Contents lists available at ScienceDirect Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti An endophytic fungi-based biostimulant modulated lettuce yield, physiological and functional quality responses to both moderate and severe water limitation Sergio Saia a , Giuseppe Colla b , Giampaolo Raimondi c , Emilio Di Stasio c , Mariateresa Cardarelli d , Paolo Bonini e , Paola Vitaglione c , Stefania De Pascale c , Youssef Rouphael c, ⁎ a Council for Agricultural Research and Economics (CREA), Research Centre for Cereal and Industrial Crops (CREA-CI), Vercelli, Italy b Department of Agriculture and Forest Sciences, University of Tuscia, Viterbo, Italy c Department of Agricultural Sciences, University of Naples Federico II, Naples, Italy d Consiglio per la Ricerca in Agricoltura e l’Analisi dell’Economia Agraria (CREA), Centro di Ricerca Orticoltura e Florovivaismo (CREA-OF), Pontecagnano Faiano, Italy e NGAlab, Tarragona, Spain ARTICLE INFO Keywords: Drought Flavonoids Funneliformis mosseae Leaf gas exchange Nitrate Rhizoglomus irregular Trichoderma koningii ABSTRACT Modulation of the water availability for the plants can be a sustainable option to reduce agricultural water demand and stimulate the synthesis and accumulation of secondary metabolites. However, information on the reduction of water availability while maintaining yield and functional quality are scarce and fragmentary. This research aimed at elucidating the agronomical, physiological and functional quality (ascorbic acid, phenolic acids and flavonoids) responses triggered by a microbial-based biostimulant containing two strains of arbuscular mychorrizal fungi (AMF) and Trichoderma koningii of greenhouse grown lettuce (Lactuca sativa L.) under well watered (WW), moderate (MDI) or severe deficit irrigation (SDI) regimes. Reducing water availability from WW to MDI did not affect yield, phenolic acids and flavonoids concentration, but reduced both AMF and Trichoderma presence in the roots and soil, respectively, along with plant Mg and Zn concentration by 12.4% and 26.8%, respectively, and almost halved net photosynthetic rate and transpiration. Further reduction in water availability also reduced yields, along with ascorbic acid, total phenols and quercetin. The biostimulant application in- creased a wealth of traits, including P, Mg, Fe, Mn, and Zn by 20.8%–97.4% and various phenolic acids com- pared to the non-inoculated control. This effect occurred irrespective of the water availability. In addition, the microbial-based biostimulant increased plant yield, Ca and Cu, and isochlorogenic acid concentrations, but such effects were evident under WW and MDI, only. Luteolin glycoside, that is frequently associated to a plant re- action to water deficit but also to a microbial stimulation, did not vary at reducing water availability in non- inoculated control and progressively increased in the biostimulant inoculated plant. These results suggest that the biostimulant effect on lettuce nutritional and functional quality was mostly independent of the water availability, whereas its effect on fresh marketable and dry yields were evident in WW and MDI, only, through a modulation of the biosynthesis of secondary compounds rather than nutrient uptake. These results have a high practical implication when aiming to improve both plant yield and product quality while reducing water availability. 1. Introduction Water shortage in agriculture is increasing and along with other abiotic and biotic stresses for the plants is harming plant yield and product quality under various conditions for both open-field and pro- tected cultivation (Mancosu et al., 2015). These issues are posing con- cerns for various aspects of the plant growth, that include at the one time a reduction of the yield potential and the product quality, with marked harmful side effects on both the profitability of the establish- ment, food security and food health properties (Bisbis et al., 2018; Wang and Frei, 2011). Horticultural crops, including leafy vegetables, depends on irrigation and inappropriate water supply has been reported to disturb several morphological, biochemical and physiological pro- cesses leading to stunted growth and crop productivity reduction https://doi.org/10.1016/j.scienta.2019.108595 Received 21 March 2019; Received in revised form 20 May 2019; Accepted 19 June 2019 ⁎ Corresponding author. E-mail address: youssef.rouphael@unina.it (Y. Rouphael). Scientia Horticulturae 256 (2019) 108595 0304-4238/ © 2019 Elsevier B.V. All rights reserved. T