513 



THE AGRICULTURAL NEWS. 



September 28, 1912. 



FUNGUS NOTES. 



CROWN GALL OF PLANTS AND 



ITS RELATION TO ANIMAL 



CANCER 



In February 1911 there was issued Bulletin 213 of the 

 Bureau of Plant Industry of the United States Department 

 of Agriculture entitled Crown-Gall of Plants: Its cause and 

 Kemedy, by Erwin F. Smith, Nellie A. Brown, and C. O. 

 Townsend, and in June of this year appeared Bulletin 25.5 

 of the same Bureau under the title The Structure and 

 Development of Crown-Gall: A Plant Cancer, by Erwin 

 F. Smith, Nellie A. Brown and Lucia McCulloch. The 

 contents of these two bulletins are of very great interest, not 

 onh' because they provide a clear proof of the cause of crown 

 gall in plants — a disease that had baffled the numerous 

 earlier attempts to discover its origin; but even more perhaps 

 on account of the theory of the senior author that the structure 

 and development of these galls is analogous to those of cancer 

 growths in animals, and that the elucidation of the cause of 

 the one may result in the discovery of a similar cause for 

 the other and necessitate the acceptance as a fact of the now 

 much discredited theory that animal cancer is due to a bac- 

 terial parasite. 



Crown galls are hard or, more usually, fairly soft 

 swellings of varying sizes and unlimited growth that occur on 

 the crown, roots, stems and leaves of a comparatively large 

 number of different plants mostly of importance as crops or 

 ornamental plants. The duration of the galls depends 

 somewhat upon whether they are hard or soft, as in the 

 latter case they may be entered by saprophytes and secondary 

 parasites which destroy them; the entrance of these organisms 

 and of water is facilitated by the fact that the galls are usually 

 not protected by a cork layer on the outside. Another 

 disease often associated with the presence of galls is hairy 

 root in which a large number of roots, usually fine and hairy 

 but sometimes tteshy, arise at a small spot on an older root. 

 The spot usually consists of a Hat swelling similar in origin 

 and appearance to a small gall. This disease has been 

 shown bj' the workers mentioned to be due to an organism 

 very similar to that causing crown gall, and capable of 

 producing tumours only, when inoculated into plants. In one 

 instance both tumours and hairy root resulted from separate 

 inoculations with this organism on the same plant. Further 

 evidence of the identity of the two diseases lies in the fact 

 that occasionally hard galls are found in nature with a tuft of 

 small roots attached to them. Hard and soft galls were at 

 one time supposed to be different, but as the organisms 

 causing them are almost identical, and as numerous transition 

 forms between the two types of gall occur, they must now be 

 regarded as identical and the difference in their appearance 

 as due only to different rates of growth or to differences 

 in the tissues originally infected. Thus hard and soft galls 

 and hairy root are all to be regarded as of practically the 

 same nature and of nearly identical origin. 



Crown gall has been known in Europe on several 

 plants for at least fifty years, and has usually been ascribed to 

 frost or mechanical injuries. A few authors have attributed 

 it to bacteria, but without sufficiently conclusive proof. It 

 is particularly well-known on the grape, and occurs also on 

 the rose, poplar and probably peach, as well as other 

 plants. It has been recorded on the grape in Chile and 

 Peru, for South America, and on a large number of hosts 

 including the daisy, almond, peach, quince, apple, raspberry. 



blackberry, rose, grape, red clover, alfalfa, cotton, hop and 

 sugar beet, all over North America, while a similar disease on 

 poplar, willow, peach, apple and other trees is reported from 

 South Africa A disease that may well be the same has 

 been found on roses in the West Indies. 



The first results of the attempts made by Dr. Smith and 

 his fellow workers to isolate a causative bacterium from gall 

 tissues were all entirely of a negative nature, as of the 

 numerous different organisms obtained, none would reproduce 

 the disease when inoculated into healthy plant tissues. 

 Finally, however, it was observed that in cultures from daisy 

 tumours certain colonies developed some time after the others, 

 not until five or six days had elap.sed, and that when these 

 colonies were isolated in pure cultures, the bacteria compos- 

 ing them did cause galls when inoculated into healthy daisy 

 stems After this it was found that the same organism 

 could give rise to galls on several other plants on which such 

 swellings had been found in nature. The bacterium thus 

 isolated was studied on various culture media, its staining 

 reactions determined, and finally na.med Bacterium tumejanens. 

 Other very similar organisms were isolated from galls both 

 hard and soft, on several different host plants, as well as 

 from the swollen pad from which hairy roots arise. 



These organisms' all behaved in a more or less similar 

 manner on the different culture media and all produced galls 

 on the hosts similar to those from which they were isolated, 

 as well as on a more or less wide range of other plants. 

 Thus by inoculation, cross-inoculation and cultural methods 

 it was established that crown galls and hairy root on a large 

 number of different plants are due to different strains 

 of the same bacterium or to a very closely related group of 

 similar bacteria. 



The organism is a wound parasite that lives in the 

 soil, and in nature usually makes an entry through 

 wounds on the roots or crown. The amount of damage 

 caused by the galls varies on different hosts, but their presence 

 often results in the gradual death of the plant, and usually 

 causes stunting and barrenness even where death does not 

 occur. The disease is very common on nursery stock, 

 and it is by the distribution of infected plants that it is 

 principally disseminated. Smith urges the careful control of 

 such stock, and suggests that infected land should not be 

 replanted with plants known to be susceptible to the disease. 

 In hot houses it can be got rid of by heating the soil. 

 Continued inoculation experiments showed that the bacteria 

 lose their virulence when kept for some time — about two 

 years in this case — in pure cultures, and that different strains 

 isolated from different ho.'^t species, and from the same ho-st 

 species at different times, vary very considerably in their 

 virulence, some being apparently unable to reproduce the 

 disease at all. Further, it appeared that a certain degree of 

 immunity may be obtained in a strain of pliMrs reproduced 

 vegetatively when the strain is inoculated iinough several 

 generations. 



The primary tumours, such as are caused by inoculation, 

 originate as a rule in young growing tissue, generally the 

 cambium; they can only be successfully induced artificially 

 by inoculation into young, vigorou.sly-growing parts of the 

 host. When formed in the stem they include in their 

 substance elements of all or nearly all the usual tissues. 

 These primary tumours form (root or tumour) strands that 

 run through the normal tissues and may extend for some 

 distance; these consist of undifferentiated young cells that can 

 give rise to medullary rays, tracheids and sieve tubes, and 

 their cells are rich in chloroplasts. These strands can 

 become the origin of secondary tumours within the plant, 

 often situated at some distance from the original gall. 



