26 



PLASMODIOPHORALES 



of the host, gametes, zygotes, cysts, amoebae, pre- 

 plasmodia, and buds are formed. If conditions are 

 favorable, however, P. Brassicae does not develop 

 all of these phases. Jones' account has never been 

 confirmed, and most subsequent investigators have 

 doubted tlie accuracy of his observations. In light of 

 present-day knowledge about P. Brassicae it seems 

 likely that he may have been dealing with develop- 

 mental pliases of more than one organism. Milovidov 

 and Honig contended that some of the stages figured 

 bv Jones relate to Olpidiiim Brassicae and Asiero- 

 cystis radicis. 



P. BRASSICAE Woronin, I.e., pis. 1-6. 1878. Jahrb. Wiss. 

 Bot. 11: .548. Pis. :39-34. 



Resting spores globose, spherical 1.6-4.3 /x. aver- 

 age 3.9 jx, oval, ellipsoidal, 4.6X<3jU., sometimes 

 constricted, elongate and irregular, 2. .5-6. 9 /i, with 

 smooth, relatively thin, hyaline walls. Zoospores 

 pyriform, splierical, 2. .5-3.5 /it, swimming rapidly 

 and becoming intermittently amoeboid. Sporangial 

 Plasmodia variable in size. Zoosporangia few or nu- 

 merous, small, oval, spherical, 6-6.5 /^. angular and 

 elongate with thin hyaline walls : producing 4 to 8 

 zoospores which are liberated by the collapse of the 

 sporangium wall. Sporogenous plasmodia 100-200 /x 

 in diameter, hyaline to pale-grey in color, amoeboid; 

 encysting occasionally, undergoing schizogony into 

 uni- and multinucleate meronts. 



Parasitic in the roots of wild and cultivated cruci- 

 fers in temperate climates throughout the world, 

 causing spindle-shaped, globose and irregular swell- 

 ings, or galls and occasionally dark sunken spots and 

 lesions. 



A complete list of hosts, degree of infection, geo- 

 graphical distribution, and bibliography of P. Bras- 

 sicae are given in Chapter VI. 



Biological Races of Plasmodiophora Brassicae 



Marked differences in degree of infection have 

 been found in various species and varieties of wild 

 and cultivated crucifers, and this has led to the belief 

 that P. Brassicae may include several biological 

 races or strains which are more or less virulent and 

 specific for certain hosts. Appel and Werth ('10), 

 Ericksson ('13), Hostermann (according to Honig. 

 '31), and Gleisberg ('23) suggested the existence of 

 such races, and numerous attempts have been made 

 to demonstrate their jiresence. Between 1924 and 

 1929 Honig made six experiments involving a large 

 number of cruciferous liosts from which he ('31) re- 

 ported positive results. A strain of P. Brassicae from 

 kohlrabi was found to be readily transmissible to 

 kohlrabi, cauliflower, rape, turnips, and Cammelina 

 sativa, but could be transmitted only with difficulty 

 to radishes. A cauliflower strain was also discovered 

 which proved to be similar to the one on kohlrabi, but 

 strains from Savov cabbage and radish were found 

 to be distinct. Motte ('33, '35) and MacLeod ('31) 

 believed that they liad obtained evidence of biologi- 

 cal specializ.-ition, but later after making tests of 

 spores from 50 different sources, the latter worker 



found no evidence to confirm this belief. Motte ('33) 

 found that the form from charlock grew especially 

 well on turnips. Gibbs ('31) likewise tested various 

 inocula for evidence of specialization, but all of his 

 results were negative. In 1939 J. C. Walker observed 

 a high degree of resistance to club root in swedes in 

 Wisconsin, which was contrary to results obtained 

 elsewliere, and thought that this difference indicated 

 a variation in pathogenicity of the causal organism. 

 He accordingly secured spores from widely sepa- 

 rated regions of the United States and tested their 

 virulence on swedes, but found little difference in 

 pathogenicity.' The data in the literature on the ex- 

 istence of biological strains are therefore conflicting, 

 and most investigators, witli the exception of Honig 

 and ^Nlotte. liave doubted tlie presence of such strains 

 in P. Brassicae. 



1 However, in a paper presented before the Dallas, 

 Texas, meeting of the American Phytopathological So- 

 ciety, December, 1941 (Phytopath. S2: 18). Walker gave 

 additional data on physiological specialization in P. iJro.v- 

 .licae. Purple Top Milan turnip remahied completely free 

 of club root when grown in heavily infested soil in Wis- 

 consin, but when planted in naturally infected soil in Eng- 

 land, about -'0 per cent of the plants were diseased. On the 

 other hand, an English variety. White Stone, which showed 

 87 ))er cent infection in an English test, failed to develop 

 clubbed roots in inoculation tests with a representative 

 American isolate of P. Brassicne. Walker accordingly con- 

 sidered this evidence as proof of the existence of physio- 

 logical races. 



Bacteria in Relation to P. Brassicae 



The association of bacteria with P. Brassicae in 

 roots of diseased crucifers was noted by Eycleshy- 

 mer in 1894 and confirmed by Pinoy ('05). E. F. 

 Smith ('11). and other early workers. From his pre- 



PLATES 2, 3, 4 

 Pldsmndiofihorn Brassicae 



Fig. 1. Infected cabbage roots with spindle-shaped swell- 

 ings. Woronin, '78. 



Fig. -2. Beginning of club formation on roots of cabbage 

 inoculated experimentally. Woronin, I.e. 



Fig. 3. Heavily infected turni]) root. Woronin, I.e. 



Fig. 4. Cross section of infected cabbage root. Note two 

 compact groups of infected cells on lower right side, the 

 so-called "krankheitsherde." Woronin, I.e. 



Fig. 5. Nuclear division in an enlarged infected host cell. 

 Lutman. '13. 



Fig. (i. Division of infected cell. Lutman. I.e. 



Fig. 7. Enlarged cells of cabbage with mature plasmodia 

 showing the swelling and dissolution of intervening cell 

 walls. Hochlin, "33. 



Fig. 8. Normal host nucleus. Lutman, I.e. 



Fig. f)-\2. Enlargement, distortion, and degeneration of 

 liost nuclei in infected cells. Lutman, I.e. 



Fig. 13. Germination of resting spore. Chuiip, '17. 



Fig. 14, 15. Same. Woronin, I.e. 



Fig. l(i-18. Germination of resting spore, and amoebae. 

 Honig, '31. 



Fig. 19, Jl. .Amoeboid, anteriorly uniflagellate zoospores. 

 Woronin, I.e. 



Fig. JO. Fixed and stained zoospore with anterior blepho- 

 rophist. Cook and Schwartz, '30. 



