Incidence and Detection of Citrus tristeza virus Infecting Citrus in West Java

Abstract

Citrus is one of the economically important horticultural commodities in Indonesia, but its national production is still not optimal. Tristeza disease caused by Citrus tristeza virus (genus Closterovirus family Closteroviridae) is an important disease in citrus plants and has the potential to cause significant yield losses. This study was conducted to identify and determine the spread of tristeza disease in several citrus-growing areas in West Java Province. The study began with field surveys to citrus farms in four regencies, i.e. Bogor, Bandung, West Bandung, and Garut. Chlorosis symptoms on the farm were observed to determine disease intensity. Samples were then collected from symptomatic and asymptomatic leaves for serological detection by double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) method. Further confirmation through molecular detection was carried out by one-step reverse transcription polymerase chain reaction (one-step RT-PCR) method using CTV-specific primers, i.e. RBP 23-F/RBP 23-R. Field observations showed the variations in citrus cropping conditions and varieties at each observation site. Specific symptoms of CTV infection found involved vein clearing and chlorotic spot, leaf cupping, vein corking, and chlorosis. Disease intensity in the field was classified as moderate to very severe. DAS-ELISA and RT-PCR detection confirmed the distribution of the virus in citrus growing centers in West Java except at KJ Dayat Farm in Bandung. Nucleotide sequence analysis showed that CTV isolates from West Java consist of four virus variants, namely T68, VT, HA16-5, and T30. Further research is needed to determine the distribution area of each variant in Indonesia.

Jeruk merupakan komoditas hortikultura penting secara ekonomi di Indonesia, namun produksi nasional masih belum optimal. Penyakit tristeza yang disebabkan oleh Citrus tristeza virus (genus Closterovirus famili Closteroviridae) merupakan salah satu penyakit penting pada tanaman jeruk dan berpotensi menyebabkan kehilangan hasil yang besar. Penelitian ini dilakukan untuk mengidentifikasi dan mengetahui penyebaran penyakit tristeza di beberapa daerah penanaman jeruk di Provinsi Jawa Barat. Penelitian diawali dengan survei pengambilan sampel tanaman jeruk di empat kabupaten, yaitu Bogor, Bandung, Bandung Barat, dan Garut. Gejala klorosis di lapangan diamati untuk menentukan intensitas penyakit. Sampel kemudian dikumpulkan dari daun yang bergejala dan tidak bergejala untuk deteksi virus secara serologi menggunakan metode double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). Konfirmasi lebih lanjut menggunakan deteksi molekuler dengan metode one-step reverse transcription polymerase chain reaction (one-step RT-PCR) menggunakan primer spesifik CTV, yaitu RBP 23-F/RBP 23-R. Pengamatan di lapangan menunjukkan adanya variasi kondisi pertanaman dan varietas jeruk. Gejala spesifik infeksi CTV menunjukkan vein clearing dan chlorotic spot, leaf cupping, vein corking dan klorosis. Intensitas penyakit di lapangan tergolong sedang hingga sangat berat. Deteksi dengan DAS-ELISA dan RT-PCR menunjukkan terdapat infeksi CTV di seluruh lokasi pengamatan kecuali di Kebun KJ Dayat asal Bandung. Analisis sekuen nukleotida menunjukkan bahwa isolat CTV asal Jawa Barat memiliki empat varian virus yaitu T68, VT, HA16-5, dan T30. Perlu penelitian lebih lanjut untuk mengetahui daerah sebar masing-masing varian di Indonesia.