224 



The Philippine Journal of Science 



DAMPING OFF OF SEEDLINGS: RHIZOCTONIA, PYTHIUM DBffiARYANUM HESSE, 

 PHYTOPHTHORA NICOTIANAE BREDA DE HAAN 



Symptoms. — Tobacco seedlings are extremely susceptible to 

 damping off. All the plants in a given flat may be damped off. 

 The young tender plants are attacked just at the surface of the 

 ground. The stem shrinks and becomes rather watery, and the 

 seedlings fall over (Plate XIII, figs. 2 and 3). 



Causal organism. — A study of 

 the fungi causing this condition 

 revealed the presence of a Rhi- 

 zoctonia, usually associated with 

 Pythium debaryanum Hesse. 

 Phytophthora nicotianae Breda 

 de Haan has been also proved to 

 cause damping off of tobacco 

 (fig. 23). 



Control. — All soil used for the 

 growth of seedlings should be 

 thoroughly sterilized by heating. 

 The seedlings should be grown 

 in well-aerated places, free from 

 excessive moisture, and should 

 be placed in the sun from time 

 to time. 



Damping off is very general 

 and severe with flower and vege- 

 table seedlings. In the major- 

 ity of cases a Rhizoctonia was 

 found, and the latter was usually 

 associated with a fungus sim- 

 ilar to Pythium debaryanum 

 Hesse. A Sclerotium was also 

 found to cause a damping off or 

 stem rot of coffee seedlings 

 and other plants. Phytophthora nicotianae Breda de Haan and 

 a Fu^arium also have been determined to cause damping off. 

 These troubles can be easily avoided by soil sterilization. 



LEAF SPOT: CERCOSPORA NICOTIANAE ELLIS ET EVERHART 



Symptoms. — The common "frog eye" of tobacco is found 

 generally in tobacco-growing regions. Serious and extensive 

 damage may be done to the lower leaves, especially where the 

 plants are crowded. The disease is characterized by the pro- 

 duction of irregularly circular spots, which are from 1 to 5 



phytophthora nicotianae Breda de 

 Haan. Section of damped-oflf 

 stem of tobacco, showing myce- 

 lium penetrating throughout the 

 tissue (X 310). 



