Mycorrhizal fungus Rhizophagus irregularis protects olive trees from Verticillium wilt and promotes growth

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Abstract Arbuscular mycorrhizal fungus (AMF) Rhizophagus irregularis and its interaction with Verticillium dahliae were investigated in the susceptible olive "Picholine Marocaine" cultivar under controlled conditions. Olive plants were first inoculated with R. irregularis for three months, and then infected with V. dahliae. The present study assessed the impact of this combined inoculation on root colonization, plant growth parameters, nutrient uptake, and disease tolerance. Results showed that R. irregularis significantly increased mycorrhizal colonization in terms of vesicles and arbuscules compared to non-mycorrhizal controls, even in the presence of V. dahliae. This enhanced colonization was associated with improved plant growth, including increased shoot and root length, number of leaves and branches, and total dry biomass. Furthermore, R. irregularis significantly reduced disease severity as measured by dwarfing and leaf alteration indices. Mycorrhizal inoculation also led to a substantial increase in nutrient uptake, particularly potassium, calcium, and available phosphorus, in both shoots and roots of olive plants. Interestingly, sodium uptake was higher in plants solely colonized by R. irregularis, suggesting potential influence on specific nutrient dynamics. In general, this study demonstrates that R. irregularis can effectively promote root colonization, enhance plant growth and nutrient uptake, and significantly improve disease tolerance against Verticillium wilt in susceptible olive cultivars.