86 Loose Smiif of Wheat. 



CHAPTER XIII. 



Loose Smut of Wheat. 

 {Ustilago tritici (Pers.) Jens.) 



Of the three different species of smut known on the wheat plant in 

 Austraha this is one considered the least injurious, but it may be present to 

 a considerable extent and yet overlooked, because the stalks affected 

 are usually stunted. Like the oat smut it is produced in the ovaries, and 

 destroys the various parts of the flower, so much so that at harvest time 

 only the bare stalks of the ears remain after the spores have been blown 

 away. It is distinguished as loose smut from the powdery nature of the 

 spores, or flying smut, from the way in which it flies when blown, and the 

 ears are often spoken of as " snuffy ears" by the farmer (Plates III., VI.). 

 It differs from the much more common stinking smut or bunt in having no 

 objectionable odour, and the loose dusty mass of spores ripen and are blown 

 away while the wheat plant is in flower, instead of remaining and falling 

 what would otherwise be the grain with an evil-smelling compact mass of 

 spores, only broken up and scattered when being harvested or threshed. 



When a stool is affected with loose smut, the stalks are generally of a 

 purplish tint, so that they can be readily picked out from among the general 

 crop. The same has been observed in the naked smut of barley, but it is not 

 particularly so in the case of loose smut of oats. This purpUsh colour is 

 natural to some wheats, such as Purple Straws, but it occurs in other varieties 

 as well when smutted. It is sometimes attributed to premature ripening, 

 the food materials in the straw not being completely converted into food for 

 the embryo. But I am incUned to think, as it occurs particularly in those 

 cases where flower infection takes place, that the young embryo is influenced 

 in some way by the fungus filaments present in the grain, and this is after- 

 wards shown in the peculiar colour of the straw. 



Unlike the loose smut of oats, it is not uncommon to find stools with 

 both smutted and sound ears. 



Germination. 



Kellerman and Swingle"^ and Herzberg^ have described the germination 

 ■of this species, and I have found it to germinate readily in water and in a 

 nutritive solution. After being kept for five months the spores germinated 

 at once. In water they germinated fairly well in 21 hours, and in three 

 days there were copious branchings. The main germ-tube was nearly always 

 slightly curved, although it might grow out quite straight. The numerous 

 branches might arise either beneath a septum or opposite to each other, 

 or sometimes a protuberance opposite to a septum grew out into two 

 branches alongside of each other, above and below the septum. 



In a nutritive solution such as hay infusion, after eighteen hours a slender 

 germ-tube was formed, and it is generally characteristic of it that it curves 

 in a sickle-shaped fashion. After 24 hours branches are freely formed, 

 and the whole grows out into a much-branched mycelium without the 

 formation of any conidia. This pecuUar curvature of the branches is so 

 striking that when copious branching has taken place the whole resembles 

 a loosely wound coil of filaments. 



