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n. pl. mycorrhi·zae (-zē) or mycorrhi·zas
The symbiotic association of the mycelium of a fungus with the roots of a plant, as is found in the majority of vascular plants.

my′cor·rhi′zal adj.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


(Greek myco- fungus, rhiza root) an association between a FUNGUS and the roots of a higher plant. In some cases the fungus breaks down PROTEINS or AMINO ACIDS that are soluble and can be absorbed by the higher plant. In most cases, only nitrogen and phosphorus compounds result from fungal activity. Carbohydrates synthesized by the higher plants are absorbed by the fungus, so the relationship is a form of SYMBIOSIS. Some plants which lack chlorophyll, such as the bird's nest orchid, rely on mycorrhizas for carbohydrates in addition to protein.

There are two types of mycorrhiza: ectomycorrhiza and endomycorrhiza. In an ectomycorrhiza the infecting fungus occurs on the surface of the root and possibly between the cells of the root cortex, but does not penetrate such cells. The root becomes covered by a sheath of fungal tissue and looks different from an uninfected root. It is thicker, has no root hairs or root cap and may be a different colour. Ectomycorrhizae are found mainly on trees, such as oak and pine. In an endomycorrhiza the fungus develops within the cells of the root cortex. Subsequently the root cells digest the fungus leaving only knots of fungal material in the cells. There is usually little difference in the morphology of the root and a sheath of fungal tissue is not normally formed.

Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005
References in periodicals archive ?
There were significant differences in the stability of the date palm, caused by different irrigation regimes, Phosphorous rate, with or without of mycorhiza application and interaction effects are noticed.
Mycorhiza Treatments Colonization Forage dry matter % Kg [ha.sup.-1] 1:0(B) 22.8 6227.60d 3:1(B:P) 24.8 6375.60b Cropping system 1:1(BP) 24.8 6617.60a 1:3(BP) 25.1 6289.60c 0:1(P) 24 5552.6 43.5a 6224.70a 5.12b 6200.50b Arbescular mycorrhiza x Cropping system NS NS Table 3: Soil characteristics measured after crop harvesting.
The variance analysis (table 1) shows that the effect of mycorhiza on Kernels number is notsignificant .but effect of drought stress on Kernels number is significant at 1% of probabability Interaction of drought stress and mycorhiza on Kernels number is notsignificant, too.
Earlier mycorhizas have been reported to be associated with invasion of Erechites glomerata on Californian San Miguel Island (Halvorson & Koske, 1987).