72. PLANT DISEASES 



COLOCASIA DISEASE 



{Perofiospora trickotoma, Massee.) 



Colocasia esculenta, Schott, an important food-plant in 

 the West Indies, is known by one or other of the follow- 

 ing names in the different islands: 'Cocoes,' 'Tayas,' 

 'Tanias,' ' Tanniers,' 'Eddoes.' 



In the early stage of the disease a ' tuber ' presents a 

 number of yellow dots when cut across, which correspond 

 in position to the vascular bundles ; these become darker 

 in colour, and finally the entire substance, except a thin 

 peripheral portion, becomes blackish and decayed, but 

 remains fairly dry. The conidial stage of the fungus 

 appears on the surface, and oospores are numerous in the 

 decayed tissue. The disease attacks the roots after they 

 are lifted. 



Preventive Means. — The roots should be thoroughly 

 dried, and only sound ones used for propagation. Soil 

 that has produced a diseased crop should not be used again 

 for colocasias for two or three years. 



Morris and Massee, Journ. Linn. Soc, 1887, p. 45, figs. 



Peronospora t?-ifolioruni, De Bary. — This species attacks 

 numerous plants belonging to the Leguminosae, cultivated 

 and wild ; Trifolium, Lnpitiiis^ Aledicago, Lotus, Coronilla, 

 Meiilotiis, Ono?iis, etc. 



The leaves become covered with a pinkish-grey down, 

 due to the numerous conidiophores. The conidia are 

 broadly elliptical, greyish-lilac. Oospores smooth, reddish 

 brown. When clover or lucerne is attacked, the leaves 

 turn yellow and fall, and the only remedy against a repeti- 



