Covered Smut of Barley. 109 



CHAPTER XVII. 



Covered Smut of Barley. 



(Ustilaqo hordei (Pers.) Kell. and Sw.) 



This smut is not so readily observed as the Naked smut, and therefore it 

 is sometimes said to be not so common, but as to relative prevalence it is 

 found to be the more common of the two. At Dookie, where a number of 

 varieties of barley are grown, it is much more general than the Naked smut, 

 and it is a very marked feature of the skinless barleys. This wider distri- 

 bution may ba due to the compactness of this smut, which gives it exactly 

 the same chance as Stinking smut of wheat, which is distributed in a whole- 

 sale manner in the form of smut-balls, and also to the fact that the floral 

 infection necessary in the Naked smut will be more uncertain (Plate XL). 



The two species of smut found on cultivated barley {U. hordei and U. 

 nuda) have only comparatively recently been separated, and they were 

 formerly included under U. segetum. The differences between the two are 

 very marked, independent of what is indicated by the common name. In 

 the Naked smut the diseased ears are ultimately free from the leaf-sheath 

 and fully exposed, while in the Covered smut the ears are more or less en- 

 closed. The spores in the former are echinulate and powdery, and scattered 

 by the wind at the flowering period, while in the latter they are smooth, 

 slightly larger and compact in the mass, and remain intact till later harvest. 

 In the Naked smut the spores in the mass have a decided greenish tinge, 

 which is absent from the Covered smut. The germination, too, is very dis- 

 tinct. In the Naked smut only a germinal tube is formed, which elongates 

 and branches and becomes a regular septate mycelium, but in the Covered 

 smut conidia are produced. Lastly, the Naked smut has been proved to 

 infect the flower and not the seedling and the Covered smut infects the 

 seedling, as indicated by the certain treatment of the seed with bluestone 

 solution. The differences between the two may be briefly summarized : — 



Covered Smut. Naked Smut. 



Ears — More or less enclosed in leaf- Free from leaf-sheath. 



sheath 

 Spores — Compact in mass, with Powdery, echinulate, and scattert(i 



greenish tinge, smooth, and re- during flowering time. 



maining intact till after harvest 

 Germination — Conidia produced . . No conidia. 

 Infection — Seedling . . . . Flower. 



Germination, 

 The germination of the spores has been described by Kellerman and 

 Swingle,'^ Brefeld* and Herzberg. Affected barley was obtained from the 

 neighbourhood of Melbourne in November, 1906, and the spores germinated 

 freely in water in December. Also from Port Fairy in January, 11)07, and 

 when tested in June the spores readily germinated. The promycelium was 

 generally .'5-septate, only one being formed from each spore, according to 

 Herzberg, but I have found occasionally more than one. Promycelial spores 

 were produced both laterally and terminally, and were generally attached by a 

 slender sterigma. sometimes two being given off together, each with their 

 own sterigma. The promycelium was sometimes branched, the l)ranches 

 becoming septate and giving off conidia, and knee-joints were very common, 



