A developmental study of the early stages in vesicular–arbuscular mycorrhiza formation

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Abstract
A new experimental procedure was developed to produce samples of leek roots containing early stages in colonization by vesicular–arbuscular mycorrhizal (VAM) fungi. This procedure involved transplanting leek seedlings into a pot culture containing an established symbiosis. Abundant colonization of seedling roots occurred in 1 week. Samples harvested at 2-day intervals after exposure to the inoculum were used to determine the time course of colonization. Contact of the root by external hyphae occurred after approximately 1 day, followed by penetration of hyphae into the root at about 2 days, arbuscule formation within 3–4 days, and vesicle formation after 4–5 days. The average distance from growing root apices at which each of the above events first occurred and the growth rate of intercellular hyphae were also estimated. Stages in root colonization were then documented using the chlorazol black E staining procedure. This transplant procedure should allow the production of abundant material at early stages in VAM development for chemical and morphological investigations as well as provide an efficient inoculation procedure.