ANALISIS KERAGAMAN GENETIK Phytophthora capsici Leonian ASAL LADA (Piper nigrum L.) MENGGUNAKAN PENANDA MOLEKULER

ABSTRAK Phytophthora capsici adalah penyebab penyakit busuk pangkal batang yang paling merugikan pada lada di Indonesia dan sulit dikendalikan karena dapat bertahan lama dalam tanah serta memiliki keragaman agresivitas isolat luas. Pengetahuan mengenai keragaman genetik strain-strain P. capsici dapat membantu perancangan strategi efektif pengelolaan patogen. Penelitian ini bertujuan mengevaluasi keragaman dan struktur genetik isolat-isolat P. capsici asal lada menggunakan penanda RAPD. Penelitian dilaksanakan pada bulan Oktober 2009 sampai April 2010 di Laboratorium Biokimia BB Biogen dan Laboratorium Hama dan Penyakit Balittro. Keragaman genetik 59 isolat P. capsici yang berasal dari koleksi kultur tahun 1982-2009 dari 37 lokasi di Sumatera, Bangka, Jawa, dan Kalimantan, dikarakterisasi menggunakan enam primer RAPD. Pengelompokan menggunakan unweighted pair-group method with arithmatic averaging (UPGMA) berdasarkan profil RAPD membagi ke-59 isolat ke dalam lima gerombol utama; yang menunjukkan adanya keragaman genetik tinggi antar isolat. Pengelompokan RAPD tidak berkaitan dengan asal lokasi isolat. Analysis of molecular variance (AMOVA) juga menunjukkan adanya keragaman genetik yang tinggi di antara isolat-isolat P. capsici, dengan ragam genetik total sebesar 96% terletak di dalam masing-masing pulau (within populations). Namun demikian, terdapat ragam genetik antar isolat dari pulau berbeda (among populations) yang signifikan (4% ; P=0,001), yaitu antar populasi di Sumatera dan Bangka dengan jarak genetik sebesar 0,081 (P=0,002). Ketidakterkaitan antara pengelompokan RAPD dengan asal lokasi geografik isolat dan ragam genetik yang tinggi dalam satu pulau dapat diakibatkan oleh terjadinya penyebaran isolat antar daerah, terutama melalui bibit tanaman yang terinfestasi P. capsici. Pencegahan penyebaran isolat antar pulau perlu dilakukan melalui sertifikasi bibit bebas penyakit BPB dan pengembangan sistem perbenihan lokal. Kata kunci: lada, penyakit busuk pangkal batang, Phytophthora capsici, RAPD, keragaman genetik, struktur populasi ABSTRACT Phytophthora capsici is the causal agent of foot rot, the most destructive disease of pepper in Indonesia and difficult to control . Knowledge in the genetic structure of P. capsici strains can enrich designing effective disease management strategies. This study was aimed at analyzing the genetic variability and structure of P. capsici isolates from pepper using RAPD. The study was done from October 2009 until April 2010 at the Biochemical Laboratory of Indonesian Center for Agriculutral Biotechnology and Genetic Resources Research and Development, and the Plant Pest and Disease Laboratory of the Indonesian Research Institute of Spice and Medicinal Crops. Fifty-nine isolates collected from 1982 to 2009 from Sumatera, Bangka, Java, and Kalimantan were characterized based on six RAPD markers. Unweighted pair-group method with arithmatic averaging (UPGMA) clustering based on RAPD profiles divided the isolates into five major cluster, which indicated high genetic variability among isolates. No apparent relationship between RAPD clustering and geographic origin of isolate was observed. Hierarchical partitioning of genetic variation using analysis of molecular variance (AMOVA) confirmed the overall high variability among isolates, with 96% of total genetic variance was resided among isolates within islands (within populations). Nevertheless, a small (4%) but significant (P=0.001) genetic variance among isolates between different islands (among populations) were observed, which was detected between populations in Sumatera and Bangka with genetic distance (Ф PT ) as high as 0,081 (P=0,002). The lack of association between RAPD clustering and geographic origin as well as high genetic variance within populations may have been the result of movement of isolates between locations, most likely through infested plant cuttings. Use of certified and development of blackpepper clones locally are required to prevent disease spread among islands. Keywords: black pepper, foot rot disease, Phytophthora capsici, genetic diversity, RAPD, population structure