156 



CHAPTER IX 



Eye Spot. ^^ Cercospora sacchari (Van Breda de Haan). — Hab. in foliis, qua 

 maculantur, sacchari officinarum. Hyphce pluriseptatce , hrunecB, 120-60; conidia 

 60-80x9-12, vermicularia, 5-8 septata, brunea. 



The spores of this fungus, after Cobb, are shown in Fig. 47. The presence 

 of this disease is indicated by small red dots, which grow into long elliptical 

 dark red spots, with a light yellow margin ; at a later stage the centre be- 

 comes a dull dead yellow, surrounded by a dark red area, and this is circum- 

 scribed by a bright yellow border ; 

 the elongated elliptical shape 

 of the spots, which may grow 

 up to 1 1 to 2 inches in length, 

 is retained ; the appearance 



Fig. 46 



X500 6 



of the spots is not dissimilar to the eye on a peacock's wing. With a 

 pocket lens hairs (conidiophores) may be seen growing from the leaf. 



In Java the disease does not appear on Cheribon cane or on cane grown 

 on mountain plantations. In Hawaii it only makes progress in wet weather. 

 Varieties differ much in susceptibihty, and in one Hawaiian seedling, H 333, 

 it appears as a stem disease. This disease is probably the same as Helmin- 

 thosporium sacchari, reported in India by Butler.®^ 



Eye Spot of the Leaf Sheath. '" Cercospora vagina (Kriiger) . — This disease 

 is characterized by a brick-red spot appearing on the leaf sheath ; the red 

 coloration does not spread over the leaf sheath ; the centre of the spot 



Fig. 48 



Fig. 49 



eventually becomes black. In Fig. 48 are shown the spores after Kriiger. 

 Their length is from 19-6 to 40 microns, with an average of 25-2 microns, 

 and with a breadth of 7 microns. The disease has been reported from Java, 

 British Guiana, Porto Rico, Santo Domingo, Cuba, Jamaica, Louisiana and 

 India. 



Black Spot of the Leaf Base. '^ Cercospora acerosum (Dickoff and Hein) . — This 

 disease causes a blackening of the leaf base. The spores, shown in Fig. 49, 



