DISEASES OF CORN AND SORGHUMS 261 



reported to be common on maize in Porto Rico, hastening the 

 death of old or basal leaves. It has no economic importance. 



Sorghums. 



Rust. 



The most conspicuous rust disease in these islands is that 

 caused on the cultivated sorghums by Puccinia purpurea. Cke. 

 It appears to be general on Guinea corn, imphee, Sudan grass, 

 and Johnson grass. It also occurs in the southern United States, 

 in Cuba, Jamaica, Porto Rico and Bermuda. 



Appearance of the Disease. 



Elongated purplish-red blotches are produced on the leaves, 

 and in these the sori are developed. In severe infestations the 

 leaves are in this way very much discoloured, and there would 

 seem to be no question that the growth of the plant is con- 

 siderably affected. The crop is nowhere in these islands of any 

 great importance, and the disease receives no attention. 



Causative fungus. 



Puccinia purpurea Cke. [Uredo Sorghi, Fckl. not P. Sorghi 

 Schw.) Urediniospores ovate, 35x25-30 micr. smooth, brown. 

 Teliospores elongate ovate, brown, long-pedicellate, 40-45 x 22-25 

 micr. Occurs also on maize, which see. 



Control. 



Would be best attempted by selection of resistant types. 



Kernel Smut. 



The common sorghum smut, Sphacelotheca Sorghi, occurs from 

 time to time on imphee and Guinea corn in the West Indies. It 

 is of general occurrence about the world, and occasionally is 

 severe in its effects. In these islands, where the crop is more 

 usually grown as fodder than for grain, the disease has not 

 attracted much attention. 



The spores of the fungus are usually sown with the seed, 

 germinate in the soil at the same time, and infect the seedlings 

 at an early stage. The mycelium of the fungus keeps pace with 

 the extension of the plant in the form of thin threads which grow 

 up through the softer tissues, especially the pith. No particular 

 damage to the plant is caused and no sign of the disease is visible 

 until the period of flowering, when the fungus develops rapidly 

 in the anthers and ovaries, and there produces masses of black 

 powdery spores which replace the pollen and the seeds. The 

 outward appearance of the panicles is not much altered until the 

 membrane which at first encloses the spore masses bursts, when 

 they appear as if coated with powdery soot. 



