Response to Inoculation with Arbuscular Mycorrhizal Fungi of Two Tomato (<i>Solanum lycopersicum</i> L.) Varieties Subjected to Water Stress under Semi-Controlled Conditions

Abstract

In arid and semi-arid regions, the growth and development of cultivated plants, especially tomato (Solanum lycopersicum L.), are severely limited by water deficit. Thus, to cope with this constraint, the plant establishes symbiotic relationships with arbuscular mycorrhizal fungi (AMF) in the soil whose extension of the hyphae allows a better and deeper exploration; this notably improves the hydromineral nutrition of the plant. Therefore, the choice of fungal partner becomes crucial for the establishment of a crop in water-deficient soil. In this context, the contribution of AMF to the water stress tolerance of two varieties of tomato plants was assessed under semi-controlled conditions. Parameters, such as the mycorrhizal frequency, intensity of mycorrhization, relative mycorrhizal dependency, growth, and biochemical parameters (carbon, nitrogen, phosphorus, and proline contents) of plants subjected to three levels of water stress (T100, T70, and T30), were evaluated. The highest frequencies and intensities of mycorrhization and relative mycorrhizal dependencies were obtained with plants of the Xewel variety inoculated with Rhizophagus fasciculatus (F: 95.24%, 88.35%, and 13.64%; M: 40.52%, 37.52%, and 11.22%; D: 23.7%, 54.4%, and 78.82%) and in those of the Lady Nema variety inoculated with Claroideoglomus etunicatum (F: 95.12%, 87.01%, and 15.25%; M: 40.66%, 37.99%, and 11.42%; D: 19.27%, 57.01%, and 70.98%), respectively at water regimes of T100, T70 and T30. These same symbiotic couples recorded, at T30, the best survival rates (+ 40%) and the higher aerial (77% and 74%) and root dry weights (80% and 59%). Plants of the Xewel variety inoculated with R. fasciculatus recorded the highest contents of carbon (T70: 30.59% and T30: 21.55%) and phosphorus (T70: 0.18% and T30: 0.17%). Plants of the Lady Nema variety recorded the highest nitrogen contents with 3.51% and 3.20%, respectively at T70 and T30. Plants of the Lady Nema variety, inoculated with C. etunicatum, also recorded the highest proline contents (572.25, 739.44, and 1165 nmoles•g−1 of fresh material), followed by those of the Xewel variety inoculated with R. fasciculatus (580.36, 763.65, and 1112.11 nmoles•g−1 of fresh matter), respectively at T100, T70, and T30. For the Lady Nema variety, the best fungal partner is C. etunicatum, followed by R. fasciculatus and, finally, Funneliformis mosseae. However, for the plants of the Xewel variety, R. fasciculatus is the most efficient, followed by F. mosseae and C. etunicatum. This suggests that, in tomatoes, the efficiency of mycorrhizal symbiosis under water stress conditions is not only dependent on the host plant but on both associated symbiotic partners. Hence, it is a need for screening to identify the best symbiotic couples in a stressful environment.