August, 1945 



Carter: Wetwood of Elms 



423 



whereas P. ligjiicola does not produce gas 

 from glucose, the only source of carbon 

 tested by Westerdijk & Buisman. In addi- 

 tion, it has peritrichiate, not polar, flagella, 

 coagulates litmus milk with the production 

 of acid, reduces nitrates, and does not 

 hydrolyze starch. Because of these differ- 

 ences, as well as because of the complex 

 type of disease it produces in elms, the 

 wetwood organism is believed to be a new 

 species and is so described below. It is 

 associated with the production of wet- 

 wood, wilt, dieback, premature leaf drop 

 and flux of elm — American, Littleford, 

 Moline, slippery, English and Siberian. 

 Affected trees flux through trunk wood 

 exposed by the removal of branches, 

 through cracks in crotches, cracks in 

 trunks, and other types of injuries that 

 penetrate to wetwood-al¥ected tissues. The 

 organism inhabits mainly heartwood and 

 inner sapwood and is especially likely to 

 invade elms through pruning wounds, 

 crotch injuries and wounds made during 

 surgical treatment, transplanting and 

 cultivation in the nursery. The wetwood 

 organism was isolated from dark brown 

 diseased trunk sapwood and heartwood 

 and occasionally from brown-streaked 

 branch wood. 



Erwinia nimipressuralis* New Species 



The organism is a short rod with rounded 

 ends, 0.68-2. 00X0.34-0. 68m, mostly 0.68-1.35 

 X0.34— 0.68^, arranged singly or, rarely, in 

 pairs or chains; motile, with up to six peri- 

 trichiate flagella; capsules and spores not 

 observed ; anaerobic, Gram-negative and not 

 acid-fast. 



On potato dextrose agar, colonies are cir- 

 cular, smooth, entire, flat to slightly raised, 

 and usually opaque (whitish cream). Growth 

 in streaks on potato dextrose agar is spreading, 

 glistening, whitish cream and viscid. Growth 

 in stabs in potato dextrose agar is abundant, 

 with liberation of gas. In nutrient broth, 

 growth is abundant with a thin pellicle or 

 flocculent surface growth, and sediment is 

 scant and viscid. In gelatin stabs, growth is 

 beaded and most abundant near the surface, 

 and the medium is unchanged. Gelatin is not 

 liquefied ; nitrates are reduced to nitrites 

 without the formation of gas; hydrogen sulfide 

 is formed ; no indole is formed ; starch is not 

 hydrolyzed ; pectin is not fermented ; milk is 

 coagulated ; litmus and bromocresol purple 

 are reduced. Methyl red and Voges-Proskauer 



*Etymology: L.-itin; nimis^Xoo much; pressnralis^= 

 perl.iining to pressure; literally, pertaining to too mucli 

 pressure. 



tests are positive. Optimum temperature for 

 growth, 24—30 degrees C, maximum 37 degrees 

 C, minimum 5 degrees C. or lower ; thermal 

 death point, 45—55 degrees C. Optimum pH 

 for growth, 6.82—7.50, maximum pH 10.00 + , 

 minimum pH 4.67. 



The organism produces both acid and gas 

 from arabinose, rhamnose, xylose, dextrose, 

 fructose, galactose, mannose, lactose, maltose, 

 trehalose, melibiose, cellobiose, mannitol, sor- 

 bitol and salicin ; slight acid and gas from 

 starch ; no acid or gas from inulin, dextrin or 

 filter paper; variable results from sucrose, 

 raffinose, melezitose, dulcitol, glycerol and elm 

 sawdust. 



The organism is pathogenic in trunk wood 

 of elms, Ulmus americana L., U. pumila L., 

 U. fulva Michx. and U. proccra Salisb. 



Inoculations 



Inoculation experiments were started in 

 1940 to determine the pathogenicity of the 

 bacterial isolates obtained from diseased 

 elms in Hinsdale that wilted in 1939. Two 

 hundred nine inoculations were made on 

 opening buds, leaves, shoots, branches, 

 trunk phloem, trunk cambium and trunk 

 current-season wood of American elms in 

 our experimental nursery. None of these 

 inoculations produced what were believed 

 to be typical infections or resulted in wilt. 

 Limited browning in trunk wood was 

 produced in inoculated heartwood and 

 older sapwood but was not at first believed 

 to represent infection. However, later ex- 

 periments showed this browning in trunk 

 wood to represent infection and early 

 development of wetwood. Patch grafting 

 of discolored inner bark from diseased 

 elms in Hinsdale on 28 healthy American 

 elms in our experimental nursery did not 

 produce infection or cause wilt. 



American Elm, Greenhouse Inocu- 

 lations. — Eight American elms, 1.0—1.5 

 inches d. b. h., grown in a greenhouse pit, 

 were used for this experiment, begun in 

 1941. Six of the trees were inoculated 

 with Erwinia nimipressuralis by use of a 

 hand syringe, fig. 23 — three on July 21 

 and three on August 5. Each tree was 

 inoculated by injecting 50 ml. of bacterial 

 culture in nutrient broth plus dextrose 

 into the trunk through a three-quarter- 

 inch hole. In each trunk the injection hole, 

 about 14 inches above the ground, was 

 bored at a downward slant and it extend- 

 ed three-fourths of the way through the 

 trunk. Each injection hole was closed with 



