Plant-Microbe Cross Talk in the Rhizosphere: Introductory Remarks

Hyphal Growth and Conidia Germination Are Induced by Phytohormones in the Root Colonizing and Plant Growth Promoting Fungus Metarhizium guizhouense

“…Although the relationship between Metarhizium and plants has been studied, little is known about the chemical communication between them. Plants release secondary metabolites of high and low molecular mass to the rhizosphere, modifying the microbiota around the roots [ 2 , 36 ]. Some of these molecules released by plants are phytohormones, of which some phytohormones are released to the rhizosphere to establish the mycorrhizal association [ 1 , 10 , 11 , 14 , 15 , 17 ].…”

“…Strigolactones, which have been studied as a key factor in mycorrhizal association with AM and increased branching of hyphae in EC fungi, are released into the rhizosphere mainly when there is a nutrient deficit and stimulate hyphal growth and branching, increasing physical contact with the root. Thus, AM and EC compensate for the deficiency of these nutrients in the plant [ 13 , 21 , 36 , 46 , 47 , 48 ]. Synthetic strigolactones with biological activity such as rac-GR24 and other strigolactones, as described in sorghum, have been used; sorgolactone, both with biological activity involved in spore germination, increased the growth and branching of hyphae in AM [ 21 , 36 , 47 , 49 ].…”

“…Thus, AM and EC compensate for the deficiency of these nutrients in the plant [ 13 , 21 , 36 , 46 , 47 , 48 ]. Synthetic strigolactones with biological activity such as rac-GR24 and other strigolactones, as described in sorghum, have been used; sorgolactone, both with biological activity involved in spore germination, increased the growth and branching of hyphae in AM [ 21 , 36 , 47 , 49 ]. As in the aforementioned studies, strigolactones (GR24 and SorL) not only has an effect on AM fungi, but also, as observed here, has a positive effect on M. guizhouense .…”

“…The role of different phytohormones on rhizosphere fungi in modifying them in favor of the plant and establishing the beneficial association for both has been previously determined [ 36 ]. This association has been widely studied in AM and EC fungi and other endophytic soil fungi, but scarcely studied in the case of Metarhizium , which is also an inhabitant and component in the rhizosphere.…”

“…For example, Awad and collaborators in 2006 and Arens and collaborators in 2013 [ 18 , 47 ] identified that sorghum plants release strigolactones to the soil in concentrations ranging from 10 to 100 pmol per gram of soil, depending on the type of sorghum used, to establish mycorrhizal association with fungi. Other plants, such as corn ( Zea mays ) [ 18 ], flaxseed ( Linum usitatissimum L.) [ 46 , 55 ], cucumber ( Cucumis sativus L.) [ 55 ], lettuce ( Lactuca sativa ) [ 56 ], alfalfa ( Medicago sativa ) [ 57 ], tobacco ( Nicotiana tabacum ) [ 58 ], beans ( Phaseolus vulgaris ), japonica rice ( Oryza japonica ) and tomato ( Solanum lycopersicum ) [ 36 ], among other plants of agricultural interest, also produce different types of strigolactones to establish mycorrhizal associations.…”