Female Fertility and Mating Type Distribution in a South African Population of Fusarium subglutinans f. sp. pini

Fusarium subglutinans f. sp. pini is the causal agent of pitch canker disease of pines. The initial occurrence of F. subglutinans f. sp. pini in South Africa was limited to a single nursery, and isolates from this population are capable of reproducing sexually. We determined the effective population number, N(e), of this population by using mating type and male/hermaphrodite polymorphisms as indicators. The effective population number for mating type, N(e(mt)), is 99% of the count (total population), and that for male/hermaphrodite status, N(e(f)), is 42 to 46% of the count (total population). The number of strains that can function as the female parent limits the effective population number of this population. If this population is stable, then, depending upon assumptions about mutation and selection, sexual reproduction need occur only once per 26 to 153 asexual generations to maintain this level of sexual fertility.