KERAGAMAN VIRULENSI DAN MOLEKULAR VIRUS TUNGRO

R. HERU PRAPTANA, S.P., Prof. Dr. Ir. YB. Sumardiyono

2012 | Disertasi | S3 Fitopatologi

Tungro merupakan salah satu penyakit penting pada padi yang menjadi kendala dalam peningkatan produksi padi di Indonesia. Tungro disebabkan oleh infeksi dua virus yang berbeda yaitu Rice tungro bacilliform virus (RTBV) dan Rice tungro spherical virus (RTSV), yang keduanya hanya dapat ditularkan oleh wereng hijau terutama Nephotettix virescens (Distant) secara semipersisten. Adanya indikasi bahwa terjadi variasi virulensi virus tungro dari daerah yang berbeda dan hubungan spesifik antara ketahanan varietas dengan isolat virus tungro maka diperlukan suatu kajian tentang virulensi dan keragaman genetik virus tungro dari beberapa daerah endemis di Indonesia. Penelitian ini bertujuan untuk mendeterminasi virulensi virus tungro dari beberapa daerah endemis di Indonesia, mengkaji patogenisitas virus tungro pada beberapa varietas tahan serta mengidentifikasi keragaman molekular virus tungro. Satu varietas rentan yaitu TN1 dan sepuluh varietas tahan digunakan di dalam penelitian. Survei dan koleksi tanaman terinfeksi dilakukan di beberapa daerah endemis tungro yaitu Jabar, Jateng, DIY, Sulteng, Sulbar, Sulsel, Bali dan NTB. Penularan buatan dengan metode tabung digunakan dalam uji virulensi dan patogenisitas virus tungro. Wereng hijau hasil tangkapan dari lapangan digunakan sebagai penular. Virulensi virus tungro ditentukan berdasarkan nilai indeks penyakit (DI). Patogenisitas virus tungro diidentifikasi berdasarkan nilai insidensi tungro. Analisis PCR digunakan untuk deteksi keberadaan virus tungro pada tanaman terinfeksi di lapangan dan tanaman TN1 hasil penularan. Identifikasi keragaman molekular virus tungro dilakukan dengan analisis PCR-RFLP dan PCR-sequencing. Keragaman molekular virus tungro diidentifikasi berdasarkan pola potongan pita DNA serta variasi sekuen nukleotida dan asam amino dalam bentuk dendrogram kekerabatan. Hasil survei menunjukkan bahwa tungro ditemukan di semua daerah endemis dengan insidensi, sebaran dan visual keparahan gejala yang berbeda-beda. Virulensi virus tungro bervariasi di antara daerah endemis. Isolat Jateng merupakan isolat paling virulen dan tidak semua isolat dari daerah endemis di pulau Jawa lebih virulen dibanding isolat dari luar Jawa. Patogenisitas virus tungro dari beberapa daerah endemis bervariasi pada beberapa varietas tahan. Isolat Jateng, Sulteng dan NTB mampu menginfeksi semua varietas tahan dan patogenisitas isolat Jateng paling tinggi dibanding isolat yang lain. Keberadaan RTBV dan RTSV terdeteksi dalam setiap sampel tanaman terinfeksi di lapangan dan tanaman TN1 hasil penularan. Virus tungro dari beberapa daerah endemis di Indonesia teridentifikasi beragam pada tingkat molekular. Keragaman molekular virus tungro tidak berkorelasi dengan perbedaan geografi daerah endemis dan virulensi. Keragaman molekular kelompok isolat virus tungro dari Indonesia berbeda dengan kelompok dari luar negeri.

Tungro is one of the major diseases in rice which has become a constraint in increasing rice production in Indonesia. Tungro is caused by infection with two different viruses of Rice tungro bacilliform virus (RTBV) and Rice tungro spherical virus (RTSV), both of which can only be transmitted by green leafhoppers especially Nephotettix virescens (Distant) in a semipersistent manner. Since there is an indication of the existance of virulence variation of tungro viruses from different areas and the specific relationship between resistance of varieties and tungro viruses isolates, it is important to study of the virulence and the genetic diversity of tungro viruses from some endemic areas in Indonesia. This study aimed to identify the virulence and the molecular diversity of tungro viruses from several endemic areas in Indonesia as well as the pathogenicity of tungro viruses in some resistant varieties. One susceptible variety i.e. TN1 and ten resistant varieties were used in the study. Surveys and collection of infected plants and green leafhoppers were done in several tungro endemic areas, namely West Java, Central Java, Yogyakarta, Central Sulawesi, West Sulawesi, South Sulawesi, Bali and West Nusa Tenggara. Artificial transmission using the test tube method was used in the virulence and the pathogenicity test. Green leafhoppers caught from the field were used as transmitters. The virulence of tungro viruses was determined on the basis of diseases indexes (DI). The pathogenicity of tungro viruses were identified by the values of incidence of tungro. PCR analysis was used for detection of the presence of tungro viruses in infected plants in the field and the infected TN1 plants. Identification of the molecular diversity of tungro viruses was done by PCR-RFLP analysis and PCRsequencing. The molecular diversity of RTV was identified through different patterns of pieces of DNA fragments and variation in nucleotide and amino acid sequences in a phylogenetic tree. The survey results showed that tungro was found in all endemic areas with a variation in the incidence, distribution of infected clumps and visual symptomatic severity. The virulence of tungro viruses varied among endemic areas in Indonesia. The Central Java isolate was the most virulent and not all isolates from endemic areas in the island of Java were more virulent than those from outside of Java. The difference in pathogenicity of tungro viruses in some resistant varieties was observed. Isolates of Central Java, Central Sulawesi and West Nusa Tenggara were able to infect all of resistant varieties and the pathogenicity of Central Java isolate was the highest among the other isolates. The presence of RTBV and RTSV was detected in the infected plants collected from the field and the infected TN1 plants. The existence of molecular diversity of tungro viruses from several endemic areas was observed. The molecular diversity of tungro viruses was not correlated with geographic difference of endemic areas and the virulence. Tungro viruses isolates from Indonesia and those from abroad were very distinctive.

Kata Kunci : padi, tungro, RTBV, RTSV, varietas tahan, virulensi, keragaman molekular