Experiment Station Record, Volume 92, January-June, 1945 Page: 73
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1945] DISEASES OF PLANTS 73
Chalara quercina n. sp., the cause of oak wilt, B. W. HENRY. (Wis. Expt.
Sta.). (Phytopathology, 34 (1944), No. 7, pp. 631-635, illus. 1).-The causal
fungus of the wilt attacking Quercus alba, Q. borealis, Q. coccinea, Q. macrocarpa,
and Q. velutina in Illinois, Iowa, Minnesota, and Wisconsin is described as
C. quercina (see following entry).
Oak wilt: Its significance, symptoms, and cause, B. W. HENRY, C. S. MOSES,
C. A. RICHARDS, and A. J. RIKER. (Wis. Expt. Sta. coop. U. S. D. A;).
(Phytopathology, 34 (1944), No. 7, pp. 636-647, illus. 2).-This destructive oak
disease-studied in Wisconsin and neighboring States-has appeared widely distributed
and its presence has been confirmed by positive culture work in 23 counties
of Wisconsin, 5 of Minnesota, 2 of Iowa, and 1 of Illinois; it appears to be the
most important oak disease in the Upper Mississippi Valley. No correlation was
found between site and occurrence. Red and black oaks were the most common
hosts and, once attacked, have not been known to recover. Two wilting scarlet
oaks were found; white and bur oaks were also attacked but seemed relatively
The first symptoms are slight crinkling and paling of the leaves, often followed by
a progressive bronzing to browning of the leaf blade from the lateral edges and
apex toward the midrib and base; mature leaves remain relatively stiff, but young
leaves droop conspicuously. Defoliation varies in extent and seemingly occurs at
any symptom stage on mature leaves. Affected young leaves remained attached
after wilting. Symptoms usually progress over the entire tree within a few weeks.
Secondary foliage often appears along the trunk and larger branches, but this in
turn wilts and dies. Discoloration in the sapwood of twigs was found in numerous
cases but is not diagnostic. A fungus, tentatively placed in the genus Chalara, was
isolated from 116 of 122 wilt trees sampled but was not obtained from any 6f 56
nonwilt trees. Stem inoculations and reisolations were successful on 74 of 90 woodland
trees, cultures from 8 locations in Wisconsin being used.
Measuring the local distribution of Ribes, S. B. FRACKER and H. A. BRISCHLE.
(U. S. D. A.). (Ecology, 25 (1944), No. 3, pp. 283-303, illus. 9).-Observations
on the local distribution of Ribes in three locations of northern Idaho and eastern
Washington and in two of California are reported. The Ribes in four of the locations
were distributed locally as if a "contagious" distribution were superimposed on
a random "Poisson" distribution in the proportion of about 2 to 1; in one of the
California plats the proportion was about 3 to 2. This plan of distribution is consistent
with the biology of Ribes, and the authors propose the term "mixed" distribution
to describe it. If s represents the size of each block in acres, c the percentage
of check (in this case either 4 or 8), and r the Ribes per acre, the product of the
three, scr, represents the Ribes population per 100 quadrats. The fact that any
given value of the products s X c X r shows substantially the same percentage, i,
of occupied quadrats, regardless of the percentage of check or the size of quadrat, is
of practical significance to the problem of checking the blister rust-control projects.
It indicates that increasing the percentage of check renders possible a proportionate
decrease in either the unit size of the plat or the minimum. Ribes-population class
about which information is desired.
Divergence from the random type of divergence can be measured by a distribution
factor, D, since such a divergence tends to follow the relationship scr = Dn,
where n is the mean number of Ribes per 100 quadrats that would be expected in
the case of a strictly random distribution in which the observed percentage, i, of
the quadrats were occupied. A Poisson transformation can be used to bring the data
into this rectilinear form for analysis of variance. Where curvilinearity is apparent,
divergence can be measured by the d factor in, the equation scr i n + dn2.
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U.S. Department of Agriculture. Agricultural Research Administration. Office of Experiment Stations. Experiment Station Record, Volume 92, January-June, 1945, book, 1947; Washington. (digital.library.unt.edu/ark:/67531/metadc5064/m1/86/: accessed February 19, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.