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FLORIDA STATE HORTICULTURAL SOCIETY, 1959 110 VIRUS DISEASE RESISTANCE IN PEPPERS A. A. Cook Florida Agricultural Experiment Station Gainesville Bell pepper production in Florida has been affected considerably by virus diseases in re cent years (1, 15, 17). Seven different viruses are known to infect peppers under field con ditions, but only five have been isolated from plants grown in central Florida (1). These are the tobacco etch, potato Y, tobacco mosaic, cucumber mosaic, and aster ringspot viruses. In certain localities within the state par ticular viruses may cause more damage than others. In central Florida tobacco etch, to bacco mosaic, and potato Y viruses were most frequently encountered by Anderson and Corbett (1). Simons (15, 17) found the cu cumber mosaic and potato Y viruses most detrimental in south Florida. Occurrence of the latter disease has been correlated with potato production (14). Virus disease (s.) can be controlled partially by several means. All such measures necessar ily affect 1) the original source of the in fection and its subsequent introduction into the crop field and/or 2) the spread of the infec tion within the field. The success of any at tempt at disease control is directly propor tional to its effectiveness against either or both of these factors. Crop plants may introduce the disease into the field if transplants are used. Seedlings may be infected while still in the plant bed, but show no symptoms until after transplanting. Perennial weeds in fence rows or along ditch banks frequently are infected with one or more of the viruses that affect peppers. Insects, particularly aphids, that have fed on such plants immediately before entering the crop field are one of the most important means by which virus disease(s) are introduced Florida No. 912. Agricultural Experiment Station Journal Series, into pepper fields. Some virus infections may be traced to field laborers who handle the plants, especially those who use tobacco. All of the viruses that affect pepper in Florida can be spread to healthy plants by laborers who have previously handled infected plants. Dissemination by this method may be considerable, particularly in the case of to bacco mosaic. Aphids, however, probably are the single most important means of withinfield spread. These vectors are capable of efficient transmission of the other four viruses despite the fact that they do not remain in fectious for a long time after feeding on a diseased plant. Their capabilities as vectors result from an ability to populate rapidly and because adults can fly considerable distances while infectious. Introduction of virus infections into the field through transplants can be avoided by direct seeding. None of the viruses affecting pepper in Florida infect the seed. Diseased plants should be rogued. In addition labor ers should wash their hands with soap and water before field work to reduce withinfield spread by laborers. Virus sources can be eliminated by the use of herbicides on ditch banks and fence rows. Particular attention should be given to eradication of such plants as nightshade, wandering jew, and Physalis sp. No practical method, however, has been de vised to eliminate the damage effected by in sects as vectors of virus diseases. Simons (16) found that neither insecticides nor border plantings of crops, that were physical barriers to aphid movement and immune to pepper viruses, were completely effective control measures. While there has not yet been devised a practical means of pepper virus disease con trol through use of cultural practices, some success has been attained from the use of re sistant varieties. Resistance to tobacco mosaic virus first was reported and studied by Holmes (8, 9), who noted two distinct types of re- COOK: PEPPER VIRUS RESISTANCE sistance. The most desirable type of resistance was characterized by a hypersensitive (ex tremely susceptible) reaction. Plants with this type of resistance, typified by the variety Ta basco, exhibited local necrotic lesions on in oculated leaves which dropped soon after in oculation. There was no further (systemic) development of the disease. Plants with the other type of resistance, termed "imperfect localization," showed large yellowish lesions. While there was systemic development of the disease in plants with this type of resistance, they did not become mottled and produced salable fruit. This information made possible the eventual development of varieties resist ant ("imperfect localization" type) to this disease, one of which was Yolo Wonder (11). Greenleaf (6, 7) noted resistance to tobacco etch virus in two species of pepper and de termined the nature of inheritance. This re sistance was found to result from a slow rate of virus multiplication within the resistant plants. Mild symptoms eventually appeared on many plants, but there remained a distinct difference in reaction of susceptible and re sistant plants. Workers in Puerto Rico (10, 13) found resistance to potato Y virus in a hot pepper (Cuaresmeno). This resistance was incorpor ated into a variety named Puerto Rico Won der (5, 12). That particular strain of potato Y virus found in Puerto Rico is distinct from the strains of this virus found in Florida, how ever. In view of the facts considered in the pre ceding discussion, a program was initiated to find, study genetically, and incorporate into an acceptable horticultural variety of bell pep per, resistance to the major virus diseases of pepper in Florida. All available pepper stocks1 were screened for resistance to 1) tobacco mosaic, 2) tobacco etch, and 3) potato Y viruses by mechanically inoculating test plants using the carborundum-gauze pad technique. A selection designated Pll, originally collected in Florida, was found to have resistance to all three viruses (2). One of the two peppers studied by Greenleaf (herein referred to as P342) was found also to be resistant to these diseases. 1 Kindly supplied by Associated Seed Growers, Inc., W. A. Burpee Co., Ferry-Morse, Kilgore, and F. H. Woodruff and Sons seed companies, Southern Regional Plant Introduction Station, Experiment, Georgia and colleagues of the author. - Designated S. C. 46252 by Greenleaf. 111 The resistance to the three viruses was not, however, of equal degree nor inherited in the same manner. Furthermore, some var iation in reaction to different strains of the same virus was noted. Plants of these two pepper lines, when inoculated with three strains of tobacco mosaic virus, reacted in a hyper sensitive manner. The inoculated leaves ex hibited local necrotic lesions within five days after inoculation. Within ten days these leaves dropped and there was no further develop ment of the disease. This reaction is typical for plants with the single dominant factor L. Some strains of tobacco etch virus caused symptoms in Pll and P34 plants only when a graft inoculation technique was used. A single recessive gene, designated eta by Green leaf, was postulated for this reaction. Pll and P34 plants were immune to five strains of potato Y virus. No symptoms were induced irrespective of method of inoculation. A single recessive gene, t/a, was proposed for this reaction (3). The discovery of the multiple virus disease resistance of these two peppers was signifi cant for several reasons. It was the first re ported instance of combined resistance to three virus diseases in pepper, a factor that should enable plant breeders to develop var ieties with resistance to more than one virus disease in considerably less time. The L type of tobacco mosaic resistance, unquestionably more desirable than the V resistance of var ieties now in production, had not been found previously in the bell pepper species (Capsi cum annuum L.) (18). Immunity to potato Y virus in pepper had not been noted previousFrom further studies it was determined that the genetic factors, L, eta, and t/a derived from Pll were the same as the corresponding factors from P34 (4). Furthermore, it has been established that the factors eta and ya in both peppers are closely associated on the same chromosome with the resistances resulting therefrom usually being inherited as a single factor. The preceding information has been ob tained by inoculation of progenies resulting from crosses between Pll and P34 and four commercial varieties of bell pepper. In the course of these studies to obtain basic in formation about virus disease resistance, in dividual plant selections have been made in 112 FLORIDA STATE HORTICULTURAL SOCIETY, 1959 an attempt to develop commercially accept able lines of bell pepper with resistance to all three viruses. This controlled breeding pro gram has now progressed through five genera tions in a period of three years with final selections anticipated within another two years. In the intervening time, studies similar to those described above for tobacco mosaic, to bacco etch, and potato Y viruses are planned for cucumber mosaic virus. Other investiga tions will include a critical evaluation, now in progress of a single line found to have resist ance to tobacco mosaic and potato Y virus. A limited quantity of seed of this latter pepper may be available for field testing in the fall of 1959. This pepper may alleviate in part the virus disease problems of the pepper in dustry in Florida until such time as other var ieties are available. LITERATURE CITED 1. Anderson, C. W. and M. K. Corbett. 1957. Virus diseases of peppers in Central Florida; survey results 1955. Plant Dis. Reptr. 41: 2. 143-147. Cook, A. A. and C. W. Anderson. 1959. Multiple virus disease resistance in a strain of Capsicum annuum. Phytopath ology 49: 198-201. 3. Cook, A. A. and C. W. Anderson. 1959. Inheritance of resistance to potato virus Y derived from two strains of Capsicum annuum. Phytopathology 49: (In press). 4. Cook, A. A. 1959. Genetics of resistance to two virus diseases in Capsicum annuum. (Abstract). PhytopatKota^v 49*. (In press). 5. Dale, W. T. 1956. Virus diseases of solanaceous crops in Trinidad. Tropical Agr. (Trinidad) 33: 35-50. 6. Greenleaf, W. H. 1953. Effects of tobacco etch virus on peppers (Capsicum sp.) Phytopathology 43: 564-570. 7. Greenleaf, W. H. 1956. Inheritance of resistance to tobacco etch virus in Capiscum frutescens and in Capsicum annuum. Phytopathology 46: 371-375. 8. Holmes, F. O. 1934. Inheritance of ability to localize tobacco mosaic virus. Phytopathology 24: 984-1002. 9. Holmes, F. O. 1937. Inheritance of resistance to tobacco mosaic disease in the pepper. Phytopathology 27: 637-642. 10. Perez, J. E. and J. Adsuar. 1955. Antigenic relation ship between Puerto Rican pepper-mosaic virus and a strain of potato virus Y. Jour. Agr. Univ. Puerto Rico 39: 165-167. 11. Porter, D. R. and S. G. Younkin. 1952. Introducing the new mosaic-resistant Yolo Wonder Pepper. Seed World 12. Riollana, A., J. Adsuar, and A. Rodriquez. 1948. Breeding peppers resistant to a Puerto Rican type of mosaic. Proc. Amer. Soc. Hort. Sci. 51: 415-416. 13. Roque, A. and J. Adsuar. 1941. Studies on the mosaic of peppers (Capsicum frutescens) in Puerto Rico. Jour. Agr. Univ. Puerto Rico 25: 40-50. 14. Simons, J. N., R. A. Conover and J. M. Walter. 1956. Correlation of occurrence of potato virus Y with areas of potato production in Florida. Plant Dis. Reptr. 40: 531-533. 15. Simons, J. N. 1956. The pepper veinbanding mosaic virus in the Everglades area of south Florida. Phytopathology 46: 53-57. 16. Simons, physical barriers J. N. on 1957. field Effects spread of of insecticides pepper and veinbanding mosaic virus. Phytopathology 47: 139-145. 17. Simons, J. N. 1957. Three strains of cucumber mosaic virus affecting bell pepper in the Everglades area of south Florida. Phytopathology 47: 145-150. 18. Smith, P. G. and C. B. Heiser, Jr. 1951. Taxonomic and genetic studies on the cultivated peppers, Capsicum annuum L. and C. frutescens L. Amer. Jour. Bot. 38: 362-368. VAPAM AND VPM SOIL FUMIGANT MUST BE APPLIED PROPERLY TO BE EFFECTIVE Donald S. Burgis and A. J. Overman Asst. Horticulturist and Asst. Microbiologist Gulf Coast Experiment Station Bradenton A new carbamate soil fumigant (sodium methyl dithiocarbamate, available commercial ly as Vapam and VPM) has given such good results in experimental plots that it is now recommended for field use. Increases in yield and quality of vegetables grown in soils treat ed with the fumigant are superior to those cur rently obtained from soils treated with the nematocides used for the past decade. This new fumigant differs in that it acts as an herb icide and soil fungicide as well as nematocide. The new fumigant injected 5 to 6 inches be low the surface o£ a row to be field-seeded to tomatoes 10 to 14 days following treatment allows the seedlings to emerge in a weed-free band 8 to 10 inches wide. The volatile gas released by the fumigant kills weed seeds and perennial grasses as it filters upward and escapes from the soil. Depth of the injection is very important. If it is too deep the fumi gant may not return to the surface so that all control in the top layer of soil is lost. If in jection is too shallow escape of the fumigant vapor may be too rapid, resulting in an erratic control of weeds and generally poor treatment. A depth of 5 to 6 inches below the surface of the finished bed has been found to be most satisfactory. When the decision has been made to fum igate a field, the first step is to begin the prep aration of the land early enough to insure the rotting of all previous crop roots and other plant debris. Maximum benefit of fumigation is dependent on the diffusion through the soil of the gases produced by the chemical and the vapors' contact with the disease or ganisms. Therefore, all plant parts in the soil must be well rotted so that the toxic vapors can reach the disease organisms which are generally harbored in the plant tissues. It is