Effectiveness of arbuscular mycorrhizal fungi in the protection of olive plants against oxidative stress induced by drought

Olive trees are often subjected to a long dry season with low water availability which induces oxidative stress. The present study was conducted to evaluate the effectiveness of native Rhizophagus manihotis (Rma) and non-native Funneliformis mosseae (Fmo) arbuscular mycorrhizal (AM) fungi (AMF) in enhancing olive protection against oxidative stress induced by water deficit. Olive plantlets, cv. Picholine marocaine, were inoculated (AM-plants) or not (NM-plants) with Rma or Fmo and subjected to well-watered (75% of field capacity) or water-stressed (25% of field capacity) conditions. After two months, obtained results showed that water stress significantly decreased growth and biomass production of NM-plants, but AMF alleviated the detrimental effects of water deficit on the growth of olive plants. Inoculation with Rma increased shoot height by 120%, root length by 56%, fresh weight by 170% (shoot) and 210% (root), and dry weight by 220% (shoot) and 220% (root) compared to NM-plants. AM colonization enhanced drought tolerance in terms of protection against oxidative stress. Mycorrhizal plants showed lower levels of hydrogen peroxide (H2O2), malondialdehyde (MDA) and electrolyte leakage (EL) than NM-plants. Rma colonization decreased two times H2O2, 2.6 times MDA and two times EL levels compared to NM-plants. This protective effect seems to be due to the enhanced activities of superoxide dismutase (534 U mg(-1) protein), catalase (298 U mg(-1) protein), guaiacol peroxidase (47 U mg(-1) protein), and ascorbate peroxidase (305 U mg(-1) protein) which were highest in Rma-plants. Moreover, Rma-plants showed the lowest oxidative damage to lipid and highest soluble protein content. Thus, the native AMF Rma ought to be considered as a biological tool for enhancing olive tolerance to drought.