Infection experiments with wart disease of potatoes Synchytrium endobioticum (schilb.) perc

SUMMARY. A study of certain conditions controlling infection of potatoes by the winter sporangium of Synchytrium endobioticum in the soil and by the summer sporangium in the laboratory has been made with a view to finding a reliable method of pot experiment 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 experiment 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 Solanum nigrum and S. dulcamara, but none on five other varieties of tomato, on Datura Stramonium, Salpiglossis sinuata, Eyoscyamus 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.