One of the major diseases that can reduce vanilla growth and production is stem rot caused by Fusarium oxysporum f.sp. vanillae. The objective of this study is to evaluate the rhizobacteria as biocontrol agents against Fusarium oxysporum f.sp vanillae. This research consists of isolation of rhizobacteria, antagonism assays, and identification of the rhizobacteria. A total of 263 isolates were evaluated in antagonism assays. There were 250 isolates isolated from vanilla, and 13 isolates were the collection of Plant Protection Laboratory, Indonesian Spice and Medicinal Crops Research Institute. The results showed that seven rhizobacteria isolates, i.e., L34, PS4, V116, KB7, KB10, M117a, and V112, could inhibit the mycelium growth by more than 60%. Rhizobacteria isolate L35, PS4, and V112 showed the highest inhibition, i.e., 64.92%, 72.72%, 68.72%, respectively. Based on the 16S rRNA sequence, isolate L35, PS4, and V112 were identified as Burkholderia vietnamiensis, B. ambifaria, and B lata, respectively. Further studies are needed to investigate the interaction between rhizobacteria and the host plants and formulate products to evaluate their effectiveness in the fields.
ABSTRAKRigidoporus lignosus merupakan patogen penting pada tanaman karet yang mengakibatkan penyakit akar putih. Penggunaan mikrob antagonis merupakan salah satu teknik pengendalian yang direkomendasikan untuk patogen ini. Penelitian ini bertujuan memperoleh agens hayati dari dalam jaringan akar dan rizosfer tanaman karet yang berpotensi mengendalikan R. lignosus. Tahapan penelitian terdiri atas isolasi mikrob endofit dan rizosfer dari tanaman karet, uji patogenisitas, seleksi secara in vitro, pengujian secara in vivo, pengujian pelarut fosfat dan pengikat nitrogen, dan identifikasi. Sebanyak 99 isolat bakteri dan 18 isolat cendawan nonpatogen berhasil diisolasi dari akar dan rizosfer tanaman karet. Berdasarkan pengujian in vitro dan in vivo diperoleh 2 isolat bakteri dan 3 isolat cendawan yang mampu menghambat pertumbuhan R. lignosus, yaitu bakteri endofit ME8, bakteri rizosfer MR3, cendawan endofit CB8, CB6, dan CL3. Bakteri endofit ME8 mampu melarutkan fosfat dan memfiksasi nitrogen. Bakteri rizosfer MR3 hanya mampu memfiksasi nitrogen. Berdasarkan karakter morfologinya, isolat CB8 teridentifikasi sebagai hifa steril, CB6 sebagai Chaetomium sp., dan CL3 sebagai Penicillium sp. Berdasarkan perunutan gen 16S rRNA, bakteri ME8 memiliki kekerabatan dengan Bacillus siamensis B268, dan bakteri MR3 memiliki kekerabatan dengan B. amylolyquifaciens SXAU001. Mikrob endofit dan rizosfer yang telah diisolasi dari tanaman karet memiliki potensi sebagai agens hayati untuk mengendalikan R. lignosus.Kata kunci: fiksasi nitrogen, mikrob antagonis, pelarut fosfat, penyakit akar putih ABSTRACTRigidoporus lignosus is the most important pathogen of rubber tree which causes white root rot disease. The use of antagonistic microbe is recommended to control this pathogen. This research was conducted to isolate endophytic and rhizospheric microbes, and to study their ability to inhibit growth of R. lignosus. Research consisted of isolation of endophytic and rhizospheric microbes, pathogenicity test, in vitro and in vivo assays, growth promotion assays, and identification. There were 99 isolates of bacteria and 18 isolates of fungi isolated from the root and rhizosphere of rubber trees. In vitro and in vivo assay showed that 2 bacterial isolates, i.e. endophytic bacteria ME8, and rhizospheric bacteria MR3; and 3 fungal isolates, i.e. endophytic fungi CB8, CB6, and CL3 were able to inhibit the growth of R. lignosus. Endophytic bacteria ME8 showed the ability of solibilizing phosphate and fixing nitrogen. Rhizospheric bacteria MR3 showed the ability of solubilizing phosphate. The isolates CB6 and CL3 were very similar with Chaetomium sp. and Penicillium sp., respectively based on morphological characters; while CB8 was identified as mycelial sterile. Based on 16S rRNA sequences, endophytic bacterium ME8 and rhizospheric bacteria ME3 were identified as Bacillus siamensis B268 and B.
Aflatoxin contamination has become a constraint on nutmeg. The study aimed to determine the effectiveness of clove oil coating formula to suppress Aspergillus flavus growth on unshelled nutmeg. Clove oil, Curcuma oil, and coconut shell liquid smoke were evaluated for their fungicidal action on A. flavus and formulated the best one with powder carriers. The seeds were pre-treated with gelatin solution (1%) to improve coating adhesiveness, sprayed with A. flavus conidia, and incubated in humid conditions. Clove oil showed the strongest fungicidal action on A. flavus and was formulated (10%) with MgO, CaSO4, and CaO (1:1:1) powder. The coating formula could inhibit A. flavus growth, but A. flavus still colonized the seed’s inner part. The coating formula did not affect the seed’s water content, ranging from 9.8-10.22%. Pre-coating the unshelled source with gelatin solution (1%) improved the formula’s coverage on the seed surface. The coating was more resistant after mechanical impact by falling from a 30 cm high. The amount of coating formula for treating 1000 unshelled seeds (11.75 kg) was approximately 2.8 kg. The coating formula of clove oil mix with carrier powder minimized A. flavus contamination of nutmeg shells.
Coating of nutmeg seeds may prevent the colonization of Aspergillus contamination. The study aimed to evaluate the effect of coating formulas to A. flavus on shelled nutmeg. Shelled nutmeg seeds were coated with aqueous (TT) and gel (GM+) formulas containing propylparaben (0.1%), potassium sorbate (0.8%), and clove oil (1.25%), and the aqueous GM- (0.65% clove oil and 0.4% potassium sorbate). The coated seeds were then sun-dried and sprayed with A. flavus conidia. The untreated control was only inoculated with A. flavus. The colonization of A. flavus on the seeds was visually observed. The aflatoxins, propylparaben, and potassium sorbate in the treated seeds were analyzed with HPLC. The results showed that seeds treated with GM+, GM-, and TT formulas were visually free from A. flavus. The total aflatoxins were not detected in the seeds treated with the GM+, but in the coated with GM- and TT was 0.95 µg/kg and 12.6 µg/kg, respectively. In the uncoated seeds, the total aflatoxins were 695.9 µg/kg. Propylparaben and potassium sorbate residues in the coated seeds were 66-11 mg/kg and 213-415 mg/kg, respectively. The coating formula effectively minimized A. flavus colonization and aflatoxin. Therefore, the coating formula could be used for reducing Aspergillus contamination.
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