## 3 Results
### Morphometric and Biochemical Parameters in the Second Growing Cycle  
A separate analysis of variance revealed significant effects (\(p\leq 0.05\)) of genotype (G: G\({}_{\rm{IL}}\), G\({}_{\rm{BL}}\)), irrigation treatments (I: I\({}_{100}\), I\({}_{80}\), I\({}_{60}\)), and mycorrhizalaae (M: NM and MT) and their interactions for morphometric and biochemical parameters in the second growing cycle (Supplement Table S2). Mycorrhizal treatment had a significant impact on HW, PH, RW, RL, DW, MDA, and proline, respectively. Irrigation treatment as well as I \(\times\) G interaction affected all tested variables. The genotype effect was significant for most of the variables (except RL). On the other hand, M \(\times\) I interactions were noticed for HW, PH, RL, LN, RW, RD, MDA, and proline, while the significant effects for M \(\times\) G were found for HW, PD, RW, SD, MDA, and proline, respectively. Finally, the impact of M \(\times\) I \(\times\) G was visible for PH, LN, RW, RL, RD, SD, MDA, and proline, respectively.  
In the second growing cycle the reduction of growth (HW, PH, PD, LN, RW, RL, and RD), was noticed in non-mycorrhizal treatment for iceberg and butterhead lettuce with the increasing drought level (Figure 2a-h). Furthermore, MDA and proline content showed a tendency to rise under water deficit (I\({}_{80}\) and I\({}_{60}\)) compared to control (Figure 3a,b). A comparative analysis also confirmed a positive association (r = 0.74) between proline and MDA content in the non-mycorrhizal treated group (Tables 2 and 3).  
Under optimal water conditions (I\({}_{100}\)), the root length (RL) of the iceberg was higher in the mycorrhizal group compared to the non-mycorrhizal group while in the butterhead the positive effect was notable for the aboveground growth parameters (Figure 2e,h). The application of beneficial microorganisms under medium drought level (I\({}_{80}\)) increased HW (Figure 2a), RW (Figure 2e), and RL (Figure 2f) in butterhead (Figure 2d). At the same drought treatment (I\({}_{80}\)), mycorrhizal treated iceberg's plants were higher (PH) than untreated although showed root growth inhibition (RW, RL), and decreased plant lateral growth (PD) (Figure 2c). A comparative analysis for nonmycorrhizal treatment showed a negative connection (\(p<0.05\)) between irrigation treatment and LN, RW, and RL, respectively (Table 2). Interestingly, exposure to mycorrhizal treatment under the highest drought intensity (I\({}_{80}\)) increased RW, and RL in both lettuce varieties compared to I\({}_{60}\) suggesting the biostimulatory role of mycorrhizal treatment (Figure 2a,f). In the second growing season, the MD of G\({}_{\rm{IL}}\) ranged from 0.47% (I\({}_{80}\)) to 8.10% (I\({}_{60}\)), while the MD of G\({}_{\rm{BH}}\) ranged from 0.53% (I\({}_{80}\)) to 5.96% (I\({}_{60}\)).  
scarcity treatments (Figure 3a). MDA content in the non-mycorrhizal group (I\({}_{60}\)) was 126% (butterhead) and 660% (iceberg) higher compared to mycorrhizal treated group. Correlation analysis revealed a strong negative correlation (\(p<0.05\)) between proline content and most growth parameters (HW, PD, PH, RL, RD, SD, LN) in non-mycorrhizal and mycorrhizal treated groups in both growing cycles (Tables 2 and 3). Comparing the impact of mycorrhizal treatment between lettuce genotypes, the application of mycorrhizal mixture promoted iceberg's root growth (RL) and proline accumulation in both irrigation treatments (I\({}_{80}\) and I\({}_{60}\)) compared to butterhead. On the other hand, butterhead lettuce had a higher stem lateral growth (SD) underwater optimal conditions (I\({}_{100}\)) and larger root weight (RW) than iceberg under medium drought stress (I\({}_{80}\)) (Figure 2e,h). In general, mycorrhizal dependency of both lettuce genotypes increased as water stress levels increased. In both growing cycles, the highest MD (17.4% and 31.3%) was recorded for G\({}_{\rm{IL}}\) on severe drought treatment (MT-G\({}_{\rm{IL}}\)-I\({}_{60}\)).