Microbial Processes Promising Technologies for Developing Countries (1979) / Chapter Skim
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3 Soil Microbes in Plant Health and Nutrition
3 Soil Microbes in Plant Health and Nutrition
Pages 47-58
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From page 47... ...
In some cases, the invasion of roots by microorganisms is desirable. This is true for the root-nodule bacteria of the genus Rhizobium that fix nitrogen, as well as for mycorrhizal fungi, which assist roots in accumulating phosphate and other essential minerals.
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From page 48... ...
144. The sum of the various interrelationships of rhizosphere microorganisms and roots can benefit plant growth by influencing the availability of essential nutrients, by producing plant growth regulators, and by suppressing root pathogens.
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From page 49... ...
A recent report indicates that oxidation of hydrogen sulfide by a bacterium in the genus Beggiato a detoxified flooded rice soils. Beggiato a species may be significant in coastal marshes and estuaries as well as in rice paddies, and their capacity to influence plant growth favorably deserves further study.
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From page 50... ...
Many may also produce unidentified growth factors. Rhizosphere microorganisms are variously credited with promoting increased rates of seed germination, root elongation, root-hair development, nutrient uptake, and plant growth.
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From page 51... ...
These infected roots are called mycorrhizae. Although the mycorrhizal fungi probably increase uptake of all the essential elements, they are usually most important in improving phosphorus nutrition.
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From page 52... ...
In such soils inoculation may enable the use of inexpensive rock phosphate fertilizer instead of the more expensive super and triple phosphates. The major obstacle to greater use of VA fungi is the difficulty in obtaining inoculum.
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From page 53... ...
Ectomycorrhizae benefit trees by: increasing nutrient and water absorption from soil; increasing the tolerance of the tree to drought and extremes of soil conditions (acid levels, toxins, etc.~; increasing the length of the feeder root system; and protecting the fine feeder roots from certain harmful soil fungi. Ectomycorrhizal fungi cannot grow and reproduce unless they are in association with the roots of a tree host.
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From page 54... ...
By far the most biologically sound method of correcting an ectomycorrhizal deficiency is by the use of pure cultures of selected species of ectomycorrhizal fungi. In recent years, techniques have been devised to inoculate soil with pure vegetative and spore cultures of Pisolithus tir~ctorius in the United States and to introduce spore cultures of Rhizopogon luteolus onto pine seed and into soil in Australia.
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From page 55... ...
The production of vegetative cultures of ectomycorrhizal fungi requires aseptic culture technique. This means that the substrate on which the fungi are grown must be sterilized, usually by autoclaving, and maintained free of other microbial contamination for at least several weeks, or until the fungus has produced sufficient growth to overcome contamination.
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From page 56... ...
Their success in colonizing or infecting plant roots depends upon their ability to compete with other rhizosphere microorganisms. The chemical and microbiological environment in this zone may be altered slightly, but significantly, to effect changes in the inoculum potential of pathogens, either by selections of plant genotypes that produce such changes or by careful regulation of nitrif~cation in soil.
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From page 57... ...
1973. Microbial populations and nitrogen in soil growing consecutive cereal crops infected with take-all.
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From page 58... ...
Marx, Director and Chief Plant Pathologist, Institute for Mycorrhizal Research and Development, Forestry Sciences Laboratory, U.S. Department of Agriculture, Carlton Street, Athens, Georgia 30602, U.S.A.
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