During studies on the effect of vesicular-arbuscular (VA) mycorrhiza, caused by species of Endogene, on plant growth, we needed to estimate the amount of mycorrhizal infection in the root cortex. Such infections in gramineous roots stain fairly clearly with standard procedures such as simmering in o·I % trypan blue in lactophenol (Hayman, 1970), or cotton blue and Sudan IV in lactophenol (Nicolson, 1959), and in some dicotyledonous roots by boiling for 10 min in 0'0 I % acid fuchsin in saturated chloral hydrate (Gerdemann, 1955), or standing cold overnight in any of these stains. Infection in onion, our main test plant (Hayman & Mosse, 1970), is difficult to estimate using these methods because, although external hyphae and entry points are strongly stained, internal hyphae, arbuscules and vesicles are usually only well defined near the cut ends of the root segments. To improve stain penetration and clearing in whole mycorrhizal roots of onion and other host plants, and in roots infected by other fungi, we developed...two procedures, which give deeply stained fungal structures which show distinctly against the outlines of the cells in the cortex of intact roots.

Improved procedures for clearing roots and staining parasitic and vesicular-arbuscular mycorrhizal fungi for rapid assessment of infection.

Summary
Assessment of infection is an essential part of many studies involving VA mycorrhiza. A summary is given of the range of techniques that have been used. We calculated the standard error of four methods of assessment based on observations of stained root samples either randomly arranged in a petri dish or mounted on microscope slides. The methods are based on presence or absence of infection at root/grid intersect points, on a visual estimate of percentage cortex occupied by fungus or on estimates of length, or presence or absence of infection in root pieces mounted on slides. The number of replicate observations required for a given standard error % infection can be read from the curves provided. The advantages of the different methods of assessment are discussed and reasons given why they all probably overestimate the true values.

https://nph.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1469-8137.1980.tb04556.x

An evaluation of techniques for measuring vesicular arbuscular mycorrhizal infection in roots

Previously described methods to quantify the proportion of root length colonized by vesicular-arbuscular (VA) mycorrhizal fungi are reviewed. It is argued that these methods give observer-dependent measures of colonization which cannot be used to compare, quantitatively, roots examined by different researchers. A modified method is described here to estimate VA mycorrhizal colonization on an objective scale of measurement, involving inspection of intersections between the microscope eyepiece crosshair and roots at magnification × 200; it is referred to as the magnified intersections method. Whether the vertical eyepiece crosshair crosses one or more arbuscules is noted at each intersection. The estimate of colonization is the proportion of root length containing arbuscules, called the arbuscular colonization (AC). The magnified intersections method also determines the proportion of root length containing vesicles, the vesicular colonization (VC), and the proportion of root length containing hyphae, the hyphal colonization (HC). However, VC and HC should be interpreted with caution because vesicles and hyphae, unlike arbuscules, can be produced in roots by non-mycorrhizal fungi.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1990.tb00476.x

A new method which gives an objective measure of colonization of roots by vesicular—arbuscular mycorrhizal fungi

Agency for International Development.

Vesicular-arbuscular mycorrhizal fungi can affect the water balance of both amply watered and droughted host plants. This review summarizes these effects and possible causal mechanisms. Also discussed are host drought resistance and the influence of soil drying on the fungi.

Water relations, drought and vesicular-arbuscular mycorrhizal symbiosis

The enhanced growth of plants infected by vesicular–arbuscular (VA) mycorrhizal fungi results primarily from improved uptake of soil phosphate. Extra phosphate reaches the root through the fungal h...

The physiology of vesicular-arbuscular endomycorrhizal symbiosis

Endogone spores and wheat roots were recovered from soil by wet sieving. Spore numbers changed little from December to June, greatly increased in July, and began to decrease in September. Formalin applied in 1967 decreased the number of spores present in 1968, more in soil not previously given formalin than in soil given formalin in 1964 and 1965. Plots without nitrogen and other fertilizers consistently contained more spores than plots with fertilizers. Vesicular-arbuscular mycorrhizal infection was sparse in May and increased during the summer to a peak in September. It was most abundant in plots containing most Endogone spores. Four spore types occurred in one Rothamsted wheat field, but only one type was found in a nearby wheat field. The increases in spore numbers and mycorrhizal infection during the summer suggest that Endogone has little effect on wheat during the spring period of rapid root and shoot development before flowering.

Endogone spore numbers in soil and vesicular-arbuscular mycorrhiza in wheat as influenced by season ans soil treatment

Plant growth responses to vesicular‐arbuscular mycorrhiza VI Effect of light and temperature

Summary
Mycorrhizal infections formed by different endophytes were examined in 10 crop species grown separately and in pairs in sterilized and unsterile soils. No infection was observed in cabbage, kale, rape or swede (in the supposedly non-mycorrhizal family Cruciferae) and only traces were seen in sugar beet (supposedly non-mycorrhizal Chenopodiaceae) when these plants were grown alone. However, slight (< 5 %) infection (cortical mycelium and vesicles, but no arbuscules) developed in some when a mycorrhizal host plant was present and there were many clumps of endophyte mycelium on their root surfaces, usually attached to entry points which had often aborted. Glomus fasciculatus‘E3’ was a more infective endophyte than Gigaspora margarita. Infection was usually well developed in the host plants barley, lettuce, maize, potato and onion. It was depressed only in a few pairs but no more by the presence of a ‘non-host’ plant than by a host plant. The results suggest that the barriers to mycorrhizal infection in ‘non-hosts’ are intrinsic and more probably related to characteristics of the root cortex or epidermis than to any infection-inhibiting factors that might be released in root exudates.

D. S. Hayman

Papers

Improved procedures for clearing roots and staining parasitic and vesicular-arbuscular mycorrhizal fungi for rapid assessment of infection.

The physiology of vesicular-arbuscular endomycorrhizal symbiosis

Endogone spore numbers in soil and vesicular-arbuscular mycorrhiza in wheat as influenced by season ans soil treatment

Plant growth responses to vesicular‐arbuscular mycorrhiza VI Effect of light and temperature

Influence of plant interactions on vesicular-arbuscular mycorrhizal infections. i. host and non-host plants grown together