XIII, A. 5 Reinking: Philipipne Economic-Plant Diseases 225 



Cercospora nicotianae Ell. et Ev. 

 a, group of conidiophores, two 

 of which are germinating ( X 

 340) ; b, germinating conidia 

 (X 340). 



millimeters in diameter. The center of each spot is ashen gray 

 and is bordered with a brown ring (Plate XII, fig. 3). In the 

 ashen gray portion of older spots is a blackish dust. 



Causal organism. — The black- 

 ish dust is made up of conidio- 

 phores and conidia. The coni- 

 diophores are produced in groups 

 from stomata and are light brown 

 and septate. They may ger- 

 minate under suitable conditions, 

 producing hyaline germ tubes 

 that infect the plant. The coni- 

 dia are typical Cercospora coni- 

 dia. They are hyaline, much 

 elongated, thick at one end, 

 tapering to the other. Spores 

 frequently contain as many as' 

 fifteen cells (fig. 24). Germi- 

 nation usually takes place by the 

 production of from two to four 

 germ tubes from the same 

 number of cells. 



Control. — Badly diseased lower leaves should be collected and 

 burned or used for a low-grade tobacco. Diseased leaves should 

 not be left in the soil. Open planting should be practiced where 

 possible. Crop rotation is effective in checking the disease. 



ROOT GALLS: NEMATODES, HETERODERA RADICICOLA GREEF ET MULLER 



Symptoms. — Root galls are frequently produced by nematodes ; 

 however, no serious damage has been reported. The galls may 

 be formed on the smaller or larger roots and sometimes they 

 are produced in abundance. Plants severely attacked are stunted 

 or may be killed (Plate XII, fig. 4). The nematodes seem to 

 make way for the entrance of the bacteria, causing the tobacco 

 wilt. 



Control. — Rotation of crops will help to keep the organism at 

 a minimum. 



ORYZA SATIVA LINN. RICE 



BACTERIAL LEAF STRIPE 



Symptoms. — A striping of the leaves of certain varieties of 

 upland rice may be serious. In the young stages the stripes 

 are from 0.5 to 1 millimeter wide and from 3 to 5 millimeters 

 long, run lengthwise, and have a watery, dark green, translu- 

 cent appearance. In this stage the disease is usually confined 



