CHAPTER XXIV 



DISEASES OF CORN AND SORGHUMS 



Corn. 



Brown Rust. 

 The most widely distributed leaf-rust of maize is caused by the 

 fungus Puccinia Sorghi, which in spite of its name does not 

 attack sorghum. It causes comparatively little discoloration 

 of the leaf, but the brown pustules in which the spores are 

 developed are more or less conspicuous, according to the degree 

 of infestation. 



Leaves heavily infested with this fungus were received from 

 Montserrat in February 1915, accompanied by a report that it 

 was very prevalent on a large field planted some ten weeks 

 previously, and had been common from the time the plants 

 flowered. It has since been reported from St. Vincent, St. Lucia 

 and Antigua. 



In the United States this rust is not regarded as having much 

 economic importance. Usually it becomes common too late in 

 the season to do much damage. When favoured by exceptional 

 climatic conditions it may appear earlier and have a considerable 

 influence on the yield. In South Africa serious outbreaks are 

 reported as having occurred in certain districts. 



Causative Fungus. 



Puccinia Sorghi, Schw. (P. Maydis Bereng.) 

 (i) Aecial stage {Aecidium oxalidis) on Oxalis spp. Peridia 

 usually on the under side of the leaves, crowded, concentric ; 

 epispore smooth, 24-28 micr. 



(2) Uredinial stage, on maize. Sori on both sides of the leaf, 

 numerous, often confluent ; spores brown, globose to ovate, 

 23-30x22-26 micr., slightly verrucose. 



(3) Teliospores black, ovate-oblong or clavate-obtuse, con- 

 stricted ; epispore thick ; 28-45 x 12-17 micr. ; smooth ; 

 pedicel long ; 5 micr., persistent. 



Red Rust. 

 The fungus Puccinia purpurea Cke. (see p. 261), which is very 

 common on sorghums in these islands, is reported to attack 

 maize in Natal. It may be distinguished on that plant by the 

 deep purplish-red discoloration produced on the leaves, like that 

 familiar on sorghum. 



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