POTATO 'wart' 



711 



It is characterised by irregular warty or coralloid protuberances, 

 which grow from the eyes of the tubers and from buds on the 

 rhizomes below ground. The warts may be less than a small 

 pea in size, or as large or larger than the tuber on which they 

 grow. 



The diseased abnormal growths are due to the attack of a 

 parasite, Synchytrium endobioticum (Schilb.) Percl., which belongs 

 to the Chytridiacese, a group of organisms usually included 

 among the lower fungi. 



In a section cut through a piece of the warty tissue in autumn 

 the parasite is seen in the form of round sporangia or sporocysts 

 within the thin parenchymatous cells of the tissue. Each sporo- 

 cyst has a thick brown coat, on the outside of which are irregular 

 thickenings. Within is a thin transparent lining containing 

 hundreds of minute zoospores (Fig. 237A, i). 



Fig. Z37A I. Section through piece of ' warty ' tissue of potato showing thick-walled 



sporangia oi Synchytrium endobioticunu z. Sorus of three summer sporangia. 



In spring the outer coat of the sporocyst cracks and the 

 motile zoospores are set free through the opening. They are 

 able to swim about in drops of water, but after an hour or less 

 they become amoeboid (Fig. 237B), and when brought in contact 

 with the delicate tissue in the eye of a young tuber they penetrate 

 into the interior of the cells, where they grow and feed upon the 

 cell contents. The invaded cell for a time grows in size with 

 increasing growth of the parasite, but is finally destroyed and 

 the material within it largely consumed. The surrounding cells 

 are stimulated ; rapid division and growth occurs among them, 

 and a wart is soon produced. 



