CHARACTERISTICS OF STRAINS OF SEPTORIA-NODORUM ADAPTED TO WHEAT OR TO BARLEY

Sixty-four strains of Septoria which had been isolated from a range of hosts at different locations and in different years were characterized for their adaptation to wheat or barley, growth at near-maximum temperature, fluorescence, colony morphology, conidial (pycnidiospore) length and hexokinase and alkaline phosphatase isozymes. For each character except conidial length, the strains could be divided into two or three discrete groups. The variation in these six characters was strongly associated, such that 60 strains could be classified into two groups, designated W-type and B-type. W-type strains are adapted to wheat, produce large colonies at 31-degrees-C, fluoresce, produce brown-pigmented colonies, and have fast isozymes. B-type strains are adapted to barley, produce small colonies at 31-degrees-C, do not fluoresce, produce pink-pigmented colonies, and have slow isozymes. A few strains differed from these norms in one of the six characters, but only one showed an atypical host adaptation. The four unclassified strains differed from W- or B-type in two or more characters. The many differences between the W- and B-types suggest they are genetically distinct populations within Septoria nodorum.