LEAF SPOTS 977 



Microscopic examination of the diseased spots and adjacent area shows 

 the tissue to be filled with a large number of active bacteria. Sections 

 cut from the central portions of the diseased areas show the cell walls 

 to be ruptured or collapsed, while the cells bordering the ruptured 

 places show that the bacteria are in the cells. The disease is repro- 

 duced readily with typical symptoms by means of needle prick inocula- 

 tions with pure cultures. So far as has been observed, the causal 

 organism does not attack the beet root, but is confined strictly to the 

 beet leaf. 



CAUSAL ORGANISM. According to Brown and Jamieson, * Pseudomonas aptalum, 

 n. sp., is a short, motile rod with rounded ends; flagella, bi-polar; involution forms 

 rare; no spores or capsules observed; pseudozoogloeae occur; aerobic; smooth whitish 

 colonies on agar plate with fish scale-like markings; clouds beef bouillon in eighteen 

 to twenty-four hours; produces alkaline reaction in litmus milk, with a gradual 

 separation of whey from curd; liquefies gelatin; produces ammonia; no reduction 

 of nitrates; fluorescence greenish; no diastasic action on potato starch; grows in 

 Uschinsky's and Fermi's solutions; indol produced after ten days; optimum 

 temperature 27 to 28; maximum 34 to 35; minimum i; thermal death- 

 point 47.5 to 48; vitality four to ten months in beef agar, ten to twelve months 

 in beef bouillon, depending on temperature; growth good on litmus-lactose agar; 

 growth much retarded on gentian violet agar; stains readily with basic anilin dyes; 

 not acid fast; not stained by Gram; tolerates acids; oxalic o.i per cent; tartaric 

 0.2 per cent; hydrochloric o.i per cent; tolerates sodium hydroxide in beef 

 bouillon, 18 Fuller's scale; no growth in Cohn's solution; killed readily by drying; 

 not very sensitive to sunlight; retains its virulence two to three years. 



PATHOGENESIS. Pathogenic to nasturtium and sugar-beet leaves; 

 spots have been produced by artificial inoculations on leaves of pepper, 

 lettuce, egg plant, and upon the leaves and pods of the bean plant. 



METHOD or INFECTION. It is believed that infection takes place 

 only in bruised or wounded tissue, due to insects or to mechanical injury. 



CONTROL. No practical methods of control have been undertaken. 



* Brown, Nellie A., Jamieson, Clara O., "A Bacterium Causing a Disease of Sugar-beet and 

 Nasturtium Leaves," Jour. Agr. Res., Vol. I, No. 3, p. 189, 1913- 



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