KERAGAMAN GENETIK MERBAU (Intsia bijuga O.Ktze) DAN IMPLIKASINYA BAGI PROGRAM PEMULIAAN

MAHFUDZ,MP, Prof. Dr. Mohammad Na'iem, M.Agr.

2011 | Disertasi | S3 Ilmu Kehutanan

Pemuliaan pohon mempunyai peran strategis sebagai landasan dasar dalam pembangunan hutan tanaman merbau. Keberhasilan program pemuliaan antara lain ditentukan oleh keragaman genetik pada populasi sumber daya genetik yang informasinya belum lengkap. Penelitian dilakukan untuk menaksir tingkat keragaman gentik merbau , baik keragaman antar dan di dalam populasi, menaksir tingkat perkawinan antar kerabat jauh (outcrossing) merbau, menaksir nilai parameter genetik pada pertumbuhan tanaman merbau di lapangan, dan menjelaskan hubungan antara keragaman genetik pada level isoenzim dan pertumbuhan Penelitian dibagi menjadi empat tahap penelitian yaitu : 1) Analisis keragaman struktur populasi merbau, 2) Analisis sistem perkawinan merbau, 3) Pertumbuhan dan parameter genetik merbau, dan 4) Hubungan antara keragaman isoenzim dan pertumbuhan merbau. Penelitian pertama, kedua dan keempat dilakukan di Laboratorium Pemuliaan Fakultas Kehutanan Universitas Gadjah Mada selama dua bulan mulai 18 januari sampai 10 Maret 2010. Penelitian ketiga dilakukan pada dua lokasi uji keturunan yaitu di Kawasan Hutan Penelitian Dengan Tujuan Khusus (KHDTK) Sobang Propinsi Banten dan lokasi kedua di Bintuni Propinsi Papua Barat selama 22 bulan mulai mulai Februari 2008 sampai Desember 2009 . Hasil penelitian menunjukkan rata-rata persentase lokus polimorfik sebesar 96,40% dan rata-rata keragaman genetik (He) sebesar 0,402. Total keragaman genetik merbau masih cukup besar yaitu 0,438. Sebagian besar keragaman genetik yaitu 93,38% didistribusikan dalam populasi dan sisanya sebesar 6,62% didistribusikan antar populasi. Hubungan kekerabatan antara populasi terbagi menjadi 4 kelompok utama. Masih tingginya keragaman genetik merbau antara lain disebabkan oleh adanya perkawinan silang pada merbau yang oleh nilai rerata perkawinan silang pada multi lokus (tm) dan rerata perkawinan silang pada suatu lokus (ts) yang sangat tinggi yaitu tm = 1,00 dan ts = 0,994. Nilai perkawinan kerabat pada merbau sangat rendah yaitu 0,006. Keragaman genetik pada populasi alam merbau yang tinggi sangat mendukung adaptabilitas dan pertumbuhan tanaman merbau di lapangan. Persentase hidup rata-rata tanaman masing-masing mencapai 91,64% dan 98,37% untuk Sobang dan Bintuni. Nilai taksiran heritabilitas baik individu maupun famili pada uji keturunan di Sobang, Bintuni maupun kombinasi keduanya berada pada kisaran sedang dan tinggi untuk ketiga parameter yaitu tinggi, diameter dan percabangan. Kisar an nilai heritabilitas dari sedang dan tinggi nantinya dapat dijadikan informasi awal sebagai dasar dalam melakukan seleksi tanaman pada masa datang. Perhitungan korelasi genetik antara tinggi dan diameter pada penelitian ini tergolong kuat untuk uji keturunan di Sobang (rg =0,96) maupun Bintuni (rg=0,92) serta kombinasi 2 lokasi (rg=0,95). Berdasarkan asal populasinya terdapat informasi awal korelasi yang positif antara keragaman isoenzim dan pertumbuhan tanaman untuk sifat tinggi, diameter dan percabangan yaitu 0,12; 0,10 dan 0,20.

Tree improvement program plays important role in the plantation forest development of merbau.The success of tree improvement program among others, is determined by the genetic variation in resource population known as the basic population and information abaut genetic information is lacking. The research was conducted with objective to: (1) estimate the genetic diversity level of merbau, the genetic diversity within- and between populations, (2) estimate the rates of outcrossing in merbau, (3) estimate the genetic parameters assumed in plant growth in the field, and (4) determine the relationship between genetic diversity on isozyme level and growth. The research was divided into four stages involving: 1) the isozyme genetic diversity analysis and population s structure of merbau, 2) analysis on merbau mating system , 3) growth and genetic parameter of merbau, and 4) the relationship on isozyme genetic diversity and growth. The first, second, and fourth researches were conducted in the Laboratory of Plant Breeding, at the Faculty of Forestry, Gadjah Mada University for two months starting from 18 January 18 to 10 March 2010. The third experiment was carried out at the two sites of progeny testing, namely the Kawasan Hutan Penelitian Dengan Tujuan Khusus (KHDTK), Sobang, Banten Province, and at Bintuni, West Papua Province during 22 months starting from February 2008 to December 2009. The results showed the average percentage of polymorphic loci (PPL) was 96.40% and the average genetic diversity (He) was 0.409. Total genetic diversity of merbau was still quite higher as shown by HT = 0.438. The genetic variation was mostly distributed within the population, namely 93.38 and 6.62% was distributed among the populations. The phylogenetic relationship among populations was four groups. The higher level of genetic diversity, among other, was caused by intermating among merbaus with the higher average value of hybridization at multiple loci (tm = 1.00), and the average value of hybridization at one locus (ts = 0.994), respectively. The rate of kinship mating was very low among merbaus, i.e. 0.006. The higher genetic diversity in the natural populations strongly supported the adaptability an d growth of merbau in the field. Results of evaluations and observations on the 18 month merbau plants in the Sobang and Bintuni showed that the life average percentages of individual plant were 91.64% and 98.37%, respectively. The estimates of heritability both individual and familial heritability values of the analysis results in the Sobang, Bintuni plot progeny testing and the combination of both were in the range of moderate and high levels for all three parameters, i.e. height, diameter and branching. The heritability value can still change with time and plant growth. Hence, the heritability range of moderate and high level can be used as early information for selection in the future. The computation of genetic correlations between height and diameter in this research was robust in the Sobang (rg = 0.96) and Bintuni (rg = 0,92) progeny testing and in the combination of those two sites (rg = 0,95). Based on the origin of the merbau population, there was early information about the positive correlation between the genetic diversity and the growth of plant in terms of its height, diameter and branching characteristics were 0.12, 0.10, and 0.20, respectively.

Kata Kunci : keragaman genetik , heritabilitas, Intsia bijuga, isoenzim