Uji Laboratorium Azospirillum sp. yang Diisolasi dari Beberapa Ekosistem

S Widawati, Agus Muharam

Abstract


ABSTRAK. Beberapa mikrob yang bersifat nonpatogenik dan nonsimbiotik yang efektif menambat nitrogen dari udara serta mampu melarutkan P terikat pada Ca, Al, dan Fe dalam tanah, dapat hidup dalam berbagai ekosistem di alam. Sebagian bakteri tersebut dapat diisolasi dari daerah perakaran tanaman hortikultura. Penelitian bertujuan mengetahui peran Azospirillum sp. yang potensial sebagai pendorong pertumbuhan tanaman pada ekosistem pantai dan kondisi lingkungan yang ekstrim. Pengujian terhadap isolat bakteri yang dikumpulkan dari berbagai kondisi ekosistem dilaksanakan di Laboratorium Ekofisiologi, Pusat Penelitian Biologi, LIPI, Bogor dari Bulan Januari sampai dengan Desember 2011. Sebanyak 34 isolat Azospirillum sp. diuji dengan berbagai metode, yaitu (1) uji kualitatif kemampuan isolat Azospirillum sp.  dalam menambat (fiksasi) nitrogen dan kemampuan hidup pada media Okon padat yang mengandung NaCl, (2) uji kualitatif kemampuan isolat Azospirillum sp. dalam melarutkan P terikat pada  Ca3(PO4)2 dalam media  Pikovskaya padat dan indeks efisiensi pelarutan fosfat,  (3) uji kualitatif kemampuan isolat Azospirillum sp. dalam melarutkan P terikat pada media  Pikovskaya cair  dan aktivitas enzim PME-ase asam dan basa, serta kondisi pH selama inkubasi 7 hari pada kultur murni (pH asal= 7), dan (4) analisis kemampuan Azospirillum sp. dalam memproduksi indole acetic acid (IAA).  Hasil penelitian menunjukkan bahwa: (1) semua isolat bakteri yang diuji mampu menambat nitrogen dalam media Okon padat,  (2) isolat B2, B4, B6, B12,  B14, PS2, dan FR13 mampu melarutkan P dari Ca3(PO4)2 dalam medium Pikovskaya padat dengan masing-masing indeks efisiensi pelarutan sebesar  120, 160, 140, 100, 110, 120, dan 100,  (3) isolat B1, B2, B3, B4, B6, B14, B17, PS1, PS2, PS3, FR1, FR5, FR7, FR8, FR10, FR12, dan FR13 mampu tumbuh dalam medium Okon dengan kandungan NaCl sebesar 0, 2, 4, atau 6%, (4)  konsentrasi tertinggi P terlarut dihasilkan oleh isolat B4 (5,80 mg/l), B6 (5,84 mg/l), dan PS2 (5,45 mg/l) dengan PME-ase sebesar 0,58 u m/l, 0,58 u m/l, 0,57 u m/l (asam), 0,52 mg/l, 0,50 mg/l, 0,48 mg/l (basa), dan dengan  pH : 4,20, 4,30, dan 4,22,  dan (5) isolat B4 dan B6 yang diisolasi dari pertanaman padi di pantai Rambut Siwi, Bali, mampu memproduksi IAA tertinggi, yaitu masing-masing sebesar 0,6749 dan 0,4694 ppm pada hari pertama setelah perlakuan. Berdasarkan hasil penelitian ini terbukti bahwa isolat Azospirillum sp. berpotensi sebagai plant growth promoter  untuk ekosistem di daerah pesisir atau pantai. Bakteri tersebut sangat penting untuk pengkayaan nutrisi pada lahan di daerah dataran rendah atau pantai dalam rangka pengembangan tanaman termasuk komoditas hortikultura.

ABSTRACT. Widawati, S and Muharam, A 2012. The Laboratory  Test of  Azospirillum sp. Isolated  from Several  Ecosystems. Microbes that are nonpathogenic  and nonsymbiotic bacteria which are effectively fixed up nitrogen from air, and are able to dissolve phosphated bounded on Ca, Al, and Fe in soil, are able to growth in different ecosystems in nature. Some of the bacterial species can be isolated from rizosphere of horticultural crops. The research was aimed to determine the potential role of Azospirillum sp.  as a plant growth promoter in coastal ecosystem and extremely environmental conditions. The laboratory test of Azospirillum sp. isolated from several ecosystems was carried out in the Ecophysiology Laboratory, Research Center for Biology, Indonesian Institute of Sciences, Bogor from January until December 2011. Thirty-four isolates of Azospirillum sp. (B1 to B17;PS1 to PS3; FR1 to FR 14) were investigated with some methods i.e. (1) the qualitative test of the capability of Azospirillum sp. to fix up nitrogen in solid Okon medium containing NaCl, (2) the qualitative test of the capability of Azospirillum sp. in dissolving bounded P in solid Pikovskaya medium and phosphate dissolution efficiency index,  (3) the qualitative test of the capability of Azospirillum sp. in dissolving bounded P in liquid Pikovskaya medium and the activity of acid and base PME-ase, and pH condition after 7 days incubation in pure media, and (4) analysis of the capability of Azospirillum sp. in producing indole acetic acid (IAA).  The results pointed out that : (1) all tested isolates of Azospirillum sp. were  capable to fix up nitrogen in solid Okon medium, (2) isolates of B2, B4, B6, B12,  B14, PS2, and FR13 were capable to solubilize P on Ca3(PO4)2 in solid Pikovskaya medium with its efficiency of  120, 160, 140, 100, 110, 120, and 100, respectively, (3) isolates of B1, B2, B3, B4, B6, B14, B17, PS1, PS2, PS3, FR1, FR5, FR7, FR8, FR10, FR12, and FR13 were able to grow in Okon medium with 0, 2, 4, or 6% of NaCl doses, (4) the highest concentrations of solubilized P was resulted by isolates B4 (5.80 mg/l), B6 (5.84 mg/l), and PS2 (5.45 mg/l) with PME-ase i.e. 0.58 u m/l, 0.58 u m/l, 0.57 u m/l (acid), 0.52 mg/l, 0.50 mg/l, 0.48 mg/l (base), and with pH : 4.20, 4.30, and 4.22, and (5) isolates of B4 and B6 isolated from rice field at Rambut Siwi beach, Bali, were capable to produce highest IAA hormone i.e. 0.6749 and 0.4694 ppm respectively  on the first day after the treatment. Based on the result of this experiment it can be concluded that Azospirillum sp. is a potential plant growth promoting Rhizobacteria for coastal ecosystem. The bacterial species is very important to enrich coastal areas for crop cultivation, including horticulture.


Keywords


Azospirillum; IAA; Phosphate solubilizing bacteria; Nitrogen fixing bacteria, Plant growth promoting rhizobacteria

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DOI: http://dx.doi.org/10.21082/jhort.v22n3.2012.p258-267

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