Synergistic effects of arbuscular mycorrhizal fungi associated to plant growth-promoting rhizobacteria in suppression of soil-borne Fusarium wilt of date palm

Soil-borne Fusarium wilt represents one of the major problems in the cultivation of the date palm. Arbuscular mycorrhizal fungi (AMF) consortium and plant growth-promoting rhizobacteria (PGPR) consortium were tested to determine the efficacy in disease management of Fusarium wilt. When applied individually, PGPR or AMF consortium reduced disease incidence, disease severity, and mortality rate of date palm seedlings. The combination of these consortia showed the best control efficiency which reflects a significant synergistic effect. The decrease in disease progression was accompanied by a significant promotion of plant immunity through the activation of the phenylpropanoid pathway, which was concreted by enhancement of PAL activity and accumulation of polyphenols and lignin content in date palm roots. In vitro antagonistic tests against Fusarium. oxysporum f. sp. albedinis (Foa) revealed that the bacterial strains of the PGPR consortium inhibited Foa growth, particularly the strain Bacillus cereus strain 263AG5' (60.59%). The evaluation of the mycorrhizal status of date palm roots after 27 weeks following the inoculation with Foa showed that the addition of both consortia was accompanied by a 3-fold increase in the intensity of mycorrhization and the arbuscules and vesicles number and 1.5 times increase in the frequency of mycorrhization. Our results highlight the high synergistic effect between PGPR and AMF consortia in date palm protection against Foa that could be attributed to the association of their antagonistic effect with their strong capacity for stimulation of plant natural defenses which suggests that these PGPR/AMF could be an effective approach to pathogen suppression.