262 DISEASES OF QROP-PLANTS 



The spores are very resistant, and the occurrence of a small 

 quantity of sniutted material among the seed corn is capable 

 of producing widespread infection in the following crop. The 

 disease is thus cumulative, and its occurrence even in small 

 proportions should therefore not be considered negligible. 



Causative Fungus. 



Sphacelotheca (Ustilago) Sorghi (Lk.) CI. Spores single, sub- 

 spherical to spherical, smooth, contents often granular, 5.5-8.5 

 micr. diameter ; covered at first by a membrane of fungus origin. 

 On various Andropogon (Sorghum) species, including Johnson 

 grass. 



Control. 



Treatment is rendered easy by the absence of the fungus from 

 the interior of the seed, and owing to the fact that only very 

 young plants can be infected. Any method which secures the 

 sterilisation of the seed without destroying its germinative power 

 is effective. Steeping the seed in copper sulphate solution, 

 according to the instructions on page loi is the simplest remedy ; 

 the formalin treatment is also applicable. 



Head Smut. 



The head smut differs from the preceding disease in that 

 instead of the grains being affected separately, the whole head 

 or, rarely, a section of it is conglomerated into a smutted miss. 

 The same fungus occurs on corn. It has a wide distribution 

 where sorghums are grown, including North America, but is not 

 common in that country. It has not been noticed in these 

 islands. The disease is not amenable to seed treatment, as, 

 although the infestation is systemic and seedlings are commonly 

 infected, this appears to arise from material originating from 

 wind-blown spores in the soil. 



The variety known as milo is immune to this as to other 

 smuts, and kaffir and broom corn are resistant to it. 



Causative fungus. 



Sorosporium reilianum McAlp. {Ustilago reiliana Kiihn, 

 sphacelotheca reiliana Clint) Spores loosely aggregated into 

 groups, minutely roughened, 9-14 micr. 



