Pyrus (tribe Maleae), which includes economically important fruit
trees, is widely distributed in Asia, Europe, and North Africa. Three primary species
(P. ussuriensis, P. calleryana,
and P. pyrifolia) and
numerous infraspecific taxa occur in Korea. Of several infraspecific taxa, P. ussuriensis var. hakunensis occurs exclusively in Mt. Baekun-san with the diagnostic
feature of densely brown haired twigs and petioles. Previsous studies provided
limited knowledge toward our understanding of overall species relationships and
evaluation of infraspecific taxa. We newly developed and utilized 12 SSR markers
to estimate genetic diversity and assess relationship among wild and cultivated
accessions of P. ussuriensis.
A total of 52 individuals (37 wild form Baekun-san and 15 cultivated, known as
“Baekun Pear”, from Gwangyang) of P. ussuriensis var. hakunensis and
85 individuals of P. ussuriensis were collected from Korea, China, and
Russia. The genetic diversity of P. ussuriensis var. hakunensis
was substainly higher, with numerous private alleles, than that of its close
relative P. ussuriensis, and
overall Korean populations of P. ussuriensis exhibited higher
diversity than the populations from neighboring countries. The AMOVA suggested that 70% of
variance was found within populations, while the rest (30%) was among
populations. The cultivated accessions of P. ussuriensis var. hakunensis
from Gwangyang is closely related to P. ussuriensis population in Gurye,
questioning its origin. The STRUCTURE analysis identified three genetic groups:
(1) P. ussuriensis from Korea, China,
and Russia, (2) wild population of P.
ussuriensis var. hakunensis, and
(3) P. ussuriensis in Gurye and cultivated
accessions of P. ussuriensis var. hakunensis. Limited gene flow appears to
be a driving factor for differentiation of P. ussuriensis var.
hakunensis. P. ussuriensis var. hakunensis as a distinct
taxon based on subtle diagnostic feature and geographic distribution seems
questionable. However, the current study showed that P. ussuriensis var.
hakunensis harbor unique gene pool, possibly diverged significantly from
the remaining populations of P.
ussuriensis. Therefore, further study using NGS-based technologies (e.g.,
GBS, MIG-Seq, etc) will shed light on taxonomic status and evaluation of
numerous infraspecific taxa of P.
ussuriensis and related taxa.