factors limiting symbiotic nitrogen fixation for crops in
developing countries. Though these expenditures are
still minimal compared with the importance of the
research they support, they are a beginning.
 Mycorrhizal-Root Interactions Mycorhizae are
fungi that colonize roots of practically all food crops.
Some 80 species live in and around root surfaces.
Mycorrhizae do not add nutrients or soil moisture to
soils, but they may greatly influence their use and
availability to plants and crops. Their presence may
increase by tenfold water and nutrient uptake of root
absorbing surfaces. Mycorrhizae also make phosphorus
and many micronutrients more available to plants on
phosphorus and nutrient-poor soils by converting
nutrients to more soluble forms and transporting them
to the roots of the plants. Mycorrhizae also favor
nitrogen-fixing bacteria. They can help plants with-
stand drought by transporting to plants water that is
beyond the normal reach of the roots. Mycorrhizae
may account for only 1 percent of the total weight of
plants, but they can give a 150 percent increase in
growth. One of the most exciting DISC research fron-
tiers is further study of the physiology and bio-
chemistry of mycorrhizae and other microorganisms in
the root zones of crop plants, and how their presence
relates to crop yields and the use of resources.
 Root-Colonizing Bacteria Bacteria of the genus
Pseudomonas constitute an additional frontier for
research in soil microbiology and crop productivity
(NAS, 1983). They suppress the growth of many plant
diseases caused by bacteria. Increased plant growth
and yields are closely associated with the capacity of
root-colonizing bacteria to produce iron-binding com-
pounds. It is suggested that the greatest possibility for
increasing crop yields and changes in agricultural prac-
tices for the future may involve the beneficial rhizo-
bacteria, which promote plant health by protecting
roots from the harmful microorganisms occurring in all
agricultural soils. The development of microbial pro-
ducts that are cost-efficient and adapted to fit the
technology of modern agriculture is a challenge for the
future.
 Nitrification and Denitrification Of importance
for the future is the more effective use of nitrogen ferti-
lizers applied to crops. Nitrogen losses now range from
50 to 75 percent. Two microbiologically powered
processes- nitrification and denitrification-cause
nitrogen to be lost from soils. Nitrogen stabilizers or
chemical nitrification and denitrification inhibitors
may reduce losses. Chemical inhibitors for both
nitrification and denitrification are now available.
Losses from denitrification can also be reduced by good
drainage and management, which require basic
research. Other approaches to better utilization in-
clude sulfur-coated urea, super granules of urea and


deep placement of these nitrogen fertilizers for certain
crops. The increased cost and limited effectiveness of
these materials and problems of handling and applica-
tion have thus far detracted from their widespread use.
Still another means of improving fertilizer uptake is
through trickle or drip irrigation systems. In some in-
stances, these may double the effectiveness of the
fertilizer.
 Somatic Cell Fusion and Tissue Culture- These
terms cover the techniques of growing isolated cells in
protoplast culture; anther, meristem and tissue
culture; haploid production; protoplast fusion; and
plasmid modification and transfer (National Academy
of Sciences, 1984). DISC research in genetics and cell
microbiology is producing significant advances in
techniques for isolating plant cells without walls and
providing cultures with appropriate growth regulants
for rapid regeneration into new plants. The majority of
these techniques have been developed during the past
12 years. So far the plants used have had little impor-
tance for farming or forestry. Some immediate oppor-
tunities in forestry could, however, be significant.
 Protoplast (vegetative cell) fusion produces somatic
hybrids that offer hope for tapping and creating
genetic materials not currently available because of
sterility barriers that prevent sexually crossing genera
and species. A somatic hybrid of the tomato and potato
is an example. As transformations and regeneration of
hybrids from protoplasts could greatly increase crop
production, DISC research in this area should be en-
couraged. The ability to reproduce genetic material
that can be readily introduced into established plant
breeding programs remains a major challenge. Pro-
toplast isolation and regeneration to whole plants from
vegetative fusion has thus far been confined mostly to
the Solanaceae and Cruciferae. No such hybrids have
yet been produced for any of the cereal grains, legumes
or other basic food crops.
 The most exciting developments thus far in genetic
engineering have not been with plants. In fact, bio-
technology for plants and crops is far behind that in
human and veterinary physiology and medicine
(Budiansky, 1984). The recent insertion of the gene for
the rat growth hormone into fertilized mouse eggs pro-
duced six extralarge mice, some twice normal size.
Matings of large male mice with normal females
resulted in both large and normal offspring, indicating
permanent incorporation of the rat gene in the mouse
DNA (Palmiter, et al., 1982). Ultimately, agricultural
applications will increase meat and milk production in
food animals.
 Applications of genetic engineering for crops will
likely occur first as a result of microbiological produc-
tions and transformations, mostly from Escherichia