Genetic aspects of seed harvests for the artificial regeneration of wild service tree (Sorbus torminalis [L.] Crantz)

Isoenzymes were used to study the genetic variation of 121 mature trees of Sorbus torminalis in a natural stand and a subset of 21 high yielding seed trees in the same stand used for a commercial harvest. Eight enzyme systems were studied. The genetic variation of the mature stand was higher than that of other stands reported in the literature. However, this level of genetic variation was not represented to the same extent by the seeds of the commercial harvest. Differences between the bud sample taken from the mature stand and the seed sample taken from the commercial subset were particularly obvious with respect to diversity measures and heterozygosities. The hypothetical gametic multilocus diversity (HGMD) of a bud sample of the mature Sorbus torminalis trees was more than 70% higher (94.1) than the value of the seed harvest sample (55.1). Deviations between the genetic structures of both samples were statistically significant. There is no indication that inbreeding is an essential component of the mating system of Sorbus torminalis. The potential causes for the lack of Sorbus torminalis seedlings and saplings originated from seeds and their consequences for regenerating this species are discussed. This research underscores that sampling a forest tree population for commercial harvest can result in a statistically significant reduction in the genetic diversity of the sampled group relative to the overall population.