Report on the Agricultural Experiment Stations, 1952 Page: 51
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REDUCING LOSSES FROM PLANT DISEASES 51
of the soils studied when mannitol was the energy source. The low
amount of available molybdenum may account for this failure in
The Idaho station demonstrated that the N-fixing bacterium Azotobacter
chroococcurn? produced more colored pigment (melanin) when
certain amino acids were included in the growth medium. When 0.01
percent boron was added to the substrate in the presence of these amino
acids (tyrosine, 8f-alanine, and glycine), still more melanin was
produced. The amino acids cysteine and cystine were found to inhibit
melanin production. Copper was also inhibitory to production
of this pigment, as well as to growth of the organism. The basic
metabolic rate of the organism as measured by oxygen consumption
was reduced by boron concentrations above 0.01 percent, but was not
influenced by lesser amounts of boron.
Adsorption of Nutrients by Bacteria
In attempting to find out how bacteria obtain mineral nutrients
from the soil, scientists at the Kansas station have shown that there
is no correlation between the electrical charge of bacterial cells and
their capacity to adsorb positively charged nutrient ions (cations).
Studies with enzyme-treated cells of different bacteria indicate that
adsorption takes place at the cytoplasmic surface underneath the cell
wall, and that it is probably not governed, therefore, by the surface
electrical charge carried by each cell. A constant-rate, continuousgrowth
machine was developed that will greatly facilitate the study
of surface phenomena.
Streptomycin in the Soil
Studies at the New Jersey station have shown that much larger
quantities of streptomycin are required to inhibit bacterial activity
in the soil than in solution substrates, and that the antibiotic is produced
in soils only under exceptional conditions. Most organic materials
that supported production of streptomycin by the streptomycinproducing
organism in culture substrates failed to produce the antibiotic
in the soil. The streptomycin is absorbed by higher plants
from culture solutions, persists in plants for some time, and is recoverable
in the sap. The antibiotic is decomposed so readily by microorganisms
in the soil that there is much doubt whether soil applications
can ever be relied upon for control of plant pathogenic organisms.
REDUCING LOSSES FROM PLANT DISEASES
The experiment stations are continuing to make material contributions
toward the solution of some of the baffling problems of plant
diseases. The research is directed (1) toward specific and immediate
problems affecting crop production, and (2) toward general development
of basic knowledge about plant diseases that is necessary to
help cope with new disease situations.
Recent progress in the making of scientific instruments and equipment
have been a boon to the plant pathologists. Development of
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United States. Office of Experiment Stations. Report on the Agricultural Experiment Stations, 1952, book, January 1953; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc5990/m1/53/: accessed October 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.