia Munguía (L. sativa L. var. Capitata) and Maravilla de Verano (L. sativa L. var. Capitata) are two types of lettuce extensively cultivated in greenhouses, highly commercialized and very appreciated to be con- sumed in salads in Spain. Both cultivars are characterized for an excellent shelf life that allows maintenance of their crispness from the time they are harvested until the time they are consumed. Batavia Rubia Munguía has yellow- green leaves, with very ruffled borders and a consistent, crisp texture. It develops a round, dense head. Maravilla de Verano has leaves with green color and red pigmentation especially in the borders of the most ruffled leaves. It develops good size, firm head. M. Baslam : N. Goicoechea (*) Dpto. Biología Vegetal, Sección Biología Vegetal (Unidad Asociada al CSIC, EEAD, Zaragoza e ICVV, Logroño), Facultades de Ciencias y Farmacia, Universidad de Navarra, Irunlarrea 1, 31008 Pamplona, Spain e-mail: niegoi@unav.es Mycorrhiza (2012) 22:347–359 DOI 10.1007/s00572-011-0408-9