xni. A, 5 Reinking: Philippine Economic-Plant Diseases 223 



15 centimeters to 1 meter in height are visibly affected. Wilting 

 is the first indication of disease ; later a brown stripe is produced, 

 usually from the petioles and extending down the stem. A slight 

 shrinkage in the brown-striped portion may take place. Dis- 

 eased plants die (Plate XII, fig. 2). 



No serious epidemics in tobacco plantations have been re- 

 ported ; however, they may occur at any time, unless the organ- 

 ism be kept in check. 



Causal organism. — The organism is the same as that causing 

 wilts of all solanaceous plants. The bacteria gain entrance into 

 the plant chiefly through mechanical and insect injuries. Nema- 

 tode root galls are frequently found on wilted plants. The bac- 

 teria clog up the xylem tubes, stopping the flow of water and 

 causing the wilt. In later stages of infection the parenchyma 

 may be invaded. 



Control. — It is practically impossible to control the disease in 

 heavily infected soil. The organism should be kept out of new 

 soil by planting only healthy plants produced from seeds of 

 healthy plants. Soil should be sterilized when used for seedlings 

 grown in flats. During transplanting care should be taken to 

 avoid injury of the roots of young plants. Insect enemies and 

 nematodes should be held in check. All diseased plants should 

 be burned. If the soil be heavily infected with bacteria, a five- 

 year system of crop rotation, in which no tomatoes, potatoes, 

 eggplants, pepper, or other solanaceous plants are grown, should 

 be practiced. The production of disease-resisting or enduring 

 plants would hold the disease in check. 



CHLOROSIS 



Symptoms. — A chlorotic condition or yellowing of plants is 

 frequently found, but this is not considered a serious affection. 



CURING AND FERMENTING TROUBLES: LEAF SPOTTING 



Symptoms. — During fermenting of the leaves, leaf spotting 

 frequently takes place. The spots are greenish and circular, 

 from 3 to 15 millimeters in diameter. Infected leaves cannot 

 be used as wrapper. 



Causal organism,. — Isolation experiments indicate that this 

 disease is due to a fungus. As yet no spores have been observed. 

 Mycelium is produced in abundance in the spots. The fungus 

 grows well in pure culture, producing a thick dark gray growth. 



Control. — Infected leaves should be sorted out, so as to keep 

 the disease from spreading. 



