Experiment Station Record, Volume 74, January-June, 1936 Page: 56
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56 EXPERIMENT STATION RECORD [Vol. 74
no less than from 0.1 to 1 mg per cubic centimeter. Since crude tobaccomosaic
sap diluted to 1-1,000,000 gives about one necrotic lesion per leaf on
Niootiana glutinosa and about 0.1 cc of sap dilution is used for the inoculation,
and assuming W. J. Robbins' hypothesis of 100,000 for the molecular weight of
the virus to be correct, it would follow that 1 cc of virus sap contains from
6.06X101" to 6.06X1015 virus molecules and that a single minimal infective dose
on this host corresponds to from 60,000,000 to 600,000,000 molecules of virus
antigen. Possible reasons for this enormous ratio of molecules to a single
Infection are noted.
Factors influencing the activity of tobacco mosaic virus preparations,
A. W. PETRE (Contrib. Boyce Thompson Inst., 7 (1935), No. 1, pp. 19-28, figs. 2).In
the procedure previously published by C. G. Vinson and the author2 for the
purification of tobacco-mosaic virus a pigment-free preparation was obtained
from the juice of diseased plants by preliminary precipitation with basic
lead acetate. In the supernatant liquid the virus was thrown out by neutral
lead acetate, and from the latter precipitate pigment was removed by M/3
monopotassium phosphate pH 4.5. From this pigment-free precipitate the
virus was removed by M/15 phosphate buffer pH 6.5.
As a result of studies here presented the following improvements in the
method are suggested: In the preliminary elution, increasing the concentration
of potassium acid phosphate assisted in removing the pigment, and increasing
the acidity of this buffer increased the activity of the virus removed in the
final eluate but was less effective in removing the pigment. In the final elution,
the lead acetate precipitates from the juice of field-grown tobacco plants
required an alkaline phosphate buffer of higher pH than 6.5 to demonstrate
their full activity. Favorable elution bvas obtained at pH 7.5 and 8.4.
Tobacco plants grown in glass cages proved less susceptible to infection with
tobacco mosaic than those grown in the greenhouse. The increased succulence
of the cage-grown plants is presumed to account for the differences in susceptibility.
The rate of leaf expansion was found not to be a factor in susceptibility.
Stem rot of tobacco caused by Sclerotinia sclerotiorum (Lib.) De Bary,
K. F. KHESWALLA (Indian Jour. Agr. Sci., 4 (1934), No. 4, pp. 663-673, pls. 4).A
serious stem rot of tobacco in Rangpur, Bengal, proved to be due to S. sclerotiorumn.
The disease symptoms, history of the pathogen, and control measures
are discussed. Studies of the pathogenicity, physiology, and cultural characters
of the fungus gave the following results:
Infection takes place on wounded stems and through the roots, and can be
induced by whole or cut sclerotia on wounded stems, as well as by ascospores
on wounded leaves.
In culture, optimum growth occurred at from 20' to 25 C., and growth
ceased at 30. In media rich in nutrients microconidia developed only after
the available food supply had been exhausted, and in nutrient-deficient media
in a short time.
The fully matured asci and paraphyses of the perfect stage were found.
Low temperature proved essential to the development of the apothecial stalks
and light for their expansion into disks. No Botrytis stage was observed.
Pleospora rot of tomatoes, G. B. RAMSEY (Jour. Agr. Res. [U. S.], 51
(1935), No. 1, pp. 35-43, pis. 2, fig. 1).-Pleospora rot occurs in California
tomatoes shipped in November and December and in Mexican tomatoes mar.
keted during January. The inciting organism (P. lycopersici) and its conidial
stage (Macrosporium sarcinaeforme) are usually both present on decaying
Mosaic disease of tobacco.-II, Activity of the virus precipitated by lead acetate.
Contrib. Boyce Thompson Inst., 3 (1931), No. 1, pp. 131-145.
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A topical, alphabetically arranged index to volumes 71-80 including experiment station records, publications reviewed, and foreign publications. In has a list of all editorial notes from the referenced volumes.
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United States. Office of Experiment Stations. Experiment Station Record, Volume 74, January-June, 1936, book, 1937; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc5082/m1/76/?rotate=90: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.