Studi Fisiologi dan Molekular Klon Karet (Hevea brasiliensis Muell. Arg.) IRR Seri 400 sebagai Batang Atas terhadap Cekaman Kekeringan

Abstract

Drought stress is the main cause of plant death. Strategies for plants to survive in the stress conditions include adaptation of morphological development, specific signaling pathways to defense conditions and the formation of an immune system for plants. Rubber plantations have many advantages, including sources of foreign exchange, employment sources, reforestation and revitalization, as well as forest wood substitution for building materials and household furniture. The response of rubber plants to drought stress is a complex biological process. Indonesia has a large dry land area of around 122.1 million ha, which has not been optimally utilized due to limited water resources. Planting drought tolerant rubber clones is the right approach. Unit Research Sungei Putih, Indonesian Rubber Research Institute since 1985 has been assembling superior rubber clones with hand pollination techniques. One of them, from the hybridization results in 1993-1996 selected several genotypes called IRR 400 series clones have high growth and latex production (average > 45 gram/tree/tapping). Adapt to drought environment, it is necessary to understand the mechanism of tolerance (escape, avoidance, tolerance). The study was designed with some of water content (30%, 60%, 90% FC) to seven promissing rubber clones (IRR 425, IRR 428, IRR 429, IRR 434, IRR 440, RRIC 100, BPM 24). Four stages of activities have been carried out to support the major title of this dissertation, namely 1. selection of drought tolerance of GT1 rubber seedlings with the addition of polyethylene glycol (PEG) 6000. 2. estimated compatibility of IRR 400 series as promising rubber clones with GT1 rootstock based on growth characteristics, 3. leaf characterization of rubber clones IRR 400 series, BPM 24, and RRIC 100 using the leafgram method, 4. physiological and molecular characters of rubber clones IRR 400 series as scions to drought stress. The research was carried out from April 2020 to May 2021 which was carried out in the budwood garden, greenhouse, physiology and protection laboratory of the Unit Research Sungei Putih, Sungei Putih Loka Ternak laboratory and the molecular laboratory of PT. Socfin Indonesia Bangun Bandar, Dolok Masihul. The first study results showed that the character of the rate of increase in taproot length was a distinguishing character that indicated the initial tolerance level of GT1 seedlings to drought with a sensitivity index value of taproot growth rate, the ratio of taproot length and shoot height was classified as moderate (7.5%). The second study results showed that the compatibility between the IRR 400 series as scion and GT1 as rootstock was indicated by three characters (initial indicators), namely shoot height, petiole length and whorl distance. This result is strengthened by the correlation (r>0.8) and heritability value (h2>0.5). The third study results showed that there were eleven distinguishing characters that could be used in the identification and characterization the leaves of the IRR 400 series, RRIC 100 and BPM 24 clones which were assessed as differentiating from one clone to another by quantification, namely leaf width (cm), left blade width (cm), apex angle (o), basal angle (o), left blade width/leaf fold ratio, left blade width/center point ratio, pointto- fold /leaf area ratio, fold point/leaf area ratio, angle leaf apex/basal ratio, leaf vein/apex angle ratio, leaf vein and leaf apex angle ratio, leaf vein/basal angle ratio). These characters also have high heritability values (h2>0.5). The fourth study results showed total sugar and proline characters could be used as initial identification in assessing tolerance mechanism in the IRR 400 series rubber clones which was also supported by the presence of ITS-1 primer which could illustrate that there was diversity in the treatment. The conclution of this study is early assessment and selection of IRR 400 series hopeful clones has been carried out comprehensively by assessing various main and supporting factors to be adapted to the actual environment.

Cekaman kekeringan merupakan penyebab utama kematian suatu tanaman. Strategi bagi tanaman untuk bertahan pada kondisi tercekam diantaranya adalah perkembangan adaptasi morfologi, adanya jalur sinyal spesifik terhadap kondisi pertahanan dan terbentuknya sistem kekebalan bagi tanaman. Perkebunan karet memiliki banyak kegunaan, diantaranya sumber devisa negara, sumber lapangan pekerjaan, tanaman reboisasi dan revitalisasi hutan, serta bahan subtitusi kayu hutan untuk material bangunan dan perabot rumah tangga. Respon tanaman karet terhadap cekaman kekeringan adalah proses biologis kompleks. Indonesia memiliki lahan kering cukup luas sekitar 122,1 juta ha, dan belum optimal termanfaatkan akibat keterbatasan sumber air. Penanaman klon karet toleran kering merupakan pendekatan tepat. Unit Riset Sungei Putih, Pusat Penelitian Karet sejak tahun 1985 telah melakukan perakitan klon karet unggul dengan teknik persilangan buatan. Salah satunya, dari hasil persilangan (HP) tahun 1993- 1996 terseleksi beberapa genotipe yang dinamakan klon IRR seri 400 memiliki pertumbuhan dan produksi lateks tinggi (>45 gram/pohon/sadap). Untuk beradaptasi dilingkungan kering, perlu dipahami mekanisme toleransi (escape, avoidance, tolerance). Penelitian didesain dengan perlakuan beberapa kadar air (30%, 60%, 90% KL) pada tujuh klon karet unggul harapan (IRR 425, IRR 428, IRR 429, IRR 434, IRR 440, RRIC 100, BPM 24). Empat tahapan kegiatan yang telah dilakukan untuk mendukung judul besar disertasi, yaitu 1. Seleksi toleransi kekeringan bibit karet GT1 dengan penambahan polietilen glikol (PEG) 6000. 2. Dugaan kompatibilitas klon karet harapan IRR seri 400 dengan batang bawah GT1 berdasarkan karakter pertumbuhan, 3. Karakterisasi daun klon karet IRR seri 400, BPM 24, dan RRIC 100 menggunakan metode leafgram, 4. Karakter fisiologi dan molekular klon karet IRR seri 400 sebagai batang atas terhadap cekaman kekeringan. Penelitian dilakukan sejak bulan April 2020 sampai Mei 2021 dilaksanakan di kebun entres, rumah kaca, laboratorium fisiologi dan proteksi Unit Riset Sungei Putih, laboratorium Loka Ternak Sungei Putih dan laboratorium molekular PT. Socfin Indonesia Bangun Bandar, Dolok Masihul. Hasil penelitian pertama menunjukkan bahwa karakter laju pertambahan panjang akar tunggang merupakan karakter pembeda tingkat toleransi awal bibit GT1 terhadap kekeringan dengan nilai indeks sensitivitas laju pertambahan akar tunggang, rasio panjang akar tunggang dan tinggi tunas tergolong sedang (7,5%). Hasil penelitian kedua menunjukkan kompatibilitas antara batang atas klon IRR seri 400 dan batang bawah GT1 ditunjukkan oleh tiga karakter, yaitu tinggi tunas, panjang tangkai daun dan jarak antar payung. Hasil ini diperkuat dengan nilai korelasi (r>0,8) dan heretabilitas (h2>0,5). Hasil penelitian ketiga menunjukkan bahwa ada sebelas karakter pembeda untuk identifikasi klon IRR seri 400, RRIC 100 dan BPM 24 yaitu lebar daun (cm), lebar helaian kiri daun (cm), sudut apeks (o), sudut basal (o), rasio lebar helaian kiri/titik lipat daun, rasio lebar helaian kiri/titik pusat, rasio titi lipat/luas daun, rasio titik lipat/luas daun, rasio sudut apeks/basal daun, rasio sudut vena/apeks daun, rasio sudut vena dan apeks daun, rasio sudut vena/basal daun, dengan nilai heretabilitas tinggi (h2>0,5). Hasil penelitian keempat menunjukkan bahwa karakter gula total dan prolin dapat dijadikan sebagai identifikasi awal dalam menilai mekanisme toleransi pada klon karet IRR seri 400 dan didukung oleh data primer ITS-1 yang menggambarkan keragaman dalam perlakuan. Sehingga dari penelitian ini dapat disimpulkan bahwa penilaian dan seleksi terhadap klon harapan IRR seri 400 secara awal sudah dilakukan secara komprehensip dengan menilai berbagai faktor utama dan pendukung untuk dapat diadaptasikan kelingkungan yang sebenarnya.