Arbuscular Mycorrhizal Fungi Limit Incidence of Fusarium oxysporum f.sp. albedinis on Date Palm Seedlings by Increasing Nutrient Contents, Total Phenols and Peroxidase Activities

Date palm seedlings derived from Jihel (JHL), a susceptible cultivar to Bayoud disease (fusariosis caused by Fusarium oxysporum f.sp. albedinis, Foa), were subjected to root inoculation with an arbuscular mycorrhizal fungus (AMF) collected from south Morocco and multiplied on barley as host plant. Successfully colonized plants by mycorrhizal fungi (85 % of treated plants) produced typical intraradical structures (arbuscules, vesicles, hyphae). After ten months of colonization, mycorrhizal plants showed a significant increase in their growth expressed as shoot height, number of leaves per plant, shoot weight, root weight and the total biomass. Mycorrhizal and non-mycorrhizal (controls) date palm seedlings showed great differences in their leaf contents of phosphorus (P), potassium (K) and sodium (Na). When compared with controls, P increased more than two folds in mycorrhizal plants, while the values of K and Na doubled. When inoculated with Foa by injecting roots with a spore suspension, mycorrhizal (M + Foa) and nonmycorrhizal (C + Foa) date palm seedlings showed significant increases in their root total phenols and peroxidase activities during the first month after inoculation. The highest increases were found in mycorrhizal seedlings accompanied by limited plant death. Mycorrhization alone did not affect significantly total phenols and peroxidase activities during the first week of culture. Plant death decrease in plant lots subjected to root inoculation with the he AMF fungus. As revealed by mycorrhization of date palm seedlings, these results supported the hypothesis that induced resistance to Bayoud disease is mediated by high increases in phenolic compounds and peroxidase activities. These results highlight the importance of mycorrhizal fungi as biocontrol agents to combat Bayoud disease and improve date palm culture in infected palm groves.