Genetic diversity of Sandalwood in Imogiri, Gunung Sewu

Abstract

Sandalwood population decreased rapidly in nature, thus strengthen the need of re-introduction 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. The natural regeneration by sexual reproduction should be supported by flowering stimulation, pollination management, providing seedbeds, and planting more primary and secondary hosts.