210 The Philippine Journal of Science lais 



cankee: phytophthora faberi maublanc 



Symptoms. — The canker of Para rubber may be rather hard 

 to detect in its early stages. In the Phihppines the disease 

 is similar to that discussed by Fetch in Ceylon. External symp- 

 toms usually consist in a darkening of the bark, and in older 

 cases there may be a definite demarcation of the diseased area. 

 Most frequently the diseased area is smooth, but it may be 

 cracked and scaly. During damp weather a reddish or purplish 

 liquid sometimes exudes from the larger diseased areas. On 

 older trees the disease cannot always be noticed from outward 

 appearances, for a true cankered condition may not be produced. 

 Internal symptoms are then the only indications of disease. Dis- 

 eased trees cease to yield latex. The cortex, instead of its 

 healthy white, yellowish, or clear red appearance, is characterized 

 by a black layer produced under the outer brown bark and 

 underneath this the cortex is discolored, in young cases gray, 

 and in older cases a purplish red. In young cases only the 

 outer layer of the bark may be diseased. This can be detected 

 by carefully scraping the areas that do not produce latex to 

 determine whether the cortex is blackish instead of being a 

 healthy color. 



When diseased trees have been cut down and piled ready for 

 burning, they may be attacked by Megalonectria pseudotrichia 

 (Schw.) Speg., which is characterized by a dense reddish mass 

 of raised bodies, the perithecia, produced on the surface of the 

 trees. This fungus is regarded as a saprophyte and is only 

 found on the dead or weakened portions of trees. It may, how- 

 ever, gain entrance into diseased areas of living trees, conse- 

 quently it should be guarded against. 



Catisal organism. — The Para rubber canker is produced by the 

 same fungus that produces the black rot of Hevea fruits and 

 also the black rot of pods and canker of cacao. The organism 

 is more fully discussed under cacao. On rubber, so far as has 

 been observed, only the conidial or sporangial stage is produced. 

 Generally the asexual spore bodies are roundish or egg-shaped. 

 Conidia germinate directly by the production of a germ tube 

 that develops into the mycelium. These same spores under 

 favorable damp or rainy conditions may germinate by the produc- 

 tion of zoospores. The spore body is then called a sporangium 

 or a zoosporangium. The zoospores swim about for a time, 

 then come to rest and germinate as ordinary conidia by the 

 production of a germ tube, which penetrates into the host pri- 

 marily through injuries. The mycelium is almost always in- 

 ternal, spreading through the bark and is seldom found growing 



