UNITED STATES DEPARTMENT OF AGRICULTURE 
DEPARTMENT BULLETIN No. 1465 
Washington, D. C. 
January, 1927 
A METHOD OF GROWING BACTERIOLOGICALLY STERILE POTATO PLANTS 
By H. G. MacMillan, Pathologist, Office of Vegetable and Forage Dis- 
eases, Bureau of Plant Industry 
CONTENTS 
Page 
Introduction 1 
The apparatus.. 2 
The cans and their covers. 2 
Soil-sterilizing kettle 4 
The boiler . 5 
Transportation of cans 5 
Electrical-resistance thermometer 5 
Aseptic culture house _ ._ 5 
The weighing frame and balance 6 
The watering machine 6 
Minor equipment 9 
Character of soil 10 
Methods and technique 10 
Filling the cans with soil 11 
Filling the kettle 11 
Sterilization 11 
Removing and sealing the cans 12 
Preparation of tape?, glue, varnish, etc... 12 
Preparation of culture media 13 
Page 
Methods and technique— Continued. 
Preparation of potato seed pieces 13 
Planting the seed pieces. 14 
Preparation of sterile water 15 
Supplying the cans with sterile water... 15 
Weighing the cans 16 
Testing the soil and water 16 
The experiment in operation 17 
Regarding soil sterilization 17 
Sources of contamination 18 
Loss of seed pieces 18 
Effect of soil sterilization 19 
Effect of temperature 19 
Keeping the weight of cans uniform 19 
Growth of plants 20 
Inoculation 20 
Results 20 
Discussion 21 
Conclusion 21 
INTRODUCTION 
Studies of different phases of the diseases of the potato (Solanum 
tuberosum) caused by Fusarium species were carried on from 1916 to 
1920. 
In the Western States the most serious fungous diseases of the 
potato are those which exist in the soil or develop and attack the 
plant through underground parts. To define precisely the disease 
symptoms on the potato caused by Fusaria or other soil fungi has 
long seemed impossible. The symptoms vary widely, with appar- 
ently like causes. A similar type of symptom was usually obtained 
in inoculation experiments, but it was desirable to obtain greater 
definition and precision in this respect. The most logical method in 
the solution of this difficulty appeared to be the development of 
plants free from organisms of all kinds, a bacteriologically sterile 
plant growing in sterile soil and in other respects as nearly as possible 
under field conditions. Given the pure culture of a potato plant, the 
symptoms resulting from the introduction of pathogenic organisms in 
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