Report on the Agricultural Experiment Stations, 1953 Page: 95
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PLANT DISEASE INVESTIGATIONS 95
of aphids, Macrosiphumr granarium, M. dirhodum, Rhopalosiphum
maidis, R. prunifoliae, and Toxoptera gramninum. Tests have shown
that the yellow-dwarf virus attacked 55 grasses which may furnish a
constant supply of the virus for aphids to transmit to the small grains.
The disease is expected to bring serious problems in California during
years when climatic conditions delay planting of grain until March
and at the same time are favorable to aphid reproduction and the
growth of susceptible wild grasses.
What may turn out' to be a closely related virus was found by the
Minnesota station to cause the blue-dwarf and red leaf disease of oats.
The virus nature and aphid transmission of red leaf seems certain,
and that of the blue dwarf probable. Neither disease was studied in
the absence of the other. It was not possible to transmit these diseases
Wheat streak mosaic was first found in Kansas in 1932. Although
the disease recently damaged wheat crops in several States in the Great
Plains region, it had never been understood how the virus could spread
so rapidly from plant to plant and field to field. Research started at
the South Dakota station and concluded at the Lethbridge station in
Canada has revealed the answer to a perplexing problem. It has now
been shown that the wheat streak mosaic virus is transmitted by a
tiny mite in the genus Aceria. The vector is so small that cages made
of 112-mesh sheer nylon proved ineffective in excluding the mite and
protecting the pot-grown wheat plants from becoming infected. These
results were further confirmed by the Nebraska station. The disease
can be successfully controlled in Nebraska by planting wheat in the
late fall and by eliminating sources of infection such as volunteer
wheat and grass weeds. The Nebraska station studies also disclosed
that there are probably nine or more virus entities that may cause
various wheat mosaics. The virus complex in cereals appears to be
much more intricate than heretofore supposed.
Basic work on the nature and behavior of cereal rusts at the Minnesota
station helps the plant breeder to produce and maintain resistance
in varieties of small grains. The rust situation is continually changing
and new races threaten previously resistant grain varieties.
Race 15B is now the predominant wheat stem rust strain in the
United States, comprising over 58 percent of the 1,279 isolates made in
1952. It now occurs throughout the United States, except the Pacific
Coast States, and in the principal wheat-growing areas of Mexico.
Of special interest was the occurrence of races 11, 49, and 139 that
heavily attack, under a wide range of conditions, some varieties and
breeding lines that are resistant to 15B.
Surveys made in 1953 revealed that all the durum wheats are more
susceptible to race 15B of stem rust than the bread wheats. Because
the durums mature 3 to 5 days later than the bread wheats, they are
subjected to rust infection longer and are more severely injured.
Survey data show that the durum wheats suffered severe losses in
North Dakota, South Dakota, and Minnesota in 1953.
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United States. Office of Experiment Stations. Report on the Agricultural Experiment Stations, 1953, book, 1953; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc5989/m1/97/: accessed October 18, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.