Screening and Characterization of Bacterial Antagonists as Potential Agents for the Biological Control of the Chrysanthemum White Rust Disease
Penapisan dan Karakterisasi Bakteri Antagonis yang Berpotensi sebagai Agens Hayati untuk Pengendalian Penyakit Karat Putih pada Krisan.
Abstract
White rust disease caused by Puccinia horiana (Basidiomycetes: Uredinales) is the major problem on chrysanthemum plantation and caused yield lost until 100%. Biocontrol is an alternative way to control this disease. Therefore, the aims of this study are to obtain antagonist bacterial as biocontrol agents of chrysanthemum white rust disease, to identify the potential isolate and their biocontrol character, charachterized their biocontrol mechanism, and to know the role of their chitinolytic activity on germination of teliospore. The methods used in this study are selection of antagonistic bacteria which are able to control this disease in-vitro, characterized of potential antagonist bacteria with polymerase chain reaction of a 16S rRNA gene and physiology and biochemical character, characterized the mechanism of inhibition teliospore germination, and the role of chitinolytic activity in antagonism activity using transposon mutagenesis. The result showed that out of 29 bacterial isolates, 12 isolates had chitinolityc activity. The twelve isolates were the potential antagonist agents to control teliospore germination with percentage above 90%. Isolate K2 was the most potential antagonist bacteria to control this disease. This isolate could inhibit the germination up to 98% and had the highest chitinolytic activity among the isolates. Based on 16S rRNA gene partial sequences analysis and physiology and biochemical characters, this isolate was identified as Chromobacterium sp. The major mechanism was antibiosis. It is showed from the biocontrol activity which are bacteria’s cell colonization, lytic activity, and disintegrated of protoplasm. This bacteria produced cyanide acid (HCN) and phenazine beside chitinolytic enzyme. Chitinolytic activity was not a single factor in the mechanism of antibiosis but other secondary metabolic compounds produced by this bacteria also come into play. It is showed on the results of mutagenesis that transconjugants which had no chitinolytic activity was still able to inhibit germination of teliospora, whereas transconjugants which still had an activity equal to or smaller than wild type bacteria, the inhibitory were lower. It was indicated that chitinase was not the most important compound that inhibited the germination of teliopsore. There was another compound have the bigger role such as hydrogen cyanide, phenazine, or other substances produced by Chromobacterium sp.. Krisan merupakan salah satu komoditas tanaman hias utama di Indonesia. Salah satu kendala dalam budidaya tanaman krisan adalah penyakit karat daun krisan yang disebabkan oleh Puccinia horiana (Basidiomycetes:Uredinales). Secara umum gejala yang ditimbulkan berupa pustul berwarna kuning oranye yang diselimuti tepung seperti karat pada permukaan bawah daun. Pustul tersebut lama-lama akan berubah putih seiring dengan perkembangannya. Infeksi dari cendawan karat bersifat lokal dan terkadang menjadi gejala sistemik. Kerusakan yang ditimbulkan dapat mencapai 100% sehingga tanaman tidak menghasikan bunga karena infeksi terjadi sejak tanaman berumur 30 hari setelah tanam. Teknik pengendalian penyakit tanaman umumnya menggunakan pestisida dan varietas tanaman yang tahan. Alasan utama penggunaan pestisida karena efeknya dapat langsung dilihat dalam waktu yang singkat, mudah didapatkan, praktis, dan dapat bersifat kuratif atau preventif. Penggunaan yang terus menerus dan tidak sesuai dengan aturan efektivitasnya dapat berkurang atau hilang karena menimbulkan resistensi pada patogen. Selain itu beberapa pestisida tidak dapat terurai sehingga dapat mencemari lingkungan. Sehingga dianggap kurang aman dan efektif. Pengendalian dengan menggunakan varietas tahan bersifat preventif. Namun dianggap kurang efektif karena sifat ketahanan tersebut dapat dipatahkan. Hal ini terjadi karena sifat virulensi dari patogen tersebut dapat cepat berubah. Oleh karena itu dibutuhkan suatu alternatif pengendalian yang efektif, efisien, dampak dari pengendaliannya dapat bertahan lama, dan ramah lingkungan. Biokontrol atau pengendalian hayati dapat dijadikan solusi.