P. Abelson


ried out in many developing countries, including Brazil, Colombia, Costa
Rica, Cuba, Mexico, China, India, and Thailand.


 RHIZOBIA AND MYCORRHYZAE

 Plant biologists have long been aware of the role of rhizobia in nitrogen
fixation and of beneficial effects of mycorrhyzae in capturing phosphate.
Recent work has led to more systematic and effective use of these microor-
ganisms. The results are particularly applicable to developing countries
that are chronically short of hard currencies to pay for fertilizers. Rhizobia
naturally present in a soil are not necessarily optimum for the legume that
has been planted. On a recent visit to Brazil, I was told of a problem
encountered when farmers attempted to grow soybeans in a region of the
Cerrado. Nitrogen fixation was poor. The problem was traced to an Acti-
nomyces that secreted an antibiotic injurious to the rhizobia. Through
selection, a variety of rhizobia was obtained that is resistant to the antibi-
otic, and yields of soybeans improved. Considerable research is being con-
ducted in other developing countries to discover improved varieties of rhi-
zobia. Examples are India and Kenya. In Kenya, the effort has proceeded
to the point where 10,000 farmers have been provided with rhizobium
inoculants.
 Mycorrhyzae associated with plants can have very important beneficial
roles. Benefits can include enhanced efficiency of uptake of phosphate,
drought tolerance, broader pH tolerance, and resistance to certain patho-
gens. These fungi attach to plant roots and send out hyphae that increase
by, for example, a factor of ten the volume of soil tapped by the plant.
Many woody plants have ectomycorrhyzal fungi as their symbionts. Tech-
niques are available to grow the mycelia of these fungi in culture, and they
are commercially available in the United States. Millions of pine seedlings
are already being treated. Benefits include enhanced performance of seed-
lings in the nursery and better survival and growth in the field.
 The symbionts of most food crops and some trees invade the roots, re-
sulting in combinations called vesicular-arbuscular mycorrhyzae (VAM).
Until just recently, inocula were not commercially available. However,
Native Plants, Inc.(NPI) of Salt Lake City, Utah, has announced that it
can provide inocula. The NPI product is in the form of spores. Recently I
visited the laboratory of a subsidiary of NPI called Bio-Planta located in
Campinas, Brazil. There I saw a demonstration of the efficacy of VAM in
promoting the growth of lemon tree seedlings. The controls were only
about half as tall as the treated specimens, and the controls did not look