Apr. IS. I9IS Phoma Destrtictiva 13 



DESCRIPTION OF THE FUNGUS ON ITS HOST 



CHARACTER OF SPOTTING 



The Phoma fungus produces spots on green and on ripe tomato fruit 

 and on tomato leaves. The fruit, so far as observed, becomes infected 

 only through wounds, while infection of the leaves and stems may be 

 produced without w^ounding by means of spore spraying. The spots 

 on ripe tomato fruit are black, carbonaceous, definite in outline, and 

 have the surface covered with small black pycnidia. Surrounding the 

 dark tissue of the spot is a watery-looking zone. Frequently the tissue 

 breaks, and a grayish white mycelium develops in the cracks. The 

 spots produced upon green fruit vary from brown to black in color and 

 are membranous, with scattered pycnidia on the surface. Leaves of 

 both young and mature tomato plants are susceptible to spotting. The 

 spots are brown to almost black, definite in outline, and variable in 

 size. Frequently several spots coalesce, forming irregular blotches. 

 The lower leaves became infected first in the experiments, spots appear- 

 ing upon blade and petiole. Within two weeks after inoculation by 

 spraying, the leaves had become discolored and shriveled and were falling 

 from the stem. Upon the surface of the leaf spots small dark pycnidia 

 occurred singly or in groups. Reisolations in plate culture were made 

 from tissue cut from diseased spots. 



MYCELIAL GROWTH 



The mycelium of this fungus forms a dense network of hyphal threads 

 within the tissues of the host plant. The hyphae are septate, frequently 

 branching, and are hyaline to brown in color. Various stages in the 

 development of pycnidia were observed in the tissue of the host, from 

 the first intertwining of hyphal threads to the formation of a definite 

 fruiting chamber, having dark irregularly shaped outer cells. Numerous 

 oil drops were observ^ed in hypha grown upon artificial media. 



PYCNIDIAL DEVELOPMENT 



The pycnidia are subglobose, membranous to carbonaceous, smooth, 

 slightly papillate with a distinct central pore (occasionally two pores), 

 color varying from almost hyaline to black, according to age and medium. 

 There is considerable variation in size. Pycnidia occur scattered or in 

 groups. They are at first covered by the epidermis, but later break 

 through, the spores issuing in long coils through a central pore. In 

 culture ^e flesh-colored spore exudate frequently forms a slime on the 

 surface of the medium. The pycnidial wall is thin, with brownish outer 

 cells and hyaline inner cells. One-celled pycnospores are developed from 

 the end of the delicate filiform basidia which arise from the inner cells. 



