Optimizing Growth and Tolerance of Date Palm (Phoenix dactylifera L.) to Drought, Salinity, and Vascular Fusarium-Induced Wilt (Fusarium oxysporum) by Application of Arbuscular Mycorrhizal Fungi (AMF)

Abstract

Date palm (Phoenix dactylifera L.) is an important agricultural and commercial crop in the countries of North Africa and Near East. Date palm tree could be used for generations to come due to its remarkable nutritional, health, and economic value in addition to its aesthetic and environmental benefits. During the last decade, date palm plantations were subjected to degradation due to an extensive exploitation and to drastic environmental conditions. The major problems of drought and salinity have become more intense over time, and their negative impacts on palm crop are marked by decreasing the production of Phoenix dactylifera. Furthermore, fusarium wilts (bayoud) are economically important soilborne diseases that result in significant crop losses and damage to natural ecosystems. Bayoud is a vascular wilt caused by Fusarium oxysporum f. sp. albedinis (Foa) and represents the most serious fungal disease threatening date palm plantations. This vascular disease combined with the problems of drought and salinity causes huge losses in palm groves destroying more than 12 million trees and reducing the total areas from 150,000 to 44,000 ha. Plant–microbe interactions can be either beneficial or detrimental, and a fast and accurate assessment of the surrounding organisms is essential for the plant’s survival. Arbuscular mycorrhizal fungi (AMF) are a major component of soil fertility, and its use can improve crop resistance to biotic and abiotic stresses. This study highlights the importance of AMF in increasing tolerance of date palm to the combination of Fusarium oxysporum f. sp. albedinis and to water-deficit or salt stresses. Here, we investigated the consequences of date palm inoculation with four AMF spores: Glomus monosporus, Glomus clarum, Glomus deserticola, and Aoufous consortium (indigenous AMF) on morphological and physiological levels under F. oxysporum infection and drought or salinity stresses. Our results, after 14 months of growth, revealed that mycorrhizal infection rates were higher and slightly affected by water deficit. Aoufous consortium, G. monosporus, or G. clarum increased the biomass production of date palm despite the pathogen inoculation, independently of the water regime. AMF allowed maintaining high-level leaf water parameters in plants F. oxysporum inoculated or not under drought conditions. The mortality rate among the date palm trees infected by F. oxysporum was lower in mycorrhizal plants than non-mycorrhizal one. After 5 months of salt stress application (240 mM), AMF showed a positive effect on date palm tolerance compared to control (0 mM). Under salt stress, the aerial dry weight was increased more than twice in mycorrhizal date palm seedlings than in the control. Similarly, the water parameters including stomatal conductance, water content, and water potential were enhanced by AMF in the presence of salt stress. Our data suggest that AMF decrease the deleterious effect of F. oxysporum on date palm; nevertheless, the bioprotection against the plant pathogen was AMF species-dependent. The indigenous AM fungal community “Aoufous” resulted in a better crop resistance under harsh biotic and abiotic conditions.