Growth and Physiological Responses of the Ivorian Plantain Cultivar Affoto to Water Deficit and Rhizophagus irregularis Inoculation under Greenhouse Conditions

Abstract

Arbuscular mycorrhizal fungi (AMF) can improve plant performance under drought, but responses depend on host genotype, fungal isolate, symbiosis duration, and stress intensity. We evaluated whether Rhizophagus irregularis DAOM 197198 mitigated short-term water deficit in the Ivorian plantain cultivar Affoto under greenhouse conditions. Plants were assigned to a 2 × 3 factorial combination of inoculation (non-mycorrhizal or R. irregularis) and water supply (100% or 50% substrate water-holding capacity [WHC] replenished daily, or water withheld) for 14 days after a 14-day establishment period. Growth, organ water content, electrolyte leakage, chlorophyll index, leaf temperature, functional leaves, root colonization, and substrate spore density were quantified. Positive continuous responses were analyzed using log-linear models and heteroscedasticity-robust Type III tests; bounded responses were analyzed using beta or quasibinomial models. Water supply strongly affected total dry biomass (F2,36 = 34.44, P < 0.001), whereas inoculation (P = 0.789) and the inoculation × water-supply interaction (P = 0.946) did not. Mean total dry biomass declined from 104.73 g at 100% WHC to 70.58 g at 50% WHC and 36.02 g when water was withheld. Mycorrhizal growth responses were 2.7%, -4.1%, and -0.4%, respectively, and all 95% bootstrap confidence intervals included zero. AMF mitigation ratios were 0.935 (95% CI 0.627-1.422) at 50% WHC and 0.970 (0.626-1.572) under water withholding. Microscopy confirmed hyphae, vesicles, and arbuscules in inoculated roots, and none in controls; arbuscular abundance across the root system ranged from 24.92% to 31.81%. Thus, fungal establishment occurred, but inoculation did not detectably alter drought-associated biomass loss. Water deficit also reduced tissue hydration, growth dimensions, SPAD, and functional leaf proportion while increasing electrolyte leakage and leaf temperature. For the tested cultivar-isolate combination, following a short establishment period and under severe combined soil-water and atmospheric stress, R. irregularis conferred no detectable mitigation of biomass.