Biomass and Nutritional Status of Melon Hybrids Induced by Arbuscular Mycorrhizal Fungi Application Under Varying Irrigation Stress

Water scarcity is a major challenge in northeastern Brazil, where efficient water management strategies are essential for sustainable agriculture. This study aimed to evaluate the performance of melon hybrids in terms of biomass production and nutritional status under varying irrigation levels and mycorrhizal fungi (AMF) inoculation. The experiment was conducted in a greenhouse at the State University of Bahia (Juazeiro, BA, Brazil) using a randomized block design with a 4 × 2 × 4 sub-subdivided plot scheme. The treatments included four irrigation levels (50%, 75%, 100%, and 125% of crop evapotranspiration—ETc), two melon hybrids (Juazeiro and Mandacaru), and four AMF inoculation treatments (non-inoculated with AMF, <i>Entrophospora etunicata</i>, <i>Acaulospora longula</i>, and their combination), with 10 replications. The results indicated that the inoculation with <i>A. longula</i> significantly improved biomass production and plant nutrition, particularly for the Juazeiro hybrid. The most significant improvements were observed in biomass production and nutritional status when this mycobiont was used, highlighting the potential of AMF inoculation as a strategy to enhance water use efficiency and plant tolerance under water-limited conditions. Root colonization in melon plants ranged from 6% to 60%, with an overall average of 36.2%, in Experiment I, and from 6% to 72%, with an average of 40%, in Experiment II. Melon biomass production responded differently to irrigation levels, with Experiment I showing polynomial decreases in biomass as water levels decreased, while Experiment II exhibited linear increases in biomass with higher irrigation, likely influenced by supplementary fertilization. When evaluated, the levels of macronutrients present in the aerial part of the plants did not show significant differences for the treatments concerning the levels of P, K, and Mg, except for Ca. These findings suggest that <i>A. longula</i> is a suitable mycobiont for optimizing melon plant performance in regions with limited water resources, like northeastern Brazil. The study also emphasizes the importance of selecting appropriate Mycorrhizal fungi to maximize symbiotic benefits in melon cultivation under deficit irrigation systems.