ABSTRAK
Hawar daun bakteri (HDB) yang disebabkan oleh bakteri Xanthomonas oryzae pv. oryzae (Xoo) merupakan penyakit yang paling banyak menyerang padi. Biokontrol merupakan salah satu alternatif pengendalian HDB yang ramah lingkungan. Penelitian ini bertujuan untuk menyeleksi bakteri filosfer padi yang bersifat antagonis terhadap Xoo, mendeteksi gen polyketide synthase (PKS) pada DNA genom bakteri antagonis, mengidentifikasi golongan senyawa bioaktif dan menguji aktivitas anti-Xoo ekstrak senyawa bioaktif.
Bakteri diisolasi dari daun padi dan diuji kemampuan antagonisnya terhadap Xoo dengan menggunakan uji dual plate, kemudian dilakukan uji hipersensitivitas dan uji patogenisitas. Bakteri antagonis terpilih diidentifikasi berdasarkan karakter morfologi koloni dan sel serta gen penyandi 16S rRNA. Deteksi gen PKS dilakukan dengan menggunakan primer degKS2F.gc dan degKSR5.gc. Ekstraksi senyawa bioaktif dilakukan dengan metode ekstraksi bertingkat menggunakan pelarut n-heksan, etil asetat, dan metanol. Identifikasi golongan senyawa bioaktif dilakukan dengan menggunakan kromatografi kolom dan spektrofotometer UV-VIS. Uji aktivitas anti-Xoo ekstrak senyawa bioaktif dilakukan dengan menggunakan metode difusi cakram.
Hasil penelitian ini menunjukkan bahwa bakteri filosfer padi yang bersifat antagonis terhadap Xoo adalah bakteri Pseudomonadaceae SH2a yang menghasilkan senyawa bioaktif golongan poliketid (pyoluteorin dan 2,4-diacetylphloroglucinol), penazin, pirrolnitrin, peptida, terpenoid, alkaloid, serta lipopeptida; Pantoea sp. MO142; Pantoea sp. MO22g; Erwinia sp. MO34h; Pantoea sp. MO34i; Pantoea sp. MO34j; Pantoea sp. MO43a; serta Pantoea sp. MO63j yang menghasilkan senyawa bioaktif golongan poliketid, peptida, terpenoid, alkaloid, serta lipopeptida. Gen PKS dapat terdeteksi pada DNA genom Pantoea sp. MO22g, Erwinia sp. MO34h, Pantoea sp. MO34i, Pantoea sp. MO34j, serta Pantoea sp. MO43a. Ekstrak senyawa bioaktif bakteri antagonis yang memiliki aktivitas anti-Xoo adalah ekstrak kasar dan fraksi metanol bakteri Pseudomonadaceae SH2a; ekstrak kasar dan fraksi n-heksan Pantoea sp. MO22g, Pantoea sp. MO43a, dan Pantoea sp. MO63j; ekstrak kasar Erwinia sp. MO34h dan Pantoea sp. MO34j; ekstrak kasar, fraksi etil asetat, dan fraksi n-heksan Pantoea sp. MO34i.
Kata kunci: filosfer, padi, biokontrol, Xanthomonas oryzae pv. oryzae (Xoo), antagonis, hawar daun bakteri
ABSTRACT
Bacterial leaf blight (BLB) was caused by Xanthomonas oryzae pv. oryzae (Xoo) is the most commonly attacking rice disease. Therefore we introduced an alternative approach to control the BLB by using biocontrol agents that environment-friendly. The aims of this study were to (i) select rice phyllosphere bacteria antagonistic against Xoo, (ii) detect polyketide synthase (PKS) gene from genomic DNA of antagonist bacteria (iii) identify the groups of bioactive compounds and (iv) test the anti-Xoo activity bioactive compounds extract.
Bacteria were isolated from rice leaves and antagonistic ability against Xoo was tested using a dual plate method, and then hypersensitivity and pathogenicity test were conducted respectively. The selected antagonist bacteria were identified based on type of colonies and the morphological character cell, and as well as genes encoding 16S rRNA. Detection of PKS gene was performed using primer degKS2F.gc and degKSR5.gc, while extraction of bioactive compounds was carried out under stratified extraction using n-hexane, ethyl acetate, and methanol solvent respectively. Column chromatography and UV-VIS spectrophotometer were used to identify groups of bioactive compounds. Disc diffusion method was used to look at anti-Xoo activity of bioactive compounds extract.
The results showed that rice phyllosphere bacteria antagonistic against Xoo were Pseudomonadaceae SH2a bacterium which produced bioactive compounds polyketide (pyoluteorin and 2,4-diacetylphloroglucinol), phenazine, pyrrolnitrin, peptides, terpenoids, alkaloids, and lipopeptide groups. In addition Pantoea sp. MO142, Pantoea sp. MO22g, Erwinia sp. MO34h, Pantoea sp. MO34i, Pantoea sp. MO34j, Pantoea sp. MO43a, and Pantoea sp. MO63j produced bioactive compounds polyketide, peptides, terpenoids, alkaloids, and lipopeptide groups. Polyketide synthase gene was detected from genomic DNA Pantoea sp. MO22g, Erwinia sp. MO34h, Pantoea sp. MO34i, Pantoea sp. MO34j, and Pantoea sp. MO43a. Bioactive compounds extract from antagonist bacteria that have anti-Xoo activity is crude extracts and methanol fractions Pseudomonadaceae SH2a bacterium; crude extract and n-hexane fractions Pantoea sp. MO22g, Pantoea sp. MO43a, and Pantoea sp. MO63j; crude extract of Erwinia sp. MO34h and Pantoea sp. MO34j; crude extract, ethyl acetate fractions and n-hexane fraction Pantoea sp. MO34i.
Keywords: phyllosphere, rice, biocontrol, Xanthomonas oryzae pv. oryzae (Xoo), antagonist, bacterial leaf blight