592 



BACTERIA IN RELATION TO PLANT DISEASES 



Laboratory of Plant Pathology, Bureau of Plant Industry, United States Depart- 

 ment of Agriculture, under his direction, was the only one which devoted itself ex- 

 clusively to the study of bacterial diseases of plants. Three volumes by Smith, Bac- 

 teria in Relation to Plant Diseases, "^ and a later volume. Bacterial Diseases of Plants,^ 

 constitute the most notable contribution in phytobacteriology. A great deal of at- 

 tention was paid in Smith's laboratory to studies of crown-gall {Bact. tumefaciens), 

 with special reference to the nature and mechanism of tumor formation and the bearing 

 of these on the nature and mechanism of cancer in animals. The Department of Plant 

 Physiology and Pathology of the Imperial College of Science and Technology, London, 

 under guidance of Prof. S. G. Paine is publishing a series of "Studies in Bacteriosis."-* 

 Otherwise, the Hterature on phytobacteriology is scattered in journals and research 

 bulletins. 



DISTRIBUTION OF BACTERIAL PLANT PATHOGENS 



Practically all serious studies of bacterial diseases of plants have been concerned 

 with economically important plants. Non-cultivated plants are now being given con- 

 sideration as possible sources of inoculum.^ There has not yet been made a complete 

 survey of even the bacterial diseases of economic plants. The field is immense be- 

 cause of the large number of plants which are actually or potentially valuable eco- 

 nomically. It is continually growing because man, by selecting and developing new 

 varieties of plants, and by his persistent attempts to grow plants, or to transport or 

 store them or their parts, very often under conditions more or less unfavorable to the 

 plant, is continually creating possibilities of new host and pathogen relations. The 

 fact that the temperature of plants in the main roughly follows that of the air with 

 corresponding changes in metabolism renders them subject to attack by groups of 

 organisms with widely different requirements. 



While according to our present knowledge schizomycetes play a greater role in 

 animal diseases than do true fungi, their role as plant pathogens is subordinate. The 

 reason for this is not known. The inability of most fungi to grow well at 37° C. proba- 

 bly keeps down the number of fungi attacking animals. The preponderance of fun- 

 gous versus bacterial diseases of plants is surmised to be in part due to the inhibitory 

 action of acid cell sap on bacterial growth, and in part to the fact that bacteria, es- 

 pecially non-spore-bearing ones, are more subject to vicissitudes of environment than 

 fungi. Furthermore, fungi are better equipped structurally and functionally to effect 

 entry through the protective tissues of plants and when once in, to progress through 



the tissues. 



Smith,5 summarizing our knowledge relative to the distribution of bacterial dis- 

 eases in the plant kingdom, states: "It appears likely that eventually bacterial dis- 

 eases will be found in every family of plants from lowest to highest," basing this pre- 

 diction on the fact that while the field is relatively a new one, and there are no workers 



'Smith, E. F.: op. cit. (Washington, D.C.), Vol. i, 1905; Vol. 2, 1911; Vol. 3, 1914. 



» Smith, E. F.: op. cH. Philadelphia and London, 1920. 



3 Paine, S. G.: "Studies in Bacteriosis," II Ann. Appl. Biol., 5, 206-17. 1918. 



" Gardner, M. W. : "A Native Weed Host of Bacterial Blight of Bean," Phylopalh., 14, 341. 1924. 



s Smith, E. F.: Bacterial Diseases of Plants. 



