KAJIAN KERAGAMAN KOMUNITAS RIZOBAKTERI SEMANGKA: PENGARUH INFEKSI CUCUMBER GREEN MOTTLE MOSAIC VIRUS DAN KARAKTERISASI ISOLAT TERPILIH SEBAGAI PEMACU PERTUMBUHAN TANAMAN

Maharani Pertiwi K., Prof. Dr. Ir. Susamto Somowiyarjo, M.Sc

2012 | Tesis | S2 Bioteknologi

Rizobakteri merupakan bakteri yang hidup pada perakaran tumbuhan, sebagai bakteri bebas maupun bersimbiosis pada akar tanaman inang. Penelitian ini bertujuan untuk (1) menumbuhkan dan menganalisis populasi rizobakteri semangka menggunakan teknik aerob; (2) menganalisis komunitas rizobakteri aerob pada semangka yang diinfeksi Cucumber green mottle mosaic virus (CGMMV) secara buatan; (3) melakukan isolasi, pemilihan dan karakterisasi rizobakteri dari semangka sehat yang bersifat sebagai Rizobakteri Pemacu Pertumbuhan Tanaman (RPPT) berdasarkan sekuensing gen parsial 16S rRNA. Isolat rizobakteri dipilih berdasarkan kemampuannya dalam memproduksi Indol Acetic Acid (IAA), melarutkan fosfat, produksi gelatinase dan ammonia, pereduksi nitrat dan penghambatan jamur patogen. Komunitas rizobakteri dianalisis menggunakan metode Ribosomal Intergenic Spacer Analysis (RISA) yang bertujuan untuk membandingkan struktur komunitas rizobakteri pada tanaman sehat dan terinfeksi. Persentase kemiripan komunitas dianalisis berdasarkan pada profil pita–pita amplikon yang dihasilkan dari rDNA–RISA. Kemelimpahan relatif dari amplikon dianalisis menggunakan software NTSYS untuk mendapatkan persentase kemiripan berdasarkan pada ada atau tidaknya pita DNA. Komunitas rizobakteri pada tanaman sehat dan tanaman terinfeksi memiliki kemiripan 60%. Sebanyak enam isolat rizobakteri dipilih berdasarkan kemampuannya sebagai RPPT secara in vitro. Hasil pengamatan menunjukkan tiga isolat mampu menghasilkan IAA, lima isolat mampu melarutkan fosfat, dan seluruh isolat mampu menghidrolisis gelatin, dua isolat memiliki aktivitas menghambat Fusarium oxysporum fsp. melonis. Analisis gen 16S rRNA dan karakterisasi isolat terpilih menunjukkan homologi tertinggi dengan Burkholderia cepacia, Pantoea agglomerans, dan Pantoea ananatis.

Rhizobacteria is bacteria living in the rhizosphere either in free living state or symbiotic association. Both beneficial and deleterious rhizobacteria are present in the plant rhizosphere. The purposes of this study were (1) to cultivate and analyze rhizobacterial population in watermelon isolated by aerob technique; (2) to investigate aerob rhizobacterial community structure in watermelon rhizosfere under infection of Cucumber green mottle mosaic virus (CGMMV) by artificial inoculation; (3) to isolate and characterize multiple beneficial bacterial strains from healthy watermelon rhizosphere as plant growth promoting agens (PGPR) by partial sequencing 16S rRNA gene. The isolates were screened based on ability to produce IAA, phosphat–solublization, gelatinase, ammonia production, nitrat reduction and antifungal activity. Rhizobacterial communities were analyzed from healthy and infected plant. The result showed that highest population of rhizobacteria were found in healthy plant. Ribosomal Intergenic Spacer Analysis (RISA) were employed to compare rhizobacterial community structure in healthy and infected plant. Community percent similarity was analyzed based on banding profiles from rDNA–RIS amplicons. By incorporating the relative abundance of amplicons, the percentage of similarity determination was analyzed by similarity coefficients based only upon the absence or presence of DNA bands. Among the aerobic cultures, the greatest community (60% similarity) occurred in healthy plant and infected plant. A total of six isolates were selected based on their ability as PGPR in vitro. The results showed that three rhizobacteria isolates were able to produce indole acetic acid (IAA), five isolates were found to be able to solubilize insoluble phosphate, all isolates were showed to hydrolyze gelatine, and two rhizobacteria were found to posses antagonistic activity against Fusarium oxysporum fsp. melonis. 16S rRNA gene analysis from rhizobacteria isolates showed highly homology with Burkholderia cepacia, Pantoea agglomerans, and Pantoea ananatis.

Kata Kunci : CGMMV, RISA, Rizobakteri, RPPT, gen 16S rRNA