350 YEARBOOK OF AGRICULTURE 1953 environmental conditions; the host- range characteristics; the methods by which a virus can be transmitted from diseased to healthy plants; and the ability of a virus to live in extracted Virus Diseases plant juice or in dried tissue under different temperatures, and other phys- ical and chemical treatments for given of Cereal lengths of time. The method of perpetuating a virus is determined by the characteristics Crops of the virus. If the virus can be trans- mitted only by tissue union or by insects, it is kept alive in the living H. H. McKinney plant or sometimes in the living insects. Many viruses that can be transmitted Most of the plant viruses impair or experimentally by manual methods of destroy chlorophyll, the all-important inoculation are kept alive for months food-synthesizing green pigment in or years in frozen juice or in dried crop plants. The plant struggles for tissues near freezing. its existence or dies if its chlorophyll has The wheat, barley, oat, and cucum- been impaired. ber viruses that can be transmitted by Some viruses stunt or otherwise de- manual methods of inoculation arc form or alter the growth of plants with- kept in clipped leaf tissue that is de- out seriously affecting the chlorophyll. hydrated over calcium chloride, and Sometimes it seems that the chlorophyll stored over anhydrone at temperatures even may be increased. Some plants just above freezing. At intervals the may carry a virus but show no signs of stored viruses are increased in growing disease. plants, and new dehydrated tissues are Some viruses tend to impair or de- prepared and stored. The virus of stroy the chlorophyll uniformly through brome mosaic and viruses of the the leaf. They cause chlorosis—a gen- Agropyron mosaic can be maintained in eral yellowing or bleaching. In others that way, but usually less work is the impairment or destruction occurs involved when they are carried in their in patches, spots, or streaks in the leaf; respective native host plants, and the there is a light-green or yellow or white new cultures are started by the division mosaic mottling, spotting, or streaking. of the plant stools or from the rhi- The chlorotic patterns in the leaves are zomes. The virus of barley stripe strikingly similar for many of the virus mosaic can be kept in infected seeds diseases of the grasses, even though for at least 8 years. the viruses are quite different. Among the cereal crops in the United SoiL-BORNE wheat mosaic viruses States the greatest losses from the virus occur in Illinois, Indiana, Iowa, diseases are caused by the mosaics of Kansas, Maryland, Missouri, Nebras- winter wheat. Several viruses attack ka, North Carolina, Oklahoma, South cereals. Some have been controlled Carolina, and Virginia. Infected fields through the use of resistant varieties, have been found in nearly one-half of but for a destructive group of viruses in the counties in Illinois. Indiana also the area between Oklahoma to South has many infected areas. In many Dakota no effective control is known. places, particularly in Illinois, the We identify the viruses of cereals viruses would curtail the production and other plants largely on the basis of wheat were it not for resistant of symptom reactions of the infected wheats. plants when grown under proper These viruses of wheat and its close VIRUS DISEASES OF CEREAL CROPS 351 relatives also infect barley and rye, Along with the field experiments, although they have shown relatively microscopic studies that Sophia Ecker- high resistance. Oats, corn, and plants son, R. W. Webb, and I conducted at outside of the grass family apparently the University of Wisconsin revealed arc not susceptible to them. Bromus the presence of abnorrhal inclusion commutatus, a wild grass, is susceptible. bodies in many of the cells of both The viruses are not carried in the seed rosetted and mosaic plants. These cell from the diseased plants. inclusions were so strikingly like those The virus of w^heat mosaic-rosette associated with some known virus (Marmor tritici var. iypicum), is the first diseases, and the mosaic symptoms virus that we knew could be carried were so evident in many of the varie- over in the soil from season to season. ties of wheat, that we strongly sus- The rosette phase of the disease pected the virus nature of rosette and attracted attention in 1919, near the mosaics. Granite City, 111., but its virus nature Inoculation methods commonly used was not recognized until 1925. Previ- to transmit mosaic viruses in plants ously it was suspected that insects like tobacco and cucumber failed to (particularly the hessian fly), cold transmit the disease to healthy wheat winter temperatures, and several seedlings. Neither rosette nor mosaic species of fungi were causing the developed when I grew winter wheat trouble. In igsoit was learned that the out of its natural growing season. So I causal agent is associated with soils got the idea that cool temperatures and that it can be inactivated in the favor infection and disease expression. soil by steaming and treatment with Tests by Dr. Webb demonstrated formaldehyde. that soil temperatures near 60° F. and Many varieties of wheat were found comparatively high soil moisture fa- to be immune to rosette. From 1920 to vored natural infection from the soil. 1923 I selected rosette-immune strains When I inoculated healthy wheat from the highly susceptible varieties seedlings with the juice from the dis- Harvest Queen and lUini Chief. Years eased plants and then cultured them later, when Illinois 2 wheat was found at cool temperatures, they developed to be highly susceptible to mosaic- the disease. rosette, O. T. Bonnett and his associ- Mosaic symptoms are transmitted ates at the University of Illinois select- most successfully by growing the ed lines that w^ere immune to rosette inoculated plants with ample sunlight, and highly resistant to mosaic and that a daily photoperiod of 8 hours, and a had several of the desirable character- temperature near 60^. istics of Illinois 2. Those lines contrib- I observed that some of the wheat uted to the development of Prairie and plants growing in the field developed Royal varieties. light-green mosaic mottling. Others The evidence that the causal agent developed severe yellow mottling. In of rosette was associated with the soil the inoculation tests with virus from actually delayed the discovery that mosaic spelt and wheat plants, I saw a virus caused the disease. In 1920 that some of the plants of Harvest workers generally considered that Queen wheat developed light-green viruses did not overseason in the soil. mosaic and rosette, while others de- Even today few viruses are known to veloped yellow mosaic—somewhat like be carried over in the soil. Fortunately the situation that I had observed in the the rosette symptoms occur in only a study of the mosaic viruses that infect few varieties, such as Harvest Queen, tobacco. Virus-selection techniques mini Chief, and Missouri Bluestem. soon enabled the isolation of two Most varieties, however, develop mo- viruses. One induced mild light-green saic mottling when they are grown in mosaic and rosette in Harvest Queen infested soils. wheat. The other induced severe YEARBOOK OF AGRICULTURE 1953 yellow mosaic in Harvest Queen, but Schott-Jena fritted glass filter having no rosette. an average pore size of 880 milli- I found that most varieties of wheat microns. The dilution end points for the developed only mosaic when they were rosette and the yellow mosaic viruses inoculated with the mosaic-rosette in distilled water are between i oo and virus. Some varieties developed light- 1,000 times. green mosaic. Others developed mild Mosaic may occur in an infested yellow mosaic. field every year for at least 12 years, Some of the severe yellow mosaic or it may fail to appear after the first viruses that have been isolated from year. Air-dried soil stored in the the soil-borne series differ somewhat in laboratory for 3 years remained infec- their ability to destroy chlorophyll and tious. Some lightly infested soils lost to stunt or otherwise deform the plant. their infecting power when stored None, however, has been observed to through one summer, however. cause the excessive stooling or bud In a cropping test that covered 5 proliferation caused by the mosaic- years on infested land, Benjamin rosette virus. To distinguish them from Koehler, of the Illinois Agricultural other viruses that cause yellow mosaic Experiment Station, found that con- in wheat, they are referred to as the tinuous cropping with a susceptible prairie wheat yellow mosaic viruses wheat greatly favored the occurrence {Marmor tritici var. fidvum). Attempts of mosaic and rosette. Cropping for 4 to isolate a virus that induces rosette years with an immune wheat, oats, without the mild mosaic mottling soybeans, and corn greatly reduced or have failed. controlled completely the rosette and These yellow mosaic viruses arc re- mosaic in the susceptible wheats grown garded, as strains of the mosaic-rosette on the land the fifth season. Four years virus, but further study is needed to of cropping with alfalfa also reduced determine whether they are direct the amount of disease, but less than mutants or more distant relatives. I other crops did. Under favorable con- have not seen the strong unilateral in- ditions, which are not completely terference, characteristic of the tobacco understood, Dr. Koehler found that a mosaic virus in combination with its lightly infectious soil gradually became yellow mosaic virus mutants, in the highly infectious after four successive soil-borne viruses isolated thus far croppings with susceptible wheats. from wheat. It is therefore harder to The effects of various chemicals and demonstrate mutation in the wheat heat on infested soil have been tested mosaic viruses than it is in the tobacco by Koehler and me and also by Folke mosaic virus. Johnson at Ohio State University. The soil-borne wheat mosaic viruses Infestation can be eliminated by the are relatively unstable in extracted use of heat, formaldehyde, chloro- plant juices and in tissues removed picrin, dichloropropene-dichloropro- from the plant and kept at ordinary pane (D-D), napthalene, calcium temperatures. The viruses arc inactive cyanide, carbon disulfide, methyl bro- when the leaves die on the plant. When mide, rotenone, napthalene, and ethyl fresh mosaic leaves arc dried in the alcohol. Ethylene dichloride was less laboratory, the virus becomes inactive effective than the other chemicals. within 2 or 3 weeks. Furthermore, the Ethyl chloride gave no control. Tolu- viruses soon die when fresh mosaic ene gave no control in air-dried in- leaves are allowed to decompose in fested soil that was saturated with the moist soil. The thermal death point of chemical for 4 days, followed by com- the yellow mosaic viruses tested thus plete evaporation of the chemical and far is 140° to 149° F., with i o minutes seeding within 5 days to a susceptible exposure when in the plant juice. wheat. Traces of yellow mosaic virus passed a VVe do not know the exact relation VIRUS DISEASES OF CEREAL CROPS 353 of these wheat viruses to the soil. Per- SOIL-BORNE VIRUSES of oat mosaic haps they live in some soil-inhabit- occur in Alabama, Georgia, South ing organism that carries the virus Carolina, and North Carolina. The and introduces it into the under- mosaics were observed first in the ground parts of the young seedling in experiment station plots at Auburn, autumn. Ala. When they are abundant, they Any such vector must be very small, reduce the yields of grain and forage because dried infested soil remains in- of susceptible oat varieties such as fectious after passage through a 250- Bond, Camellia, Victoria, and Le- mesh Tyler screen. Many organisms toria. Growing resistant and tolerant (especially nematodes) in the soil varieties—Anderson, Atlantic, Appier, might serve as a carrier of virus, but Arlington, Custis, Fulgrain, Fulwin, no mosaic has been induced in wheat Lee, Lcmont, Victorgrain, Winter by the species of nema which have Resistant—should prevent widespread been used in tests conducted in collab- losses from the mosaics. The mosaics oration with Jesse R. Christie, of the have been observed in fields only in Department of Agriculture, and M. B. winter-grown oats and in oat relatives. Linford, of the Illinois Agricultural The viruses can be transmitted by Experiment Station. manual methods of inoculation when the oat plants are grown at tempera- THE PLAINS M^HEAT MOSAIC viruses tures near 60^ to 65^ F. Two viruses were collected by L. E. Melchers from have been isolated. One, Marmor a few scattered wheat plants growing terrestre var. typicum^ causes apical in nurseries and fields near Man- mosaic, a light-green mosaic mottling hattan, Kans., in 1931 and by me in that tends to be prominent toward 1941. Tests with the soil in which the the tip portion of the leaves of Letoria mosaic plants were growing failed to oats. The other, M. terrestre var. ocu- indicate that the viruses are soil-borne. latum^ causes eyespot mosaic, which in The viruses transmit by manual inocu- Letoria oats causes light-green or yel- lation with some difficulty even at low, nearly elliptical spots, which have favorable temperatures of from 60^ to green centers. Some plants in certain 65^. They cannot be maintained in oat strains that are grown in infested plants growing at summer tempera- soil develop a typical rosette. A specific tures at Beltsville. virus for oat rosette has not been We isolated green mosaic and yellow isolated. The viruses of these mosaics mosaic strains of virus. The green are not carried in seed from diseased mosaic strain does not induce rosette plants. In the soil they have shown in mosaic-rosette-susceptible Harvest much the same characteristics as the Queen wheat. Unfortunately the vi- soil-borne wheat mosaic viruses. ruses were lost in the summer of 1942, when no cool-temperature culture WHEAT STREAK MOSAIC viruses were chambers were available. first collected at Salina, Kans., in Soil-borne viruses isolated recently 1932, but records of L. E. Melchers from collections made in Kansas and make it seem likely that similar mosaics Oklahoma are so similar to the plains may have been present in Kansas be- wheat mosaic viruses that it is sus- fore 1930. In 1922 G. L. Peltier found pected that the viruses collected in a wheat mosaic in Nebraska that had 1931 and 1941 may have been soil- characteristics of streak mosaic. borne. The negative results obtained The disease has been worst in west- with the earlier collections of soil may ern Kansas, but it has caused damage have been due to a low level of in- in Nebraska, Colorado, a«nd South festation, and the plains wheat mosaic Dakota. Some damage has been re- viruses may be strains of Marmor ported in Wyoming and western Iowa. tritici. The disease is known to occur in Okla- 354 YEARBOOK OF AGRICULTURE 1953 homa, the Salt River Valley in Arizona, corn, oats, barley, several species of California, and Canada. In Nebraska winter annual bromegrasses, sand and South Dakota spring wheats as lovegrass, Canada bluegrass, some of well as wantcr w^heats are affected. the crabgrasses, and other range and Streak nnosaics gradually increased pasture grasses. over the years. In 1949 they caused an In some oats, the virus favors red- estimated loss of 7 percent of the dening in association with the chlo- wheat crop in Kansas. That amounted rotic patterns. In Golden Giant sweet to a loss of 30 million dollars. The corn, streak mosaic viruses induce a loss in 1951 also was heavy. It is not rather typical mosaic mottling, rings, uncommon to find entire fields and dots, dashes, and short streaks, some sometimes entire communities in which of which are elUptic and have green streak mosaic has wiped out the w^heat centers. The symptoms generally re- crop. The destruction of the chloro- semble those induced in field corn by phyll in the leaves frequently is so the sugarcane mosaic virus. The long, great that the plants are yellow. yellow, or bleached stripes associated Growth is halted and the plants fail with so many other viruses in corn are to set seed. not characteristic of streak mosaic. The viruses do not overseason in The plants are never killed, and infec- the soil. They are easily transmitted tion has never been obtained in all by manual inoculation at summer inoculated sweet corn plants. Some temperatures characteristic of Wash- lines of sugarcane develop local lesions ington, D. G. Infection is erratic at when the leaves of the true seedlings high summer temperatures, such as are inoculated with streak mosaic those that prevail at Stillwater, Okla. virus. The virus does not become sys- They are not seed-borne. Maybe some temic, though. Sorghum and the per- insect carries them. ennial smooth brome, Bromus inermis, The strains of streak mosaic virus are highly resistant or immune. Sev- range from those that induce severe eral of the susceptible forage and wild yellow spotting, streaking, and mot- grass species may contain resistant tling {Marmor virgatum var. iypicum)^ varieties. Tests have failed to reveal to those that cause mild, light-green any plant outside of the grass family or weak-yellow streaking and mottling that is susceptible to the streak mo- (Af. virgatum var. viride). With the saic viruses. strains of virus studied thus far, chlo- Because methods for inducing nat- rophyll destruction or yellowing is ural infection have not been worked favored by cool temperatures with the out, the wheat variety test nurseries daily averages ranging from 60° to have to be inoculated by spraying. 70°. Wheat varieties differ in the de- Varieties of wheat show some differ- gree of yellowing caused by a given ences in the reaction to streak mosaic, strain of virus. Under certain condi- but none has shown a safe degree of tions streak mosaics can be confused resistance to the severe yellow strains with the soil-borne virus mosaics. of the virus. The thermal death point of these High resistance and immunity have viruses in plant juice is near 129.2°, been found in rye, several wheat- with an exposure of 10 minutes. The grasses (species oîAgropyron), and some survival time at room temperature in of the hybrids between wheat and the air-dried leaf tissue has not been Agropyron species. more than 40 days. The dilution end point in water is near 5,000 times. BARLEY STRIPE MOSAIC virus was The virus passed a Berkefeld ''W" identified with the barley false stripe filter, pore size 3 to 4 microns. disease in 1950, but the disease has Streak mosaic viruses occur in sev- been known since about 1910. It used eral wild grasses. They can infect to be thought to be of nonparasitic VIRUS DISEASES OF CEREAL CROPS 355 origin. False stripe was first noted in stunted and usually worthless. The spring barley growing at the Wiscon- long yellow or bleached stripes in the sin Agricultural Experiment Station at foliage are like those induced by the Madison. Pressed specimens of the dis- brome mosaic virus, the cucumber eased plants, prepared by A. G. John- mosaic viruses, and by some leaf- son on June 27, 1913, and still in hopper-transmitted viruses that infect existence, leave little doubt that the corn. With the small grains, cool tem- symptoms are the same as those in- peratures favor strong symptoms in duced by the virus. Perhaps it was the the infected plants. first virus disease on a grass species to The thermal death point of the virus be collected in the United States. in plant juice is near 154.4° F., with 10 The disease occurs throughout the minutes exposure. The survival time spring barley region in the United in air-dried tissue at room temperature States, and it occurs in Canada. It has not been more than 40 days. The has not been regarded as a menace to dilution end point in water is slightly the crop. Pot tests out of doors prove, beyond 10,000 times. Traces of the however, that it causes serious reduc- virus have passed the Berkefeld "N" tion in the yield of grain and forage in filter, but not the Berkefeld ''W several varieties of spring barley. filter. The brown stripes often induced by Outstanding is the ability of the virus the virus in some plant species and to enter some of the seeds of the varieties tend to distinguish it from diseased barley and wheat plants. other viruses associated with grasses. Very few viruses are seed-borne; this The most common symptoms associ- was the first to be discovered in a grass ated with the virus, however, are the species. Because infected barley seeds unmistakable mosaic types of chlorotic tend to be poorly filled, many probably mottling, spotting, and streaking. The go with the screenings during threshing chlorotic areas in the leaves frequently and thus tend to keep down the occur- are ashy gray to white because of the rence of the disease. Tests have failed complete or nearly complete destruc- to show the virus to overseason in the tion of the carotinoids, or yellow pig- soil. ments, as well as the chlorophyll. The virus is transmitted easily by WHEAT STRIATE MOSAIC was dis- manual methods of inoculation at covered in winter wheat in South summer temperatures at Beltsville. It Dakota in 1950 by John T. Slykhuis, infects wheat, sweet corn, field corn, who succeeded in transmitting the smooth crabgrass, and occasional seed- virus to healthy wheat plants and re- lings of smooth brome. It has induced producing the disease by means of the only local lesions in inoculated leaves leaf hopper Endria inimica. Attempts to of rice and tobacco. In Michigan Am- transmit the virus by manual methods ber wheat seedlings, the first one or of inoculation have failed. The disease two leaves that develop systemic signs occurs also in Kansas and Nebraska. usually become almost solid ivory color The extent of the losses caused by or white, denoting a marked, acute striate mosaic is not known. phase of the disease. The seedlings are In Minter and Rushmore varieties, not killed. The new leaves become the disease shows up in fine, light- much less chlorotic in the chronic green or yellow lines in a streaked phase. But when infection is through pattern. In the early stages, the lines the seed, only the chronic symptoms are in the tissues directly over the appear, beginning with the first leaf veins. In Minter, brown necrotic spots of the wheat seedlings. In Golden may develop later. In Rushmore and Giant sweet corn and U. S. 13 field other varieties, the streaks are followed corn, the virus seldom kills the seed- by premature yellowing and death of lings, but the plants become badly the leaves. The diseased plants fre- 356 YEARBOOK OF AGRICULTURE 1953 quently are so stunted they produce when the plants are infected in their little or no seed. In the advanced early growth. stages, striate mosaic is readily confused The wheat variety Kanred has with other yellow mosaics of wheat. shown some tolerance to yellow dwarf, The host range of the virus is not but inoculated plants were stunted. known. AGROPYRON OR QUACKGRASS MOSAIC BARLEY YELLOW DWARF, another viruses were collected at Arlington new virus disease of cereals, was wide- Farm, Va. The green mosaic virus spread and destructive in California in {Marmor agropyri var. typicum)^ was 1951. John W. Oswald and Byron R. collected in 1934, and the yellow Houston found the virus to be trans- mosaic virus {M, agropyri var. flavum), mitted by five widely distributed was collected in 1936 in the same area species of aphids, the corn aphid from which the green mosaic virus was {Rhopalosiphum maidis), the apple grain collected. Mosaic was found in 1950 aphid (R. prunifoliae), the English in quackgrass in South Dakota by grain aphid {Macrosiphum granarium), John Slykhuis and in Iowa by Vernon the grass aphid (M, dirhodum), and the E. Wilson. In 1951 mosaic quackgrass greenbug {Toxoptera graminum). At- was found on the Plant Industry Sta- tempts to transmit this virus by manual tion grounds at Beltsville. At Arling- methods of inoculation have failed. ton Farm, the green mosaic virus was Wheat and oats have been infected isolated once from wheat growing near experimentally. the patch of mosaic quackgrass. The chlorotic symptoms induced by The viruses collected at Arlington the virus are similar to those caused by Farm transmit to quackgrass and to nonparasitic factors—an excess of soil wheat by manual inoculation, but water, drought, a shortage of nitrogen, with some difficulty. Infection and and low-temperature injury to the symptoms are favored by tempera- chlorophyll system. The light-green tures ranging from 60*^ to 65°, but or yellow mottling, the broken streak- infection will take place at summer ing, and the spotting that characterize temperatures. At the higher tempera- the other virus diseases of the small tures, however, the green mosaic fre- grains are relatively temporary or quently becomes masked and the absent in yellow dwarf. Leaves of yellow mosaic becomes very mild. infected plants rapidly turn light green The viruses overseason in the rhi- and yellow, beginning at the tips. zomes. Tests with soil in which the The chlorotic foliage tends to redden mosaic plants w^re growing in the field in oats, as when some of the non- failed to indicate ovcrseasoning in the parasitic factors are operating. Diag- soil. nosis therefore is difHcult, except in All attempts to infect Agropyron repens fields where the nonparasitic factors with the soil-borne wheat mosaic and other diseases can be excluded viruses have failed. from consideration. The most certain diagnosis is through transmission tests CORN STUNT was found in 1945 in the with one or more of the aphid vectors. San Joaquin Valley, Calif., by N. W. Plants become infected at all stages. Frazier, and in the lower Rio Grande Young plants are frequently killed. Valley, Tex., by George E. Alstatt. Stunting gradually decreases with The studies of L. O. Kunkel showed advancing age of the plant. Only the that corn stunt virus is transmitted by flag leaf shows signs of yellowing or the leafhopper Dalbulus (Baldulus) reddening when infection takes place maidus. The virus infects many varie- in the late stages of development. As ties of field corn, sweet corn, and with other virus diseases, the yield of teosinte, a close relative of corn. At- grain shows the greatest reduction tempts to infect the small grains, other VIRUS DISEASES OF CEREAL CROPS 357 grasses, and nongrass species have been virus apparently docs not infect any of unsuccessful. The virus cannot be trans- the small grains. mitted from diseased to healthy plants Several strains of the virus can be by manual methods of inoculation, but differentiated on sugarcane. At least Karl Maramorosch, of the Rockefeller four species of aphids transmit the Institute for Medical Research, suc- virus. ceeded in transmitting the virus to In studies by Hugo Stoneberg, this leaf hoppers by manual means. The mosaic had no apparent effect on the disease was reported from the Mesa rate of growth or the total height of Central, Mexico, by J. S. Nieder- the corn plants, and tended to increase hauser and J. Cervantes in 1950. They suckering and the number of ears found another leafhopper, Dalbulus slightly. Yields were reduced less than (Baldulus) elimatus^ that transmits the 10 percent, and the quality of the corn virus. was reduced slightly by the disease. In the early stages of corn stunt, the chlorotic spotting, streaking, and band- THE SOUTHERN CELERY MOSAIC virus, ing in the leaves resemble the markings a strain of cucumber mosaic virus associated with some of the mosaics. {Marmor cucumeris), infects corn in As the disease progresses, the signs several parts of Florida. Natural infec- resemble those associated with the tion is by the melon aphid. Aphis corn streak disease. In the advanced gossypii. Infections have been induced stages the leaves may be completely in teosinte, field corn, sweet corn, yellow or bleached; the leaves and kafir, sorgo, milo, wheat, and rye by stalks also may show a tinge of red. means of the aphid in studies con- Chlorotic markings appear in the ducted by F. L. Wellman. sheaths and husks. The upper part of In my tests with this virus and re- the stem may become chlorotic. The lated cucumber mosaic viruses, I was tassels may be deformed. Infected unable to infect wheat from manual plants tend to have short internodes inoculations, although infection could and extra shoots that originate from thus be induced in Golden Giant the axillary buds and from the ear sweet corn. In it the yellow stripes in branches, so that the plant is stunted the leaves are like those induced in and bushy. Husks tend to have unusu- corn by the mosaic (stripe) virus ally long tips. The ears produce few occurring in Cuba, Trinidad, and kernels. The roots and the brace roots Hawaii; by the barley stripe mosaic sometimes branch profusely and are virus; and by the brome mosaic virus stunted. when the corn plants are inoculated The disease tends to be more exten- after the seedling stage to avoid early sive in late corn than in early corn, death. probably because the insect carriers The cucumber mosaic viruses fre- are more abundant late in the season. quently kill sweet corn seedlings and The virus is not carried in the seed young plants in greenhouse tests. from diseased plants. Diseased plants that survive early infection are worthless for crop pro- SUGARCANE MOSAIC is the first virus duction. disease of grasses to be identified as such. The virus, Marmor saccharic was THE BROME MOSAIC virus {Marmor introduced from the Tropics. Soon graminis) has been collected in nature after its discovery, E. W. Brandes only on smooth brome {Bromus inermis) found out that the virus is transmitted from three locations near Manhattan, by the corn aphid, and that the virus Kans., and Lincoln, Nebr. No insect infects corn, sorghum, pearlmillet, vector for it is known. The virus in- and many other grasses in the South- duces local or systemic signs in a wide ern States where cane is grown. The range of grass species, including wheat, 358 YEARBOOK OF AGRICULTURE 1953 barley, oats, rye, corn, sorghum, and the period of the test, the plants were many wild grasses. Local lesions de- often walked on to simulate conditions velop on the inoculated leaves of some in a pasture. At the end of the test, 12 breeding lines of sugarcane in the out of the original 23 healthy brome- young seedling stage. It is one of the grass plants and 6 out of the original 27 few viruses tïiat can infect certain healthy orchardgrass plants had become nongrass species, besides grass. Its infected. The disease reduced the for- range among the nongrass plants age yield about 90 percent in the seems to be more limited than Pierce's smooth brome and about 80 percent in disease virus of grape, southern celery the orchardgrass. mosaic virus, and certain other strains Of the viruses that have host ranges of the cucumber mosaic group, which chiefly among the grasses, the brome also infect a few grass species. mosaic virus has the highest thermal Brome mosaic virus induces local death point (172.4° to 174.2° F., for 10 lesions in the wiped leaves of Samsun minutes), the longest survival time in Turkish tobacco, Early White Spine air-dried tissue at room temperatures cucumber, Scotia beans, some varie- (more than 20 months), and the high- ties of sugar beet, garden beets, Swiss est dilution characteristic (100,000 to chard, and lambsquarters (Chenopo- 300,000 times in water). The virus dium album). In lambsquarters all inocu- passed a Schott-Jena fritted glass filter lated plants give local lesions, and having an average pore size of 780 some of the plants in a population millimicrons. develop systemic chlorotic spotting. In the small grains, the symptoms it THE VIRUS OF PIERCE'S DISEASE of induces can be confused with those of grape and of alfalfa dwarf {Morsus suf- the wheat yellow streak mosaic virus. fodiens), infects an exceedingly wide The virus kills young seedlings of range of plant types, including grasses Golden Giant sw^eet corn, although and a sedge. Eight species of grass are the seedlings gain resistance as they known to become infected in nature in grow. When older plants become in- California. One is wild oats. Fifteen fected, their growing points are usually species of grass have been tested experi- killed, and the foliage develops yellow mentally, and 12, including barley, stripes or streaks resembling those became infected with the virus. Other induced by the barley stripe mosaic small grains were not tested, virus, the cucumber mosaic viruses, An outstanding characteristic is the and several of the leafhopper-trans- inability of the virus to induce appar- mitted viruses that infect corn. ent signs of disease in most of the plants Brome mosaic virus spreads easily it infects. None of the infected grasses at summer temperatures by manual has expressed symptoms, yet these methods of inoculation. Accidental in- hosts carry large amounts of the virus, fections from this virus nmst be guard- and they are favored by the leafhop- ed against more than with any other pers that transmit the virus. The asso- grass virus we know. There has been ciation of the virus with the xylem tis- no evidence of transmission of this sue may account for the suppression of virus through the seeds from infected symptoms in most plant species. The plants. fact that symptoms occur in grape and To determine the spread of brome in certain legume species, however, mosaic in the field, close plantings in suggests the possiblity that symptoms small plats of alternated healthy and might be incited in other plants by mosaic smooth brome and orchard- providing suitable environmental con- grass plants were observed by C. L. ditions. Lefebvrc and me. We started the test in the spring of 1946 and continued it SEVERAL VIRUS DISEASES of cereals through the 1947 crop season. During have not been found in the United VIRUS DISEASES OF CEREAL CROPS 359 States. All of the known viruses infect- CORN WALLABY-EAR VIRUS {Galla ing cereal species outside of continental Zeae)^ occurs in Queensland, Aus- United States and Canada, except the tralia. It is transmitted by the leaf- soil-borne wheat mosaic viruses in hopper Cicadula bimaculata. In young Japan, are transmitted by insects be- corn plants the virus induces elon- longing to some one of the so-called gated swellings, or galls, on the hopper groups of the order Homoptera. secondary veins on the under side of None is transmitted by manual meth- the leaves. The leaves tend to roll in- ods of inoculation. ward, as under conditions of drought, and their green color is intensified. CORN STREAK VIRUS and wheat stunt The plants are dwarfed. When older virus {Fractilinea maidis), cause serious plants become infected, the reactions diseases in corn and wheat in parts of tend to be mild. Africa. The best control of corn streak obtains when there is a break in the RUSSIAN WINTER WHEAT mosaic virus succession of crops, as corn seems to {Fractilinea tritici) is limited to Russia, be the best carry-over reservoir of the as far as we know. It is transmitted by virus. Three species of leafhopper, the leafhopper Deltocephalus striatus. Cicadulina mbila^ C. ^^¿z^, and C, nicholsi^ The virus infects winter and spring transmit the virus. The first symptoms wheats, rye, barley, and oats. It in- in corn consist of small, almost cir- duces light-green or yellow mottling cular, colorless spots. As the disease and streaking in the leaves. Infected progresses, the new leaves develop plants may be dwarfed. Some varieties narrow broken streaks, which are yel- of winter wheat proliferate, causing low and sometimes translucent. The rosette. Infected young plants are "A-form" of the virus species causes sometimes killed. The virus is not the wheat stunt disease in South Af- soil-borne. rica. The disease is destructive in early sown spring varieties because PUPATION DISEASE VIRUS of oats {Frac- the warm conditions favor the leaf- tilinea avenae) is also known as zakook- hopper vector, C. mbila. Resistant and livanie and Siberian oat mosaic virus. immune wheats are known. The chlo- It apparently occurs only in Siberia. rotic spotting and streaking in the The virus is transmitted by the leaf- leaves suggests some of the yellow mo- hopper Delphacodes {D elf ax) siriatella. saics of wheat. The infected leaves It infects oats, wheat, rye, barley, rice, tend to be curled. The bunchy, stunted corn, and several wild grasses. The plants resemble plants that have the symptoms in oats resemble those wheat mosaic-rosette disease. described for wheat mosaic caused by the virus Fractilinea tritici. The virus of CORN MOSAIC of Hawaii and the rice stripe disease in Japan is also corn stripe disease of Cuba are caused transmitted by Delphacodes striatella, by the same virus, Fractilinea zeae. suggesting that the virus F. avenae may The virus has been reported also from be the causal agent of this rice disease. Trinidad, Tanganyika, and Mauritius. It may occur in Puerto Rico, It has RICE DWARF VIRUS {Fractilinea oryzae) been found in sorghum. Transmission occurs in Japan and the Philippines. of the virus is by means of the leaf- The disease is also called rice stunt. hopper Peregrinas maidis. In corn, the The virus infects rice, wheat, rye, oats, chlorotic markings on the foliage re- and several wild grasses. It does not semble those associated with corn infect barley, corn, or sorghum. In- streak, as well as those associated with fected rice plants are dwarfed. The some of the mosaic viruses that can be young leaves have light-green or transmitted by manual methods of yellow spots along the veins. With the inoculation. succession of new leaves, the markings 360 YEARBOOK OF AGRICULTURE 1953 consist of chlor otic spots and streaks. The virus is transmitted by at least two species of leafhoppcrs, Nephoiettix apicalis (hipunctatus) var. cincticeps and Deltocephalus dor salis. Experiments with N. apicalis have shown that the virus The Smuts of passes through part of the eggs to the next generation, for as many as seven generations. Wheat, Oats, H. H. McKiNNEY holds degrees from Michigan State College and the University Barley of Wisconsin. In igig he joined the staff of the division of cereal crops and diseases of the Bureau of Plant Industry^ Soils, and C. S. Holton, V. F. Tapke Agricultural Engineering, where he has devoted most of his lim.e in research on Many millions of dollars' worth of viruses and virus diseases. grain are destroyed every year by the smuts of wheat, oats, and barley. For further reading: For purposes of study and control, //. H. McKinney: Evidence of Virus Muta- we can consider the smuts as being tion in the Common Mosaic of Tobcicco, seedling-infecting or floral-infecting. Journal of Agricultural Research, volume 5/, The seedling-infecting species come pages g^i-gSi, 1^33; Mosaic Diseases of Wheat and Related Cereals, U. S. D. A. Circular ^42, in contact with the host plants as ig37; Mosaic of Bromus inermis, Knih H. follows: The microscopic spores from Fellows and C. 0. Johnston, Phytopaihology, smutted plants are carried by wind, volume j2, page 331, ig42; Genera of the Plant rain, insects, and other agencies to Viruses, Journal oj the Washington Academy oj Sciences, volume 34, pages I3g-i54, 1944; De- the heads of healthy plants (as in scriptions and Revision of Several Species of loose smut of oats). Or, smutted Viruses in the Genera Marmor, Fractilinea, heads are crushed in threshing and and Galla, Journal of the Washington Academy spores are distributed to the clean of Sciences, volume 34, pages 322-329, 1944; Soil Factors in Relation to Incidence and Symp- seed or blown to fields, where later tom Expression of Virus Diseases, Soil Science, they come in contact with the host volume 6r, pages g3-ioo, 1946; Mosaics of at seeding time (as in the stinking Winter Oats Induced by Soil-borne Viruses, smuts of wheat). As the seed germi- Phytopathology, volume 36, pages 359-3^9, 1946; Stability of Labile Viruses in Desiccated nates and the seedling grows through Tissue, Phytopathology, volume 37, pages 139- the soil to the surface of the ground, 142, 1947; Wheats Immune From Soil-borne the smut inoculum develops thin Mosaic Viruses in the Field, Susceptible threads, which penetrate the seedling When Inoculated Manually, Phytopathology, volume 38, pages 1003-1013, 1948; Tests of and initiate infection. The fungus Varieties of Wheat, Barley, Oats, and Corn then grows internally in the plant for Reaction to Wheat Streak-Mosaic Viruses, and eventually forms spores in the Plant Disease Reporter, volume 33, pages 359—369, young heads. That completes the 1949; Mosaics of Winter Oats "and Their Control in the Southeastern States, with T. R. cycle and sets the stage for a new crap Staîiton, J, L. Seal, T. H. Rogers, W. R. Padcn, of smut. G. K. Middleton, and U. R. Gore, U. S. D. A. Circular 809, 1949', ^ Seed-borne Virus Caus- STINKING SMUT, or bunt, apparently ing False-Stripe Symptoms in Barley, Plant Disease Reporter, volume 35, page 48, ig5i; A has been a plague of wheat since wheat Method for Inoculating Varietal Test Nur- was first cultivated. It was prominent series With the Wheat Streak-Mosaic Virus, among the diseases studied by the with H. Fellows, Plant Disease Reporter, volume earliest plant scientists. It has been 35> P^g^^ 264-266, 1951; Wild and Forage Grasses Found To Be Susceptible to the Wheat widely investigated, and certain con- Streak-Mosaic Virus, with H. Fellows, Plant trol measures have long been known. Disease Reporter, volwne 35, pages 441-442, igji. Nevertheless bunt is still an economic