Genetic diversity of Sandalwood in Imogiri, Gunung Sewu

Sandalwood population decreased rapidly in nature, thus strengthen the need of reintroduction
to preserve its population diversity. The re-introduction materials were taken from
Gunung Sewu area, which consisted of several sandalwood landraces varied in population
structures and genetic diversity. One of those landraces, which is also considered the oldest
based on the herbarium investigation, was Imogiri landrace in which the oldest sandalwood
specimens were dated on 1853. This research applied isoenzyme analysis to estimate genetic
structure of sandalwood in several sandalwood stand differed by landscapes in Imogiri. The
isoenzyme samples, a juvenile leaf, were taken with 100% IS (census method), along its natural
distribution in five areas: (1) Kawasan Hutan Wisata Mangunan, (2) Bukit Panguk-Kediwung,
(3) Telaga Giri, (4) Bukit Mojo Gumelem and (5) Karangtengah Village. The first to third areas
are formed in cliff landscapes which are lead to Oya River. The fourth and fifth areas are
located in the local private yard and are arranged in an agroforestry pattern. The fifth area,
which is located near the Makam Raja-Raja Mataram, is also considered as the oldest
sandalwood stand in Imogiri. A 224 samples collected consisted of 136 parent trees and 88
seedlings. There were 22 trees found bearing flowers, and as well as the seedlings, mostly were
found in the private yard. Only one seedling was found in the cliff landscapes. Spatially, the
highest genetic diversity (He 0.512; Ho 0.672; Fis -0.313) was found on the Karangtengah
Village which is considered as the oldest sandalwood stands in Imogiri. Genetic diversity on
other stands are varied (He 0.436 to 0.471; Ho 0.462 to 0.603; Fis -0.382 to 0.020).
Temporally, genetic diversity is higher on the older phase (parents: : He 0.483; Ho 0.539; Fis -
0.117) in compared to the younger generation (seedlings: He 0.407; Ho 0.419; Fis -0.030).
Mating system is outcrossing which is indicated by the negative fixation index. Imogiri
landrace showed the highest heterozygosity among others in Gunung Sewu and Eastern Islands
of Indonesia, however it also had rare alleles that indicated the existence of genetic drift and
bottleneck effect. The heterozygosity reduction at the seedling level might be attributed to the
poor natural regeneration of sandalwood in Imogiri, which might occurred due to the
unsynchronized flowering, low effective population size or lack of flowering trees (such as a
case in Giri stand), the absence of seedbeds (a case in most of landrace grown in the verge of
cliffs), and/or the absence of host (a case in Karangtengah Village). Seedlings were only found
on a place where agroforestry pattern applied; implied that human interference is needed to
preserve sandalwood from extinction. In order to enhance cross-mating system and prevent the
increase of homozygosity, the genetic infusions with more diverse genotypes is recommended.