120 



PLASMODIOPHORALES 



He found that resistance was correlated with a low 

 sugar content in the cell sap and a pungent, bitter 

 taste of the expressed juice, while the cell sap of 

 susceptible plants was comparativel.v rich in sugar 

 content. Whitehead ('25), however, asserted that the 

 factor determining resistance is not related to total 

 dry matter or sugar in the roots. Further observa- 

 tions and experiments on the nature of resistance 

 were made bj- Rochlin in 1933, who tested i7 wild 

 and cultivated species belonging in 11 genera of the 

 Cruciferae for their susceptibility to P. Brassicae. 

 He found that the reaction varied from complete 

 immunity in some species to susceptibility in others, 

 independently of their taxonomic position, as Cun- 

 ningham had previously shown. All gradations of 

 susceptibility occurred in one and the same genus. 

 Rochlin also made a comparative anatomical study 

 of the roots of numerous species and found that in 

 the early stages of growth immunity or susceptibility 

 is not correlated with any marked differences in root 

 structure. In adult plants, however, the penetration 

 and spread of P. Brassicae is hindered to some de- 

 gree by the development of cork layers, collenchyma, 

 and by the compact structure of the wood layers. 



The degree of resistance exhibited by a species or 

 variety is directly correlated with tlie amount it con- 

 tains of those glucosides which on fermentation with 

 my rosin produce highly pungent mustard oils, ac- 

 cording to Rochlin. Chief among such glucosides in 

 crucifers are sinigrin (particularly abundant in B. 

 nigra and horseradish and in smaller amounts in 

 Sinapsis juncea, B. rapa, B. Napus, etc.), gluconas- 

 turtiin (in Barharea praecox and Nasturtium offi- 

 nale), glucotrapaeolin (in Lepidium sativum), etc.), 

 and glucocochlearin (in Cochleari officinalis). Sina- 

 blin, a glucoside present in B. alba, which does not 

 yield a pungent mustard oil, was found to be of no 

 protection against infection with P. Brassicae. 



An indication of the possible use of active gluco- 

 sides or their derivatives as fungicides is shown by 

 the results obtained by Rochlin in a small experi- 

 mental plot in which seeds of tlie very susceptible 

 Brunswick cabbage were sown in highly infected 

 soil in pots, some of which were abundantly watered 

 with a water extract from B. nigra seeds. Only 20 

 per cent of the seedlings became infected and showed 

 a very slight swelling of the roots, while all the con- 

 trol seedlings were infected. Considerable doubt has 

 been thrown on Rochlin's theory of the nature of re- 

 sistance by the subsequent studies of Walker ('36), 

 Walker, Link, and Marcell ('36). These workers 

 found that some collections of B. nigra are very sus- 

 ceptible and that there is no correlation between mus- 

 tard content and resistance. 



From the practical standpoint, Rochlin suggested 

 the possibility of controlling club root b}' crossing 

 cruciferous species deficient or meager in active glu- 

 cosides with those which contain greater amounts of 

 these substances. Pryor investigated this possibility 

 by direct experiments involving variation of the mus- 

 tard oil content of crucifers and noting their sus- 

 ceptibility to the disease. All mustard oils in cruci- 



fers contain sulphur and nitrogen, while their gluco- 

 sides also contain potassium. Thus, by lowering or 

 increasing these nutrient elements, it is possible to 

 change the mustard or sulphur oil content of experi- 

 mental plants. From the results obtained by this 

 procedure, Pryor concluded that sulphur oils do not 

 inhibit or prevent infection and development of club 

 root in crucifers — thus refuting the observations of 

 Rochlin.' 



Geographical Distribution of Club Root and 

 Bibliography of Literature 



Club root is now world wide in distribution, and 

 the countries from which it has been reported up to 

 the present time are listed below. The number of 

 publications on the occurrence, distribution, hosts, 

 life-history, cytology, relationships, eradication and 

 control of P. Brassicae and club root is quite large 

 and many of them are to be found in local journals 

 which are not readily available. In the bibliography 

 which follows many such publications have doubt- 

 less been overlooked and omitted. 



Alberts, H. W'. 1930. Rept. Alaska Agric. Exp. Sta. 



1930: 6. 

 Georgeson. 1914. Ibid. 191 i: 27. 1915, Ibid. 1915: 



39. 1917, Ibid. 1917: 8. 1919, Ibid. 1919: 21. 



1927, Ibid. 1927: 10. 



ARGENTINA 



Marcliionatto, J. B. 1929. Phys. Rev. Soc. Argentina 

 deCien. Nat. 9:455. 



AUSTRALIA 



Anony. 1940. Agr. Gaz. New South Wales 51: 559. 

 Darnell-Smith, G. P. 1924. Agric. Gaz. New S. 



Wales 35: 180, 488. 

 McAlpine, M. D. 1898. Proc. Linn. Soc. N. S. Wales 



1898: 82. 



. 1901. Dept. Agric. Victoria 1901. 



. 1903. Dept. Agric. Victoria 1903. 



Noble, R. J. Intern. Bull. PI. Protect. 5 : 202. 

 Stubbs, L. L. 1941. Jour. Dept. Agric. Victoria 39: 



208. 



AUSTRIA 



Anonymous. 1933. Bundesant. f. Pflanzensch. Mit- 



teil. 167. 

 Kock, G. 1911. Landesamtbl. Erzherogtums Osterr. 



a. d. Enns 1911, no. 1. 

 Kornauth, K. 1913. Zeitschr. Landw. Versuchsw. 



Osterr. 17:395. \915, Ibid. 19: 180. 



1 In a paper presented before the December 29, 1941, 

 meeting of the American Phytopatholofjical Society, 

 Dallas, Texas, W. J. Hooker (see Phytopathology 32: 9) 

 reported that two mustard oils (alhi isothiocyanate and 

 beta phenyl ethyl isothiocyanate) were consistently effec- 

 tive in preventing spore germination at 80 ppm. and some- 

 times at as low concentrations as 10 ppm. of allyl isothio- 

 cyanate and 5 pi)m. of beta phenyl ethyl isothiocyanate. 

 Concentrations of both oils below the toxic level were found 

 to be capable of stimulating spore germination. 



