CHAPTER V 
DISEASES DUE TO FUNGI (Continued) 
3. Stem, Leaf, and Fruit Diseases 
(a) STEM DISEASES 
Sclerotinia Stem Rot.—While this disease appears regu- 
larly every year, it ranks as one of the least important of 
the diseases of glasshouse plants. Sclerotinia sclerotiorum 
Massee (30) is the cause of the disease, and attacks a 
wide range of host plants, including beans, cabbages, 
carrots, chrysanthemums, cucumbers, melons, petunias, 
potatoes, sweet-peas, turnips, and zinnias. Plants are 
generally attacked at the soil level, where a white mould 
develops on the stem and also spreads into the soil. 
The fungal hyphe grow rapidly into the plant, choking 
up the conducting vessels and disorganizing the softer 
tissues. The pith is destroyed and a hollow cavity pro- 
duced. Rotting of the stem progresses steadily up the 
plant until some six inches may be involved. Diseased 
plants show all the common symptoms of wilt, and soon 
die. Following the decay of the stem, small, soft, white 
bodies may be found embedded in the white mould. 
These vary in size from a sixteenth of an inch to a quarter 
of an inch in diameter, and eventually dry, becoming 
hard and black (Fig. 19). Such bodies, which are the 
sclerotia or resting forms of the fungus, are found within 
the hollow stem as well as on the outside. Tomato and 
cucumber stems are frequently attacked high up from 
the ground, especially on the angles between the leaves 
and the stem, which hold moisture, and so provide 
88 
