626 MICROBIAL DISEASES OF PLANTS 



The melons should be supplorted by some means to keep, them from 

 coming in direct contact with the soil, and should be supplied with 

 adequate water during a dry season to keep them from cracking. 



I Soft Rot of the Sugar Beet 



Bacterium teutlium—M.eic&]i 



History.— A soft rot of the sugar beet, occurring in Nebraska, has 

 been described by Metcalf and Hedgcock.* 



Symptoms. — Beets affected with the rot show the lower half badly 

 decayed and honeycombed with "pockets" or cavities filled with a 

 sUmy, stringy fluid, colorless, sour-smelling, and alive with bacteria. 

 The vascular bundles remain intact, while the tissue surrounding them 

 is usually consumed. Above ground the beets appear normal. 



Method of Infection. — The germs gain entrance to the beet 

 through wounds and abrasions in the skin, and there is good reason for 

 believing that nematodes are responsible for many of the inoculations. 



Causal Organism. — Bacterium teutlium, according to Metcalf, possesses the 

 following characteristics: 



It is a short, non-motile rod, rounded ends, i.sm by 0.8/x; neither capsules nor 

 endospores have been observed; the organism stains readily with the aqueous 

 stains. Gram-positive. 



On nutrient agar, slow, scant, translucent, porcelain white, non-viscid, and pene- 

 trates the agar. On cane-sugar agar growth more rapid, viscid, watery, vitreous to 

 translucent, colorless. Gelatin stab — scant, filiform to beaded, dirty white, no 

 liquefaction. Cane sugar gelatin — characteristic cumulus cloud appearance in 

 stab, no liquefaction. Nutrient broth — slight clouding and sediment, acid pro- 

 duced. No evidence of growth in milk. No visible growth on potato. On carrot, 

 clear, viscid and acid. On sugar beet, viscid, clear, spreading, copious, acid, 

 parenchyma destroyed leaving vascular tissue. No growth in Uschinsky's, Fermi's, 

 Pasteur's, Fraenkel's or Dunham's solution. No gas from dextrose, saccharose, 

 etc. Facultative anaerobe. No growth at 37°. Optimum temperature, 17°. 

 Thermal death-point, 45°. 



CoNTROL.^The rot is less apt to be serious if the beets are grown on 

 relatively dry soil and if rotation of crops is practiced. The selection 

 of resistant varieties seems to be the most practical solution of the 

 problem. 



* Metcalf and Hedgcock, "A Soft Rot of the Sugar Beet," 17th Annual Report, Nebraska 

 Agr. Exp. Sta., pp. 69-112, 1904. 1 



