To determine the spread of brome mosaic in the field, close plantings in small plats of alternated healthy and mosaic smooth brome and orchard-grass plants were observed by C. L. Lefebvre and me. We started the test in the spring of 1946 and continued it through the 1947 crop season. During the period of the test, the plants were often walked on to simulate conditions in a pasture. At the end of the test, 12 out of the original 23 healthy bromegrass plants and 6 out of the original 27 healthy orchardgrass plants had become infected. The disease reduced the forage yield about90 percent in the smooth brome and about 80 percent in the orchardgrass.

Of the viruses that have host ranges chiefly among the grasses, the brome mosaic virus has the highest thermal death point (172.4 to 174.2 F., for 10 minutes), the longest survival time in air-dried tissue at room temperatures (more than 20 months), and the highest dilution characteristic (100,000 to 300,000 times in water). The virus passed a Schott-Jena fritted glass filter having an average pore size of 780 millimicrons.

THE VIRUS OF PIERCE'S DISEASE Of grape and of alfalfa dwarf (Morsus suffodiens), infects an exceedingly wide range of plant types, including grasses and a sedge. Eight species of grass are known to become infected in nature in California. One is wild oats. Fifteen species of grass have been tested experimentally, and 12, including barley, became infected with the virus. Other small grains were not tested An outstanding characteristic is the inability of the virus to induce apparent signs of disease in most of the plants it infects. None of the infected grasses has expressed symptoms, yet these hosts carry large amounts of the virus, and they are favored by the leafhoppers that transmit the virus. The association of the virus with the xylem tissue may account for the suppression of symptoms in most plant species. The fact that symptoms occur in grape and in certain legume species, however, suggests the possibility that symptoms might be incited in other plants by providing suitable environmental conditions.

SEVERAL VIRUS DISEASES of cereals have not been found in the United States. All of the known viruses infecting cereal species outside of continental United States and Canada, except the soil-borne wheat mosaic viruses in Japan, are transmitted by insects belonging to some one of the so-called hopper groups of the order Homoptera. None is transmitted by manual methods of inoculation.

CORN STREAK VIRUS and wheat stunt virus (Fractilinea maidis), cause serious diseases in corn and wheat in parts of Africa. The best control of corn streak obtains when there is a break in the succession of crops, as corn seems to be the best carry-over reservoir of the virus. Three species of leafhopper, Cicadulina mbila, C. zeae, and C. nicholsi, transmit the virus. The first symptoms in corn consist of small, almost circular, colorless spots. As the disease progresses, the new leaves develop narrow broken streaks, which are yellow and sometimes translucent. The "A-form" of the virus species causes the wheat stunt disease in South Africa. The disease is destructive in early sown spring varieties because the warm conditions favor the leafhopper vector, C. mbila. Resistant and immune wheats are known. The chlorotic spotting and streaking in the leaves suggests some of the yellow mosaics of wheat. The infected leaves tend to be curled. The bunchy, stunted plants resemble plants that have the wheat mosaic-rosette disease.

CORN MOSAIC of Hawaii and the corn stripe disease of Cuba are caused by the same virus, Fractilinea zeae. The virus has been reported also from Trinidad, Tanganyika, and Mauritius. It may occur in Puerto Rico. It has been found in sorghum. Transmission of the virus is by means of the leafhopper Peregrines maidis. In corn, the chlorotic markings on the foliage resemble those associated with corn streak, as well as those associated with some of the mosaic viruses that can be transmitted by manual methods of inoculation.

CORN WALLABY-EAR VIRUS (Galla zeae), occurs in Queensland, Australia. It is transmitted by the leafhopper Cicadula bimaculata. In young corn plants the virus induces elongated swellings, or galls, on the secondary veins on the under side of the leaves. The leaves tend to roll inward, as under conditions of drought, and their green color is intensified. The plants are dwarfed. When older plants become infected, the reactions tend to be mild.

RUSSIAN WINTER WHEAT mosaic virus (Fractilinea tritici) is limited to Russia, as far as we know. It is transmitted by the leafhopper Deltocephalus striates. The virus infects winter and spring wheats, rye, barley, and oats. It induces light-green or yellow mottling and streaking in the leaves. Infected plants may be dwarfed. Some varieties of winter wheat proliferate, causing rosette. Infected young plants are sometimes killed. The virus is not soil-borne.

PUPATION DISEASE VIRUS of oats (Fractilinea avenue) is also known as zakooklivanie and Siberian oat mosaic virus. It apparently occurs only in Siberia. The virus is transmitted by the leafhopper Delphacodes (Delfax) striatella. It infects oats, wheat, rye, barley, rice, corn, and several wild grasses. The symptoms in oats resemble those described for wheat mosaic caused by the virus Fractilinea tritici. The virus of rice stripe disease in Japan is also transmitted by Delphacodes striatella, suggesting that the virus F. avenue may be the causal agent of this rice disease.

RICE DWARF VIRUS (Fractilinea oryzae) occurs in Japan and the Philippines. The disease is also called rice stunt. The virus infects rice, wheat, rye, oats, and several wild grasses. It does not infect barley, corn, or sorghum. Infected rice plants are dwarfed. The young leaves have light-green or yellow spots along the veins. With the succession of new leaves, the markings consist of chlorotic spots and streaks. The virus is transmitted by at least two species of leafhoppers, Nephotettix apicalis (bipunctatus) var. cincticeps and Deltocephalus dorsalis. Experiments with N. apicalis have shown that the virus passes through part of the eggs to the next generation, for as many as seven generations.

H. H. McKINNEY holds degrees from Michigan State College and the University of Wisconsin. In 1919 he joined the staff of the division of cereal crops and diseases of the Bureau of Plant Industry, Soils, and Agricultural Engineering, where he has devoted most of his time in research on viruses and virus diseases.