Mycorrhizal fungi infect more plants than do any
other fungi and are necessary for many plants to thrive,
but they have escaped widespread investigation until
recently for two reasons. First, the symbiotic association
is so well-balanced that the roots of host plants show no
damage even when densely infected. Second, the fungi
cannot as yet be cultivated in the absence of a living
root. Despite these difficulties, there has been important
new work that suggests that this symbiotic association
can be harnessed to achieve more economical use of
costly superphosphate fertilizer and to permit better
exploitation of cheaper, less soluble rock phosphate.
Mycorrhizal benefits are not limited to improved
phosphate uptake in host plants. In legumes,
Mycorrhizal inoculation has increased nitrogen fixation
beyond levels achieved by adding phosphate fertilizer
alone. Certain symbiotic associations also increase the
host plant's resistance to harmful root fungi.