Research on arbuscular mycorrhizae in Mexico: an historical synthesis and future prospects

Effects of Arbuscular Mycorrhizal Inoculation by Indigenous Fungal Complexes on the Morpho-Physiological Behavior of Argania spinosa Subjected to Water Deficit Stress

Our objective is to test selected mycorrhizal complexes to verify the contribution of mycorrhizal symbiosis as a biological tool promoting the development of the argan tree under hostile conditions. In addition, this study aims to assess the impact of soil drought caused by stopping watering of young argan plants inoculated with strains of fungal complexes indigenous to the species in comparison to non-inoculated plants. Under conditions of water deficit stress, the most marked reductions in fresh and dry biomass were recorded in non-mycorrhizal plants. The most negative values of leaf water potential Ψf and Ψb were also noted in non-mycorrhizal plants. On the other hand, plants inoculated with mycorrhizal Bouyzakarne inoculum were relatively less affected by watering discontinuation compared to those inoculated with mycorrhizal Argana inoculum. Water stress caused a reduction in potassium and phosphorus content in the leaves and roots of all plants. However, mycorrhizal plants exhibited the highest P and K values compared to non-mycorrhizal ones. Therefore, mycorrhization compensates for the deficit in absorption of inorganic nutrients during drought. Sodium gradually decreased in the leaves but increased in the roots, and this delocalization of Na+ ions under water deficit stress resulted in higher concentrations in the roots than in the leaves of all plants. However, the mycorrhizal plants exhibited relatively lower values of root Na+ compared to the non-mycorrhizal controls. The water deficit reduced the content of chlorophyll a and b in the leaves and the chlorophyll a/b ratio in stressed plants. The lowest chlorophyll values were recorded in non-mycorrhizal plants. The levels of proline and soluble sugars in the leaves and roots of argan plants increased in all plants, especially with the extension of the duration of stress. However, proline accumulation was higher in mycorrhizal plants, with superiority in plants inoculated with the Bouyzakarne complex in comparison with that of Argana. In contrast, the accumulation of soluble sugars was higher in non-mycorrhizal plants than in mycorrhizal plants. We concluded that with a correct choice of the symbiotic fungi complexes, AMF inoculation biotechnology can benefit argan cultivation, especially under stressful conditions in arid regions with structural drought, where native Arbuscular mycorrhizal fungi levels are low.

Septoglomus mexicanum, a new species of arbuscular mycorrhizal fungi from semiarid regions in Mexico

Septoglomus mexicanum is here described as a new species of arbuscular mycorrhizal fungi (AMF; Glomeromycota) based on morphological and phylogenetic analyses. It was isolated from rhizospheric soil of two endemic Mexican legumes: Prosopis laevigata and Mimosa luisana, which grow in semiarid regions of central Mexico. Septoglomus mexicanum is characterized by forming globose spores of (154.5-)202.8(-228.9) µm diam and a spore wall consisting of four layers (SWL1-SWL4): outer wall layer (SWL1) hyaline, evanescent, (1.7-)3.2(-4.3) µm thick; SWL2 laminate and smooth, orange to reddish orange, (3.1-)4.5(-6.1) µm thick; SWL3 laminate, smooth, reddish orange to reddish brown, (4.1-)5.1(-5.7) µm thick; and SWL4 hyaline, semiflexible, (0.93-)1.2(-1.4) µm thick. None of the spore wall layers stain with Melzer's reagent. The subtending hypha has a color from yellowish to golden and presents a septum on spore base. Septoglomus mexicanum can be distinguished from all other Septoglomus species by spore size and color, by spore wall structure (four layers), and by color change of the subtending hypha. Phylogenetic analysis based on the AMF extended DNA barcode covering a 1.5-kb fragment of the small subunit (SSU), internal transcribed spacer region (ITS1-5.8S-ITS2), and the large subunit (LSU) of rRNA genes places S. mexicanum in the genus Septoglomus, separated from other described Septoglomus species, especially S. turnauae, with whom it could be confused morphologically. All available sequences in public databases suggest that this new fungal species has not yet been previously detected. Thus, there are currently 149 Glomeromycota species registered in Mexico, representing 47.4% of the known species worldwide.

[Temporal diversity dynamics of the arbuscular mycorrhizal fungi of Larrea tridentata (Sesse & Mocino ex DC) Coville in a semi-arid ecosystem]

Arbuscular mycorrhizal fungi (AMF) of arid and semiarid ecosystems are important for the development of plants that grow under biotic stress in wild or in agro-ecosystems. There is little information on the temporal diversity of these organisms in perennial plants from arid ecosystems in northern Mexico. On this study, the mycorrhizal colonization and the temporal diversity of AMF in the rhizosphere of Larrea tridentata, perennial plant abundant in the Chihuahuan Desert region were explored. Samples of the rhizosphere and roots of fifteen plants in each of the three sampling dates during the 2015 year were obtained. A total of 17 species of HMA belonging to 12 genera and 7 families within the phylum Glomeromycota in all three sampling dates were found. Funneliformis geosporum was the dominant species belonging to the family Glomeraceae which possess the highest genera number on L. tridentata. The highest mycorrhization percentage was in February with 83.22, followed by September and May with 75.27 and 65.27%, respectively. A maximum of 16 AM fungal species were isolated and identified from L. tridentata rhizosphere in February, 15 species in May and 12 species in September. Statistical analysis showed significant differences between sampling dates in the spores number.