1 64 Diseases of Truck Crops 



tive portion known as "mycelium" which, when 

 young, is hyaline, but which becomes gray with age. 

 Whether young or old, they are capable of breaking 

 up into as many cells as there are septa, and each cell 

 may assume the function of a spore, since it will 

 readily germinate. In another stage, chains of 

 hyaline spores are born and pushed out from within 

 long terminal cells of the mycelium. The chlamy do- 

 spores apparently serve as resting spores to carry the 

 fungus over winter, and the cells of the infected tissue 

 are usually filled with these brown thick-walled spores. 

 A last stage is that of pycnospores which are born 

 within long-necked spore sacks called pycnidia (fig. 

 26 c). These are minute globular spores oozing out 

 in a gelatinous mass which stick to the open end of 

 the long neck of the pycnidium. In pure cultures 

 the spores ooze out in strings just as in the case 

 of certain species of Phoma or Phyllosticta. The 

 spores can germinate in water or in any nutritive 

 fluid. 



Phyllosticta Leaf Blight 



Caused by Phyllosticta batatas E. and M. 



Leaf blight appears as roundish to angular spots 

 on the upper side of the leaf and is separated from 

 the healthy tissue by a dark line. Inside this line is 

 a strip of brownish tissue which has lost most of the 

 green color. Within this ring is a circular area much 

 lighter in color in which the pycnidia are found 



