PHYSIOLOGIC RACES OF BUNT OF WHEAT

Abstract

The discovery of physiologic races in covered smut of barley (2, 4) and in the loose and covered smuts of oats (6, 8) has greatly stimulated the study of host specialization in the other cereal smuts. From this standpoint, these parasites have previously been a neglected group, although physiologic specialization has long been known to be of wide occurrence among the parasitic fungi (5). This neglect is due, in part at least, to the fact that most collections of smut spores are capable of infecting a wide range of hosts, and thus relatively few varieties are of value in differentiating specialized races. Another factor in the situation is due to the peculiar mode of infection of the smuts. In most of them entrance of the fungus occurs through the young seedling by means of germinating smut spores present on the seed or in the adjacent soil. Various environal conditions such as soil temperature, soil moisture, etc., play a very large part in determining whether infection will occur and, unless the proper combination of conditions is present, very low percentages of infection take place and quite variable results are obtained with equally susceptible varieties. Faris (3), in his studies on the influence of various factors on the infection of wheat by Tilletia laevis Kuhn and T. tritici (Bjerk) Winter, obtained some evidence of a difference in the infection capacity of collections of bunt from different localities. In his experiments he used six collections of each smut, testing them on ten different varieties of winter wheat. The most definite evidence of specialization was observed in the reaction of the variety Kanred to certain collections of T. tritici. The writer has for several years studied the behavior of wheat varieties to both species of bunt (Tillelia laevis and T. tritici) although very little of the accumulated data has been published (7). However, collections of both species have been obtained from widely separated localities and tried out on many varieties of wheat. For the most part, winter varieties have been grown, and by far the larger number of those tested have been more or less severely infected by practically all the collections of bunt. A few varieties have, however, shown marked differences in their behavior to some of the bunt collections, and thus furnish striking evidence of the existence of physiologic races in both the species of Tilletia. A brief