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

Abstract

SUMMARYPreviously 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 x 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.

Chromium immobilization by extra- and intraradical fungal structures of arbuscular mycorrhizal symbioses

“…Detailed methods are described in the Supplementary Information. The ALP and ACP activity was assessed using the magnified intercepts method described by McGonigle et al [32] and expressed as percentage of total intercepts (200 hyphal intersections were assessed).…”

Arbuscular mycorrhizal fungi associated with the Meliaceae on Hainan island, China

“…Thirty root fragments (approximately 1 cm long) were mounted on slides in a polyvinyl alcohol-lactic acid-glycerol solution (Koske and Tessier 1983) and examined at 100-400× magnification under an Olympus BX50 microscope with an automatic photomicrographic system for the presence of AM fungal structures. The percentage of root length colonized by AM fungal structures was determined using the magnified line-intersect method of McGonigle et al (1990). The hyphae, arbuscules, and vesicles were recorded when any of them were presented at an intersection.…”

Uptake of Zn by arbuscular mycorrhizal white clover from Zn-contaminated soil

“…Stained root segments were mounted on microscope slides under coverslips. A magni®ed intersection method (McGonigle et al, 1990) was used to determine the proportion of root length infected. Five stained root segments were aligned perpendicular to the long axis of each slide and observed at´200 magni®cation.…”

“…with arbuscules, vesicles or hyphae) per slide. Three slides were examined for each treatment, giving a total of 150 counts per sample as recommended by McGonigle et al (1990).…”