180 



The Philippine Journal of Science 



The bacteria gain entrance into the plant through water pores 

 at the margin of the leaf and through injuries on the leaf sur- 

 face. After gaining entrance, the organism multiplies rapidly 

 and spreads primarily through the fibrovascular bundles, causing 

 them to blacken. The bacteria frequently ooze in a yellow mass 

 from the cut bundles. From the leaves the organism spreads 

 through the vascular bundles into the stem, causing a rot and 

 consequent death of the plant (Plate X, fig. 2). 



Control. — The collection and destruction of infected leaves may 

 be effective as a control, if these leaves be picked before the 

 organism has spread into the stem of the plant. When once 

 the soil has become infected, crop rotation is the only method 

 of control. Care should be taken that only healthy, noninfected 

 seedlings are set out from the seed bed. The disease is spread 

 on seeds. Seed treatment with either mercuric bichloride, 1 to 

 1,000, for fifteen minutes or 1 to 2 per cent formalin for twenty 

 minutes is effective. 



BRASSICA PEKINENSIS (LOUR.) SKEELS. PECHAY 



LEAF spot: CERCOSPORA BRASSICICOLA P. HENNINGS 



Symptoms. — Frequently severe spotting of the lower leaves 

 occurs, making them unfit for food. Characteristic Cercospora 

 spots, with ashen-gray centers bordered with light brown, are 

 produced. These spots range from 1 to 15 millimeters in dia- 

 meter. The older, larger spots frequently have concentric rings 

 of gray and dark brown. The ashen-gray center of older spots 



is covered with a black mass of 

 conidiophores and conidia (Plate 

 II, figs. 1 and 2). 



Causal organism. — The coni- 

 diophores are produced in groups 

 arising from the stomata. They 

 are septate and light brown. 

 The conidia are hyaline, taper- 

 ing, and from five- to fifteen- 

 celled (fig. 7). Conidiophores 

 as well as conidia may germinate 

 and cause infection. 



Control. — All diseased leaves 

 should be collected and burned. 

 Crop rotation should be prac- 



Cercospora brassicicola Henn. a, 



group of conidiophores (X 340) ; LlCeu. 



b. small conidia germinating Ccrcospora armoraciac Sacc. 



(X 340) ; c, typical necdlelike , i i /• j r» • 



conidia (X 340). ^^^so has been found on Brassica 



