67 



to serve as a basis in soil sterilisation research } and a method 

 for testing- immunity or susceptibility more rapidly than is at 

 present done in the field. Experiments on infection by the winter 

 sporangium in the soil have shown that a very high degree of 

 soil moisture is necessary to ensure infection, but this need not 

 be present during the whole of the growth period. It appears 

 most effective when the wet period is in the second month. A 

 high percentage infection is obtained in potato plants grown in 

 soils of very varying physical character. Under the conditions 

 of pot experiments the wart disease organism survives in the soil 

 in the absence of the potato plant for a period of at least a year. 

 There appears to be a dormancy period of about six weeks 

 between soil infection and sporangial germination. The relation 

 of numbers of sporangia in the soil to the incidence of disease 

 is discussed. When favourable conditions were maintained 

 80-100 per cent, of the plants tested were found to be infected 

 within a period of three months, even in varieties which in the 

 field appear least susceptible. Under conditions less favourable 

 to infection the relative susceptibilities of the several varieties 

 become clearly marked. No wart disease was found under any 

 conditions on immune varieties. Infection of various plants other 

 than the potato was attempted. Small warts were found on three 

 varieties of tomato and on Solatium nigrum and S. dulcamara, 

 but none on five other varieties of tomato, on Datura Stramonium, 

 Salpiglossis sinuata, Hyoscymus niger, Atropa belladonna, 

 Lycium chinense or on many common weeds grown in infected 

 soil. 



A method is described for infecting sprouting tubers with 

 wart disease by means of summer sporangia. Susceptible 

 varieties subjected to this treatment develop young warts within 

 three weeks, while immunes remain clean. The method can 

 therefore be used for testing immunity or susceptibility in the 

 laboratory. 



i 

 LVII. — W. A. Roach, Mary D. Glynne, Wm. B. Brierlev 

 and E. M. Crowther. " Experiments on the Control 

 of Wart Disease of Potatoes by Soil Treatment with 

 Particular Reference to the use of Sulphur/' Annals 

 of Applied Biology, 1925. Vol. XII., pp. 152-190. 



As susceptible varieties of potato are still widely cultivated 

 and sporadic outbreaks of wart disease are a serious menace, it 

 was imperative to find a method whereby the winter sporangia 

 of Synchytrium endobioticum in contaminated soil could be killed. 

 Previous studies and the unusual difficulties presented by the 

 problem are discussed. Results of experiments extending over 

 four years are recorded. 



During 1921-2 pot experiments were carried out to test 

 various chemicals both alone and in conjunction with steam. 

 Steaming the soil proved effective in eliminating the disease, but 

 it offered little hope of being economically possible as a field 

 treatment. The amount of disease was reduced by sulphur, 

 calcium and potassium polysulphides, formaldehyde, dichlor- 



