Abstract
Mycelia of Gremmeniella abietina isolated from the same ascus were paired in seedlings of Pinus sylvestris and the production of apothecia determined. G. abietina was found to be a heterothallic fungus in which mating is controlled by a single locus composed of at least two mating allcles. Independent of climatic conditions isolates of type B produced greater number of apothecia than those of type A.