DISTRIBUSI DAN IDENTIFIKASI BAKTERI PATOGENIK BAWANG MERAH DI BEBERAPA SENTRA PRODUKSI DI INDONESIA

ASRUL, Prof. Dr. Ir. Triwidodo Arwiyanto, M.Sc.

2015 | Tesis | S3 Fitopatologi

Penyakit bawang merah yang disebabkan oleh bakteri patogenik merupakan penyakit baru dan belum banyak dilaporkan keberadaannya di Indonesia. Di Amerika Serikat, serangan bakteri patogenik menyebabkan kehilangan hasil panen mencapai 100%. Penelitian ini bertujuan untuk (1) mengetahui dan mengkaji daerah sebaran penyakit bawang merah yang disebabkan oleh bakteri patogenik; (2) mengkaji dan mempelajari perbedaan tingkat virulensi isolat patogen dominan yang berasal dari daerah sentra produksi bawang merah yang berbeda; (3) mengkarakterisasi dan mengidentifikasi bakteri patogenik yang berasosiasi dengan bawang merah sakit berdasarkan analisis genotipik (molekular) dan fenotipik (konvensional). Penelitian ini menggunakan metode survei untuk mengetahui daerah sebaran penyakit melalui pengumpulan data sekunder, wawancara dan pengamatan lapangan berupa gejala dan tanda penyakit, intensitas penyakit, dan keberadaan patogenik dalam tanah. Identifikasi bakteri patogen dilakukan dengan metode molekular (analisis Rep-PCR, analisis DNA berdasarkan PCR-RFLP, sequencing gen 16S-rRNA dan analisis filogenetik) dan konvensional (pengamatan koloni dan sel patogenik, uji fisiologis dan biokimiawi, serta uji kisaran inang). Hasil survei menunjukkan bahwa penyakit hawar daun bakteri telah ditemukan tersebar di Desa Kalirahayu (Cirebon), Sidapurna (Tegal), Sukomoro (Nganjuk), Tirtomulyo (Bantul) dan Sidera (Sigi), sedangkan penyakit busuk umbi hanya tersebar di dua Desa, yakni Sukomoro dan Tirtomulyo. Hasil identifikasi secara konvensional berdasarkan reaksi fisiologis dan biokimiawi (fenotipik) mendekati kesamaan dengan hasil identifikasi secara molekular berdasarkan gen 16S rRNA (genotipik). Identifikasi secara molekular menunjukkan bahwa seluruh isolat asal daun, yakni CR30, CR14, CR11, NG25, TG24, PL7, BT14 dan BT29 mempunyai hubungan kekerabatan genetik lebih dekat dengan spesies P. ananatis dan menyerupai sifat-sifat biokimia dengan bakteri tersebut, sedangkan isolat asal umbi, yakni UBNG21 teridentifikasi sebagai anggota dari spesies E. cloacae. Hasil uji kisaran inang menunjukkan bahwa isolat bakteri patogen asal daun bawang merah dapat menimbulkan penyakit hawar daun bakteri pada bawang bombay (Allium cepa L), bawang daun (A. fistulosum L.), dan bawang putih (A. sativum L.) tetapi tidak menimbulkan gejala penyakit pada bawang kucai (A. tuberosum). Kata kunci: bawang merah, bakteri patogenik, Erwinia, Enterobacter, Pantoea, Xanthomonas,

Shallot diseases caused by pathogenic bacteria is a new disease and it has not been reported to exist in Indonesia. In the United States, pathogenic bacteria have caused a yield loss of up to 100%. This study aims to (1) identify and study the distribution of shallot diseases caused by pathogenic bacteria; (2) examine and study the differences in the level of virulence of the dominant pathogenic isolates derived the different production centers; (3) characterize and identify the pathogenic bacteria associated with diseased shallots according to genotypic (molecular) and phenotypic (conventional) analyses. This research used a survey method to determine the spread of the disease through secondary data collection, interviews and field observations, i.e the symptoms and signs of the disease, the intensity of the disease, and the pathogenic presence in the soil. Identification of pathogenic bacteria was carried out by using molecular methods (Rep-PCR analysis, DNA analysis based on PCR-RFLP, 16S-rRNA gene sequencing and phylogenetic analysis) and conventional methods (observation of colonies and pathogenic cells, physiological and biochemical tests, as well as a host range test). The results of the survey showed that a bacterial leaf blight was found to be dispersed in the villages of Kalirahayu (Cirebon), Sidapurna (Tegal), Sukomoro (Nganjuk), Tirtomulyo (Bantul) and Sidera (Sigi), whereas decayed tuber disease spread in only two villages, namely Sukomoro and Tirtomulyo. Pathogenic isolates originating from Cirebon, Tegal, Nganjuk, Bantul and Sigi showed no degree of virulence; there was no difference in the level of virulence but they had a high virulence against all the shallot cultivars. The results showed that conventional identification based on physiological and biochemical reactions (phenotypic) had been approach similarity with the molecular identification based on 16S rRNA gene (genotypic). The molecular identification results showed that all isolates from the leaves, i.e, CR11, CR14, CR30, TG24, NG25, PL7, BT14, and BT29 had a closer genetic relationship with a species P. ananatis and resembled the biochemical properties of these bacteria. A isolate from tubers, i.e UBNG21, was identified as a member of the species E. cloacae. The results of a host range test showed that the bacterial isolates of pathogenic bacteria from shallot leaves could cause bacterial leaf blight on onion (Allium cepa L), welsh onion (A. fistulosum L.) and garlic (A. sativum L.) but they caused no disease symptoms on garlic chives (A. tuberosum). Keywords: Erwinia, Enterobacter, Pantoea, Xanthomonas, shallot, pathogenic bacteria

Kata Kunci : bawang merah, bakteri patogenik, Erwinia, Enterobacter, Pantoea, Xanthomonas; Erwinia, Enterobacter, Pantoea, Xanthomonas, shallot, pathogenic bacteria