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Abstract. Wahyudi AT, Priyanto JA, Fijrina HN, Mariastuti HD, Nawangsih AA. 2019. Streptomyces spp. from rhizosphere soil of maize with potential as plant growth promoter. Biodiversitas 20: 2547-2553. Actinomycete is one group of rhizobacteria that plays an important role as a plant growth promoter. This study was aimed to evaluate the potential of Actinomycetes isolated from maize rhizosphere in promoting plant growth in vitro including their ability to produce IAA, promote maize sprout growth, solubilize phosphate, and grow in N-free medium. Thirty isolates have been isolated from maize rhizosphere using a spread plate method. All 30 isolates were probably not pathogenic to plants as tested by hypersensitivity reaction test on tobacco leaves. Based on the colorimetric assay, 30 isolates (100%) were able to produce IAA with concentrations ranging from 1.05 to 26.89 ppm. The highest concentration of IAA (26.89 ppm) produced by ARJ 21 and the lowest IAA concentration (1.05 ppm) produced by ARJ 12. By using the Ragdoll method, it showed that 9 isolates (30%) were able to promote maize sprout growth significantly on five growth parameters including primary root length, stem length, number of lateral roots, wet weight and dry weight. Twenty-one isolates (70%) were capable of solubilizing phosphate in Pikovskaya medium containing tricalcium phosphate. Also, 30 isolates (100%) were able to grow on N-free medium, suggesting their ability to fix nitrogen. Based on 16S-rRNA, five potential isolates with plant growth-promoting properties were highly similar to Streptomyces spp. Based on their potential characters, these Actinomycetes isolates have the potential to be further developed as a biofertilizer agent for sustainable maize farming.

Abstract. Fatmawati U, Meryandini A, Nawangsih AA, Wahyudi AT. 2019. Screening and characterization of actinomycetes isolated from soybean rhizosphere for promoting plant growth. Biodiversitas 20: 2970-2977. Actinomycetes which colonized plant rhizosphere has a vital role in improving plant growth by producing Indole-3-Acetic Acid (IAA). The aim of this study was to evaluate the potency of actinomycetes isolated from soybean rhizosphere as promoter agents for plant growth in vitro. Fifty actinomycetes isolates were successfully isolated from soybean rhizosphere. Based on the colorimetric methods, 35 isolates can produce IAA in various concentration, in the range of 0.46-30.6 mg/L. Seed germination assay using Ragdoll methods revealed that 26 isolates significantly promoted germination parameters, including the hypocotyl and the radicular length, the number of the lateral roots, and dry weight of the plant. Also, 14 from 26 isolates showed phosphate solubilizing activity in different phosphate-solubilizing index ranging from 1.25-2.62. Eight isolates were able to grow in N-free medium, indicating that these isolates have the ability in fixing nitrogen. Out of 23 from 26 isolates were detected to produce siderophore. All the tested isolates show chitinase production except ASR 55. Based on the observed parameters, it showed that there are four potential isolates (ASR 46, ASR 58, ASR 75 and ASR 76) as promising plant-growth promoters, phosphate solubilizer, nitrogen fixer, siderophore and chitinase producer. Based on the result of 16S rRNA sequence analysis, four potential isolates were identified as Streptomyces spp. in different taxa of strains and species.

Liquid smoke is reported to be effective to inhibit some bacteria. The study aimed to evaluate the effects of liquid smoke (LS) from coconut shell (CS-LS), pinecone (P-LS), and oil palm branch (OPB-LS) on the incidences of blood disease, induced resistance to Ralstonia syzygii subsp. celebesensis, and plant growth. Two days after banana seedlings were treated with LS, ethylene, auxin, lignin, activities of the enzymes of peroxidase (POD) and phenylalanine ammonia lyase (PAL) on the root of the banana seedlings were measured. Then, the seedlings were inoculated by R. syzygii subsp. celebesensis. The plant growth and incidence of blood diseases were observed daily and the 31 st day after the application of LS and this bacteria inoculation. The results showed that the CS-LS, P-LS, and OPB-LS at all tested concentration could suppress the incidence of blood diseases up to 100 %, induce resistance of banana seedlings to the R. syzygii subsp. celebesensis with increased levels of ethylene, auxin, lignin, activities of POD and PAL, and plant growth, significantly. Based on the effectiveness of this bacterial control and the ability to promote the growth of banana seedlings test, it is recommended that the most effective treatment is P-LS 0.5 %.

Penyakit moler yang disebabkan oleh Fusarium oxysporum f. sp. cepae merupakan salah satu penyakit penting pada tanaman bawang merah. Aktinomiset memiliki potensi sebagai agens pengendali hayati F. oxysporum f. sp. cepae karena kemampuannya dalam memproduksi senyawa bioaktif. Penelitian ini bertujuan mengevaluasi dan menyeleksi isolat-isolat aktinomiset yang dapat menekan pertumbuhan F. oxysporum f. sp. cepae dan memacu pertumbuhan tanaman bawang merah. Penelitian dibagi menjadi empat tahap, yaitu: isolasi, seleksi, karakterisasi, dan identifikasi isolat aktinomiset yang potensial. Sebanyak 43 isolat berhasil diisolasi dari tanaman Liliaceae dan sebanyak 14 isolat berhasil diseleksi berdasarkan hasil uji keamanan hayati. Hasil uji antagonisme menunjukkan bahwa 14 isolat menghasilkan penghambatan terhadap F. oxysporum f. sp. cepae sebesar 3.67%–53.67%. Di antara 14 isolat tersebut, sebanyak 13 isolat mampu memproduksi enzim kitinase dengan indeks kitinolitik sebesar 0.31–1.38. Lima isolat terpilih yaitu: ABF42, ABF59, ACF45, AEF35, dan AEF45, mampu melarutkan fosfat dan memproduksi IAA dengan konsentrasi 24.82–82.88 ppm, namun hanya tiga isolat yang mampu memfiksasi nitrogen. Berdasarkan sikuen gen 16S rRNA, lima isolat tersebut berturut-turut teridentifikasi sebagai: Streptomyces rameus, S. lydicus, S. panaciradicis, S. seoulensis, dan S. fuscichromogenes.