6l6 MICROBIAL DISEASES OF PLANTS 



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 Biown and Ja.Tcdeson,* Pseudomonas aptatum, 

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

 rare; no spores or capsules observed; pseudozoogloese 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 1°; 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 of Intection. — It is beheved 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 C, "A Bacterium Causing a Disease of Sugar-beet and 

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



