PHYSIOLOGIC FORMS OF LOOSE SMUT OF WHEAT

Abstract

Four physiologic forms of loose smut of wheat have been found in Manitoba. Two of these forms were collected in the field, one on Reward and the other on Mindum. The two other forms appeared in the course of artificial inoculations in the greenhouse. The origin of physiologic forms of loose smut of wheat is discussed. It is considered that one of the forms that appeared in the course of the greenhouse inoculations may have resulted from a mutation. Evidence is put forward which indicates that different physiologic forms occur in Eastern and Western Canada. None of the 13 varieties of wheat used in the inoculation experiments proved to be resistant to all physiologic forms. The inoculation of Reward, Marquis, Garnet, and Pentad × Marquis with their own spores for four generations did not result in appreciably increasing the infections on these varieties. It was also shown that the healthy Reward plants that are sometimes present in a population grown from artificially inoculated seed are not resistant to loose smut, but have escaped infection because of faulty inoculation.