Potensi bakteri penghasil senyawa bioaktif anticendawan untuk pengendalian penyakit hawar pelepah padi

Abstract

The objectives of this research were to (i) screen some potential bacteria as biological control agents of the sheath blight disease caused by R. solani, (ii) identify character of the selected bacteria strains as biological control agents, and (iii) characterize the antifungal activities of the antifungal bioactive compound produced by the selected strains against R. solani. The antagonist bacteria were isolated from rhizospheric soil, rice plant, and pond water collected from several locations. Screening of bacteria strains on the growth inhibition of R. solani was conducted in the laboratory, while the selection of bacteria for their effectiveness to suppress sheath blight disease were done in the screen house. The result of this research showed that there are three bacterial isolates which antifungal activity significantly suppressed the rice sheath blight disease, i.e. TT47, SS19, and BR2 with suppression ability of 79,6, 56,4, and 49,47%, respectively. Molecular analysis of partial sequence of 16S rRNA showed that SS19, TT47, and BR2 isolates were Serratia marcescens, Ralstonia pickettii, and Bacillus subtilis, respectively. These biocontrol agents are not phythotoxic, produce siderophore, and phosphate-solubilizing. S. marcescens SS19 and R. pickettii TT47 were chitin-degrading bacteria but B. subtilis BR2 was not. The filtrate from fermentation broth of the R. pickettii TT47 and B. subtilis BR2 inhibited the growth of R. solani. The antifungal bioactive compound was relatively stable on pH range from acidic to basic (pH 4, pH 7, and pH 10). The optimum activity of antifungal bioactive compound was at room temperature (25-27 0C) and tend to decrease at higher temperature (60, 80. 100, and 121 0 Key words: The rice sheath blight, antifungal bioactive compounds, Serratia marcescens, Ralstonia pickettii, Bacillus subtilis. C). The antifungal activity of hexane extract of R. pickettii TT47 and ethyl acetate extract of B. subtilis BR2 in vitro revealed significant growth inhibition to R. solani, respectively by 86,3% and 77,8%. MIC of hexane extract and ethyl acetate extract were 0,1 mg/l and 10 mg/l respectively, and both extracts are not phythotoxic against the rice seedling.

Padi merupakan komoditas strategis nasional. Lebih dari 90% penduduk Indonesia menjadikan padi sebagai sumber makanan pokok. Untuk itu upaya peningkatan produksi perlu terus dilakukan agar kebutuhan penduduk yang jumlahnya terus meningkat dapat terpenuhi. Namun tantangan peningkatan produksi di masa yang akan datang diprediksi juga makin meningkat terkait dengan perubahan iklim dan ancaman serangan hama atau patogen tanaman. Penyakit hawar pelepah yang disebabkan oleh cendawan R. solani merupakan salah satu penyakit penting pada tanaman padi. Infeksi patogen menyebabkan gejala bercak berukuran besar pada pelepah dan daun bahkan dapat menyebabkan kematian pada seluruh bagian daun. Patogen memiliki kisaran inang yang luas dan hingga saat ini belum tersedia varietas tanaman padi yang benar-benar tahan. Patogen mampu bertahan dalam tanah dan sisa-sisa tanaman dalam bentuk sklerotia atau miselium. Untuk itu pengendalian dengan menggunakan agens hayati perlu dikembangkan. Penelitian ini bertujuan (i) mendapatkan isolat bakteri sebagai agens hayati yang dapat mengendalikan penyakit hawar pelepah padi yang disebabkan oleh R. solani, (ii) mengarakterisasi sifat unggul agens hayati dan mengidentifikasi isolat bakteri terpilih, (iii) menentukan karakteristik senyawa bioaktif anticendawan yang dihasilkan isolat bakteri terpilih.