Potensi Rhizobium ISOLAT Mucuna bracteata DC. dalam Menghambat Pertumbuhan Ganoderma boninense Pat. dan Menghasilkan IAA (INDOLE-3-ACETIC ACID)

Abstract

Efforts to control basal stem rot disease of oil palm caused by Ganoderma boninense are still continued to be carried out, i.e by application of antagonistic biological control agents against G. boninense, such as Rhizobium. The aim of this study was to obtain the antagonistic species of Rhizobium from root nodules of Mucuna bracteata against G. boninense, to determine their antagonistic mechanisms and their potency to produce Indol acetic acid (IAA) growth regulator Rhizobium was isolated from the root nodules of M. bracteata that was cultivated in Aek Pancur oil palm plantations, in North Sumatra province. Rhizobium isolated from root nodules by breaking-out the nodules and then cultivated it on specific medium of Yeast Extract Mannitol Agar (YEMA). The isolated bacterial were characterized and identified molecularly, find out their antagonistic activity and mechanisms against G. boninense, and their ability to produce IAA. The results showed that isolation and characterization of bacteria from root nodules of M. bracteata were obtained 3 candidates isolates of Rhizobium. Molecular identification showed that the three isolates were positive species of Rhizobium with a high percentage of similarity index with Rhizobium sp. Strain J007 was 97-98%. However, it is suspected to be a type of Rhizobium leguminosarum strain SmrVr -115 based on the results of the phylogenetic tree construction. The antagonistic test of three species of Rhizobium against G. boninense with dual culture test resulted in the percentage of mycelium inhibition value in a range of 43.33%-66.7%. The antagonistic mechanisms of 3 species of Rhizobium against G. boninense were shown by producing antifungal compounds with the percentage 11,67-27% glucanolytic mechanisms with the index of glunacanolitics 0,25-0,4. but none of chitinolytic activity. All species of Rhizobium are able to produce IAA with the concentration of IAA 1,166-23,66.

Upaya pengendalian penyakit busuk pangkal batang pada kelapa sawit yang disebabkan oleh jamur Ganoderma boninense terus dilakukan antara lain dengan memanfaatkan agen pengendalian hayati yang bersifat antagonis terhadap jamur G. boninense seperti Rhizobium yang terdapat pada tanaman Mucuna bracteata. Penelitian ini bertujuan untuk mendapatkan jenis Rhizobium dari bintil akar M. bracteata yang berpotensi antagonis terhadap G. boninense, mengetahui mekanisme antagonis dan kemampuan menghasilkan zat pengatur tumbuh IAA (Indole-3-Acetic Acid). Rhizobium diisolasi dari bintil akar tanaman M. bracteata dari perkebunan sawit daerah Aek Pancur provinsi Sumatera Utara. Bakteri diisolasi dengan memecah bintil akar dan menumbuhkannya pada media spesifik Yeast Extract Mannitol Agar (YEMA). Isolat bakteri yang diperoleh kemudian dikarakterisasi dan diidentifikasi secara molekuler lalu duji kemampuan antagonisnya terhadap G. boninense, dipelajari mekanisme antagonis, serta kemampuan menghasilkan IAA. Hasil isolasi bakteri dari bintil akar M. bracteata diperoleh sebanyak 3 isolat yang menunjukkan karakter sebagai bakteri dari genus Rhizobium. Identifikasi secara molekuler menunjukkan bahwa ketiga isolat tersebut benar Rhizobium dengan persentase kesamaan yang tinggi dengan Rhizobium sp. Strain J007 yaitu sebesar 97-98%. Namun, diduga merupakan jenis Rhizobium leguminosarum strain SmrVr -115 berdasarkan hasil konstruksi pohon filogenetik. Uji antagonis ketiga bakteri Rhizobium tersebut terhadap G. boninense menghasilkan persentase hambatan miselium sebesar 43,33%-66,7%. Ketiga Rhizobium menunjukkan mekanisme penghambatan terhadap G. boninense berupa produksi senyawa antijamur dengan persentase 11,67-27% dan produksi enzim glukanolitik dengan indeks glukanolittik 0,25-0,4. Namun, tidak ditemukan kemampuan kitinolitik. Ketiga Rhizobium mampu menghasilkan IAA dengan konsentrasi IAA 1,166-23,66.