STEM LESIONS CAUSED BY EXCESSIVE HEAT 
By Carl Hartley 
Pathologist , Investigations in Forest Pathology , Bureau of Plant Industry , United 
States Department of Agriculture 
WHITESPOT INJURY 
During work on the damping-off disease of pines (Finns spp.) in 1909 
the writer noticed in a nursery at Halsey, in the Nebraska sand hills, a 
type of disease closely corresponding to the old published descriptions 
of damping-off. The stems of very young seedlings developed shrunken 
areas at the soil surface. Commonly the entire stem was constricted by 
the lesion, the seedling fell over, and died. The writer has previously 
referred to this type of injury as “whitespot” (4, p. 5). 1 Close exami¬ 
nation showed that this trouble differed in several ways from the type 
of damping-off which the writer and assistants have produced by inocula¬ 
tion with common pine-seedliflg parasites ( Pythium debaryanum Hesse, 
Corticium vagum B. and C., and species of Fusarium). The primary 
whitespot lesions were in all cases limited to the stems, and usually just 
above the ground line. The whitespot lesion is very light in color, and 
this characteristic color continues to the very edge, making a sharp line 
of demarcation from the healthy tissue. Lesions may continue defi¬ 
nitely limited for some days, and the upper stem and cotyledons remain 
turgid. In this early stage most cases of whitespot injury are easily 
distinguished from damping-off. Typical damping-off in porous soils is 
primarily a rootrot, which may attack above the ground line, but which 
more commonly attacks below. Damping-off lesions caused by any of 
the above-mentioned fungi or by Botrytis cinerea vary in color at dif¬ 
ferent stages, gradually shading into the tissue still unaffected, and 
progress continuously both upward and downward. 
This whitespot injury was at first supposed to be merely a special 
type of damping-off. Cultures made from the whitespot lesions failed 
to develop regularly any recognizable parasites, while most of the parallel 
cultures from lesions of the rootrot type yielded Pythium debaryanum . 
Alternaria sp. was the only fungus commonly obtained from the white 
spots. 
Further examination showed that, in cases where whitespot lesions 
affected one side of the stem only, it was nearly always the south or 
southwest side. On seedlings which had been girdled, the lesions, if at 
all asymmetrical, extended higher on the south than on the north side. 
The south margins of the seed beds, imperfectly protected by the shade 
1 Reference is made by number (italic) to Literature cited,” pp. 603-604. 
Journal of Agricultural Research, 
Washington, D. C. 
pl 
( 595 ) 
Vol. XIV, No. 13 
Sept. 23, 1918 
Key No. G-156 
