Peningkatan produksi tanaman padi salah satunya  dengan cara pemupukan. Penggunaan pupuk kimia dapat menimbulkan dampak negatif, sehingga dikembangkan sistem pertanian organik.  Rhizoctonia solani  merupakan cendawan patogen yang menyerang tanaman padi, sehingga dapat menurunkan produksi tanaman padi. Bakteri rizosfer dapat menghasilkan senyawa yang dapat menghambat pertumbuhan cendawan patogen. Penelitian ini bertujuan untuk mengisolasi dan menguji aktivitas penghambatan bakteri rizosfer tanaman padi (Oryza sativa) dari sawah organik di Kecamatan Mojosongo Kabupaten Boyolali terhadap cendawan patogen Rhizoctonia solani sebagai penelitian awal untuk pengembangan pupuk hayati. Pengambilan sampel tanah rizosfer dilaku kan di Kecamatan Mojosongo yaitu kawasan sawah organik Pangudi Bogo, Pangudi Raharjo, dan Budi Rahayu. Bakteri rizosfer diisolasi dari tanah rizosfer tanaman padi organik dengan metode streak di media NA. Cendawan patogen diisolasi dari tanaman padi yang terindikasi penyakit yang disebabkan oleh  Rhizoctonia solani yang ditanam di media PDA. Uji antagonisme bakteri rizosfer terhadap Rhizoctonia solani dilakukan dengan metode dual culture secara in vitro. Dari penelitian ini 12 isolat bakteri didapatkan. Empat diantara 12 isolat  memiliki aktivitas penghambatan terhadap cendawan patogen  Rhizoctonia solani  yaitu A5, B1, C1, dan C2. Hasil uji  antagonis menunjukkan persentase penghambatan isolat bakteri rizosfer  C1 sebesar 70%, C2 sebesar 52,22% , isolat A5 sebesar 44,44% , dan B1 sebesar 27,78%.

Kata kunci:  uji antagonis, rizosfer, padi, Rhizoctonia solani, sawah organik

Fertilizing is a method to increase the production of rice. The use of chemical fertilizer causes negative effects. Organic farming is developed to minimalize it. Rhizoctonia solani is a pathogen fungus which attacks rice plant. It can be used to reduce rice production. Rhizospher bacteria producing inhibitor component for the growth of pathogen fungus. This study aims to isolate and test  the inhibit activity of rhizospher bacteria in rice plant (Oryza sativa) from organic field at Mojosongo, Boyolali, toward pathogen fungus R. solani as an early research to develop a biofertilizer. Rhizospher soil sampling was done at organic fields in Mojosongo, there were Pangudi Bogo, Pangudi Raharjo, and Budi Rahayu. Rhizospher bacteria were isolated from the organic rice soil with streak method in Nutrient Agar (NA) media. Pathogen fungus were isolated from sick rice plant causes by R. solani and grew in PDA media. Antagonism test of rhizospher bacteria toward R. solani was done with dual culture in vitro method. 12 bacteria were isolated from the soil. Four of it had inhibit activity toward pathogen fungus R. solani, there were A5, B1, C1, and C2. The result of antagonism test showed the inhibit activity percentages of rizospher bacteria C1 was 70%, C2 was 52.22%, A5 was 44.44%, and B1 was 27.78%.

Keywords: antagonism test, rhizospher, rice, Rhizoctonia solani, organic field