CHAPTER XLIV 

 BACTERIA IN RELATION TO PLANT DISEASES 



GEORGE K. K. LINK 



University of Chicago 



Present activity in the field of bacterial diseases of plants may be divided arbi- 

 trarily into three categories. The first consists of survey work, i.e., the discovery, 

 diagnosis, and description of new diseases and their pathogens; determination of the 

 host range, method and source of infection, and control of the new pathogens. The 

 second, which is to a great extent incidental to or necessitated by the first, consists 

 of a more detailed restudy of pathogens which have been generally accepted in phy- 

 topathological literature. The third consists largely of incidental or isolated explora- 

 tory studies of general biological aspects of plant bacteriology. These include studies 

 of life cycles of bacteria, testing of the validity of species identification, and of estab- 

 lished systems of classification, studies in infection, virulence, immunity-suscepti- 

 bility phenomena, serological properties of pathogens, and detailed study of the 

 phenomenon of gall formation in crown gall. The relatively late introduction of 

 Koch's method and the small number of workers have left room, even now, for sur- 

 vey and pioneer work in phytobacteriology. 



HISTORICAL DEVELOPMENT 



Although a series of observations and experiments by botanists, culminating in 

 the classical work of De Bary on the smut and rust fungi (1853), had conclusively 

 demonstrated the association of fungi with diseases and the nature of parasites and 

 infection and De Bary's brilliant researches on the fungus of the late blight of the 

 potato (1861-63) had conclusively established the causative role of a definite micro- 

 organism, Phytophthora infestans, in a specific disease, these researches apparently did 

 not affect the main current of experimentation and of speculation as profoundly as 

 the work of Pasteur and Koch. With the work of these men, especially that of Koch in 

 establishing the science of bacteriology, leadership in the study of infection and dis- 

 ease definitely passed to the animal field. 



While study of the role of bacteria in animal diseases progressed by leaps and 

 bounds, work in phytobacteriology was slowly getting under way. To be sure, there 

 were studies made in the field, but these, as other bacteriological studies up to Koch's 

 presentation of conclusive evidence that a definite bacterium was the cause of specific 

 disease, consisted of congeries of very important but incomplete observations and ex- 

 periments. Woronine in 1866^ had discovered bacteria in the root tubercles of le- 

 gumes, and Davaine in 1868^ had inoculated plant tissues with bacteria and obtained 



'Woronine, M.: "Ueber die bei der Schwarzerle {Alniis gliitinosa) und bei der gewohnlichen 

 Gartenlupine {Ltipinus miUahilis) auftretenden Wurzelanschwellungen," Mem. de VAcad. Imp. de St. 

 Pelersboiirg (7th ser.), 10, No. 6. 1866. 



= Davaine, C. R.: "Recherches physiologiques et pathologiques sur les Bacteries," Cow/)/, rr;;^. 

 liehd. des stances de I' Acad, des scL, 46, 109-503. 1868. 



S90 



