viral coat protein. Even so, corn, in groups that contain known serotypes and 50:951-953. comparative experiments, afforded more require antiserum with broad cross- 6. MOORHEAD, E. L. 1959. Serological studies of extractable virus particles (ie, eight times reactivity, a single source viruses infecting the cereal crops. II. The of WSMV antigenic characteristics of wheat more than previously reported where streak mosaic antiserum apparently can be used for virus as determined by the complement fixation wheat and acid-heat treatment were used) routine virus diagnosis. technique. Phytopathology 49:151-157. with the purification procedure adopted 7. PFANNENSTIEL, M. A., and C. L. NIBLETT. here. The chloroform procedure was also 1978. The nature of the resistance of agrotricums simpler to perform to wheat streak mosaic virus. Phytopathology and required fewer LITERATURE CITED 68:1204-1209. steps than the acid-heat method. 1. BRAKKE, M. K. 1971. Wheat streak mosaic 8. SHEPARD, J. F. 1972. Gel-diffusion methods ELISA tests have been used to detect virus. No. 48. Descriptions of Plant Viruses. for the serological detection of potato viruses X, Commonw. Mycol. Inst., and differentiate virus serotypes (10). In Kew, Surrey, England. S, and M. Mont. Agric. Exp. Stn. Bull. 662. 4 pp. 72 pp. our WSMV-ELISA tests with relatively 2. BRAKKE, M. K., and E. M. BALL. 1968. 9. SHEPARD, J. F., and T. A. SHALLA. 1970. An low titer antiserum, however, the ease of Purification and antigenicity of wheat streak antigenic analysis of potato virus X and of its detecting different virus isolates (even mosaic virus. Phytopathology 58:963-971. degraded protein. I. Evidence for and degree of 3. FINLEY, A. M. though WSMV type strain was a distinct 1957. Wheat streak mosaic, a antigenic disparity. Virology 42:825-834. disease of sweet corn in Idaho. Plant Dis. Rep. 10. UYEMOTO, J. K. biotype) as well as a number of wheat 1980. Detection of maize 41:589-591. chlorotic mottle virus serotypes by enzyme- isolates recently collected in the field (J. 4. HOW, S. C. 1963. Wheat streak mosaic virus on linked immunosorbent assay. Phytopathology K. Uyemoto, unpublished), suggests that corn in Nebraska. Phytopathology 53:279-280. 70:290-292. 5. McKINNEY, H. the isolates are closely related anti- H., M. K. BRAKKE, E. M. 11. UYEMOTO, J. K., and R. G. GROGAN. 1969. BALL, and R. STAPLES. 1966. Wheat streak Chemical characterization genically. Hence, in contrast to virus of tobacco necrosis mosaic virus in the Ohio Valley. Plant Dis. Rep. and satellite viruses. Virology 39:79-89.

Evaluation of Cultivars for Resistance to Clubroot ( brassicae) Race 6 for Midwestern United States

RANDALL C. ROWE, Associate Professor, Department of , Ohio Agricultural Research and Development Center, Wooster 44691, and Ohio State University, Columbus 43210

ABSTRACT Breeding efforts with all crucifers have ROWE, R. C. 1980. Evaluation of radish cultivars for resistance to clubroot (Plasmodiophora been frustrated by the development of brassicae) race 6 for midwestern United States. Plant Disease 64:462-464. physiological races of the pathogen (2,4,12,15-17). This report summarizes Sixty-eight radish cultivars and breeding lines were tested in the greenhouse for resistance to greenhouse and field screening tests of clubroot caused by Plasmodiophora brassicae, race 6. Although most of the American radish germ plasm for resistance to P. tested were moderately to highly susceptible, all of the Japanese and many of the Dutch cultivars brassicae, race 6. were completely resistant. Further field tests of 16 Dutch radishes indicated that the cultivars Novitas, Roem van Zwijndrecht, Flevo, Robijn, Saxafire, Scharo, and Verano were resistant and MATERIALS AND METHODS horticulturally suitable for commercial production in the midwestern United States. Radish bulbs infected with P. brassicae were collected from a commercial muck farm in north central Ohio. These were Clubroot, caused by Plasmodiophora organic "muck" soil in Ohio and other sent to Paul Williams, Department of brassicae Wor., is a disease of worldwide midwestern states (13). The disease Plant Pathology, University of Wisconsin- importance in crucifer production affects the base of the bulb and the Madison, for determination of (2,5,9,11,17). the The fungus infects root taproot (Fig. 1) and necessitates extensive virulence spectrum of this population hairs of susceptible hosts and causes grading after harvest to remove infected using the concepts and standard set of 15 developing roots to form large distorted radishes. In severe cases, entire plantings European clubroot differentials (ECD) swellings and knobs (5,9). Severely have been destroyed. developed by Buczacki et al (4). Infected infected plants are stunted and often wilt Chemical control of clubroot has been bulbs collected at the same location were due to reduced root function. The fungus only partially successful. Root dipping of kept frozen at -18 C for use as inoculum forms resting spores within infected tissue transplants in fungicides containing throughout this study. that are released into the soil when the pentachloronitrobenzene (PCNB) or Sixty-eight radish cultivars and tissue decays. Spores can remain viable in benzimidazole derivatives has provided breeding lines from the United States, soil for at least 7 yr (5,9), and heavily control in some cases (1,3,10,12,17) but Europe, and Japan were evaluated in the infested fields may have to be abandoned has been completely ineffective in muck greenhouse for clubroot resistance during for crucifer production. soils (6,8). A preliminary study we January and February 1979. Muck soil In recent years, clubroot has become a conducted confirmed that these com- was placed in 30 X 60 X 7 cm wooden limiting factor in the production of pounds were ineffective in controlling flats, and radish lines were seeded in radishes (Raphanus sativus L.) on radish clubroot when incorporated into single rows 30 cm long and 10 cm apart. muck soil (14). Two replicates of one row each were used Approved for publication as Journal Article No. 200- The main thrust of clubroot control for each line. Resting spores of P. 79 of the Ohio Agricultural Research and has been based on developing resistant brassicae were extracted from frozen Development Center, Wooster 44691. cultivars (9,11,17). Differences in radish bulbs by comminuting "clubbed" the susceptibility among radish cultivars roots with a small volume of 00191-2917/80/05046203/$03.00/0 were observed quite early (7), but only a sterile distilled water in a blender for I 01980 American Phytopathological Society few studies have been made since then (9). min, filtering through cheesecloth, and 462 Plant Disease/Vol. 64 No. 5 adjusting the final spore concentration to marketable yield, which is reported in most suited to commercial radish approximately 1.7 X 106/ ml. About 30 ml detail in a separate paper (13). production in the midwestern United of this suspension was poured uniformly From these data the following resistant States: Novitas, Roem van Zwijndrecht, over each row of seeds before covering Dutch cultivars (listed in approximate Flevo, Robijn, Saxafire, Scharo, and with soil. After I wk, seedlings were order of preference) appear to be those Verano (Table 1). thinned to 10 per row. Plants were grown in the greenhouse at 20-25 C under fluorescent lights with a 12-hr photoperiod Table 1. Response of 68 radish cultivars and breeding lines to Plasmodiophorabrassicae race 6 in greenhouse and hlx. Soil was kept at or near field evaluations at 100-200 b Susceptibility field capacity by frequent watering. Six Radish radishes were type' Greenhousec Fieldd weeks after seeding, mature Entry- -- i Origin uprooted and examined for clubroot Novitas' I Holland 0 0 symptoms and horticultural character- Roem van Zwijndrecht' I Holland 0 0 istics. Flevoe Holland 0 0 Robijn' Holland 0 0 Cultivars resistant in greenhouse tests Saxafire Holland 0 0 were further evaluated in field tests in Scharo Holland 0 0 August 1979 at two commercial muck Verano Holland 0 0 farms in northeast and north central Kokarde Holland 0 0 Korda Holland 0 0 Ohio. Identical plots were planted at each Middle East Giants Holland 0 0 location on naturally infested soil and a Americano Holland 0 0 third was seeded on uninfested soil at the Sarxkatra Holland 0 0 north central location. Seeds of each Qumkader Holland 0 0 Real Holland 0 0 variety were put into separate hopper Scarabelle Holland 0 1 boxes of a commercial radish drill, and Piggelmee Holland 0 single rows about 100 m long were Kader Holland 0 planted. Four weeks later, 100 mature Minitas Holland 0 Robino Holland 0 radishes were harvested by hand from Katra Holland 0 each row and evaluated for clubroot Rota Holland 0 development and horticultural character- Radar Holland 0 istics. RS 1004 Holland Risenbutter Holland RESULTS AND DISCUSSION Prinz Roten Holland 2 Bolide 2 Holland 3 The infection pattern of the population Saxerre France 0 of P. brassicae obtained from Ohio Crimson Giant United States radishes on the 15 European clubroot Novired United States 2 differential hosts was ECD 16/6/30 (4). Cavalrondo United States Crimson Knight United States This response indicates that this Champion United States 2 population varies only slightly from those Cherry Bell United States 2 normally found in the midwestern United NK3 United States 2 States in fields planted to Brassica NK8 United States 2 Red Boy United States 2 oleracea crops such as , , Scarlet Knight United States 3 3 , and brussel sprouts. This Red Prince United States 3 3 population, commonly referred to as race Scarlet Globe United States 3 6, gives an infection pattern of ECD Early Scarlet Globe United States 3 United States 3 16/2/30. The difference between these Scarlet Globe Short Top 6 Stoplite 6 United States 3 two designations is that approximately Comet 6 United States 3 half of the ECD No. 8 differential plants Cavalier 6 United States 3 (Brassica napus) were suscep- NK7 United States 3 NKIO United States 3 tible while the others were resistant, NK13 United States 3 indicating a buildup of virulence in the NK15 United States 3 population capable of infecting this Fuego United States 3 normally resistant differential. Far Red United States 3 Round Scarlet Giant 2 Japan 0 Greenhouse tests of radish cultivars Lange Scharlaken Rode 2 Holland 3 indicated that most of the American Long Scarlet Globe 2 United States 3 radishes were moderately to highly French Breakfast United States 3 susceptible to this population of P. 18 daagse Halflange 3 Holland 2 brassicae, whereas all of the Japanese and Rode Witpunt many of the European radishes were Halfrood/ Half wit 3 Holland 3 Ronde Rode Kleinwitpunt 3 Holland 3 resistant (Table 1). Sixteen resistant Sparkler 3 United States 3 European cultivars that were horticul- Ronde Witte 4 Holland 0 turally similar to the red bulb-type Ijskegel 5 Holland 2 2 radishes grown in the United States were Icicle Short top 5 United States Ookura 6 Japan 0 further evaluated in the field along with Shogoin 6 Japan 0 standard American cultivars. In these Wakayama 6 Japan 0 tests, serious clubroot developed only on Shikou Japan 0 Nezumi Japan 0 the infested plot at the north central farm Hooryo Japan 0 where 14 Dutch cultivars remained Shirokubi-Myashige-Maruziri Japan 0 completely resistant while the susceptible I = red bulb type, 2 = elongated red bulbs, 3 = red bulbs with white tips, 4 = white bulb type, 5 = white icicle type, standards, Scarlet Knight and Red 6 = large, elongated, white Japanese type. Prince, were 100 and 68% infected, b0 = resistant (no sign of infection), I = slightly susceptible (< 10% of bulbs with clubbed roots), 2 = moderately susceptible (10-30% of bulbs with clubbed roots), 3 = highly susceptible (> 30% of bulbs with clubbed roots). respectively. At the other two locations, 'Test consisted of two replicates of 10 plants each. all cultivars were evaluated for desirable dEvaluation consisted of 100 plants pulled at random from about a 100-m row. horticultural characteristics as well as eResistant and horticulturally suitable for commercial production in the midwestern United States.

Plant Disease/May 1980 463