Karakterisasi fisiologi dan genetik pseudomonas sebagai biokontrol penyakit cendawan tular tanah pada tanaman kedelai

Abstract

Antagonist bacteria have been recognized playing important role in plant disease suppression. In Indonesia, the role and potential indigenous soybeans’ rhizobacteria such as antagonist Pseudomonas sp. as biocontrol have not many been reported. The aims of this study were to screen and characterize a number of Pseudomonas isolates as biocontrol agent against soilborne fungal pathogens i.e. Sclerotium rolfsii, Fusarium oxysporum or Rhizoctonia solani in soybean plants. Eleven isolates of Pseudomonas sp. CRB showed strong inhibition on the growth of the soilborne pathogenic fungi in vitro. Among of them, 7 isolates produced siderophore, 2 isolates produced chitinase, and 4 isolates produced hydrogen cyanide. Amplified rDNA restriction analysis (ARDRA) indicated high genetic diversity level since 7 ribotype groups were presented. 16S rRNA based sequences phylogenetic tree formed four clusters. There was a quite overlap among ARDRA groups and 16S rRNA clusters, suggested that in the same ARDRA group they were closely related to each other. The sequences of 16S rRNA gene confirmed that the isolates belonging to Pseudomonas sp. and similarity percentage varied to various species of Pseudomonas showed their extensive diversity. Part of antifungal biosynthesis gene encoding phenazine, phzF, phospho-2-dehydro-3-deoxyheptonate aldolase could be detected and confirmed in Pseudomonas sp. CRB-80 and CRB-102. Seed coating with the Pseudomonas sp. CRB demonstrated disease suppression in planta at approximately 14-100% in sterile soil and 5-53% in non-sterile soil. Pseudomonas sp. CRB-16, CRB-44, CRB-86, CRB-102 and CRB-109 which maintained moderate disease suppression, more than 30% in non-sterile soil might be considered for development as biological control agents to protect soybean from the soilborne fungal disease. Population density in soybean rhizosphere of Pseudomonas sp. CRB-17, CRB-80 and CRB-102 Rifr were 102-107 cells/g fresh root weight in sterile soil, in contrast to 0-106 cells/g fresh root weight in non-sterile soil for 6 weeks observation.

Proteksi tanaman modern sangat bergantung pada penggunaan bahan kimia untuk mengatasi hama dan penyakit. Akan tetapi, meningkatnya perhatian terhadap kesehatan dan kerusakan lingkungan yang disebabkan oleh penggunaan bahan kimia untuk pertanian menyebabkan peningkatan tuntutan yang lebih besar terhadap pertanian yang berkelanjutan. Pada tanah yang menekan penyakit dan kompos, penekanan penyakit diperoleh tanpa penggunaan bahan kimia. Penekanan penyakit selalu berhubungan dengan keberadaan bakteri antagonis yang jumlahnya semakin meningkat di dalam tanah. Bakteri rizosfer antagonis yang bermanfaat ini dapat dikembangkan sebagai agen pengendali biologi untuk mengurangi penggunaan bahan kimia di bidang pertanian. Di Indonesia, bakteri antagonis asli rizosfer tanaman kedelai belum banyak dilaporkan dan potensinya sebagai agen biokontrol perlu diteliti lebih lanjut. Tujuan penelitian ini adalah untuk mendapatkan kandidat agen biokontrol terhadap cendawan patogen tular tanah Sclerotium rolfsii, Fusarium oxysporum atau Rhizoctonia solani untuk tanaman kedelai.