## 1 Introduction  
Drought is one of the major abiotic stresses that cause significant reductions in crop yield and quality [1, 2] and is expected to be more severe since the occurrence of drought is increased due to alteration in the evapotranspiration (ET) as well as unfavorable rainfall distribution caused by global warming [3, 4]. Several study results have shown that the negative consequences of drought can be overcome by adaptation of different strategies to improve the climate resilience of agriculture, i.e., sowing time [5, 6, 7], tillage systems [8, 9], irrigation [10, 11, 12], selection of crop and varieties [13, 14] and use of beneficial soil bacteria and mycorrhizal fungi [15, 16]. The latter was reported in the literature as a complementary measure that can mitigate the effects of biotic and abiotic stresses in crop production [16]. The literature review shows that mycorrhizal fungi can improve nutrient uptake [17, 18, 19] and increase the tolerance of crops against various abiotic stresses, i.e., high-temperature stress [20, 21, 22], salinity [23, 24, 25], and drought stress. The ability of mycorrhizal fungi to mitigate the negative effects of drought has been explored in prior studies by [PERSON] et al. [26], [PERSON] et al. [27], [PERSON] et al. [28], [PERSON] et al. [29], and [PERSON] et al. [30]. An earlier observation was given by [PERSON] [31]. The author emphasizes that the major problem in investigating the role of fungus in plant water relations is to distinguish between indirect effects such as enhanced nutrition and growth (e.g., greater plant mass, reduced rootshoot ratio) and direct effects of fungal hyphae. Recent research showed that Mycorrhizal plants increase stomatal conductance [30; 32; 33; 34; 35], leaf area [30; 32; 36; 37], transpiration rate [30], leaf water potential [38; 39; 40], net photosynthetic rate [30; 37] and relative water content [37; 41]. The development and effectiveness of mycorrhiza are closely related to the activity of beneficial soil bacteria, whereby the role is manifested in triggering various plant growth factors, leading to better availability of nutrients in the soil and uptake by plants [42]. In drought conditions, as well as other abiotic stress caused by environmental factors, plants produce antioxidants as a protector against oxidative damage. A series of recent studies have indicated higher superoxide dismutase (SOD) [30; 37], peroxidase (POD) [30; 37; 43; 44], and catalase (CAT) [30; 37; 44] in drought-stressed mycorrhizal plants, regardless of plant species. Furthermore, excessive production of reactive oxygen species (ROS) in stressed conditions causes malondialdehydedehyde (MDA) accumulation, which leads to cell membrane damage and, ultimately, cell death [45]. As stated by [PERSON] and [PERSON] [46] MDA is one of the final products of polyunsaturated fatty acid peroxidation in the cells and for this reason, it is a widely used and reliable marker for determining the degree of injury to a stressed plant. Previous studies have shown decreased MDA content, regardless of plant species subjected to drought stress and mycorrhizae [45; 47; 48; 49]. Proline is an osmolyte that provides plants with an osmotic mechanism to maintain a favorable osmotic potential for water uptake, therefore, alleviating the injury of drought stress [49]. The impact of mycorrhizae on proline content subjected to drought has been explored in prior studies by [PERSON] et al. [43], [PERSON] et al. [50], [PERSON] et al. [51], [PERSON] et al. [30], [PERSON] et al. [37]. In general, proline content was decreased in drought-stressed mycorrhizal plants. Studies on the negative impact of drought stress on lettuce yield and quality are well documented, it is also well acknowledged that the lettuce's highest yield, leaf number, plant weight, height and diameter, root weight, length, and diameter were obtained on no stressed treatments, that is on treatment with the highest irrigation rate [52; 53; 54; 55; 56].