Current incidence of tungro disease in West Java and South Sulawesi

Rice tungro bacilliform virus (RTBV) and Rice tungro spherical virus (RTSV) were identified as casual agents of tungro disease. In nature, both RTBV and RTSV are transmitted by an insect vector, green leafhopper ( Nephotettix virescens ), in a semi-persistent manner. Infected plants displayed typical symptoms, such as yellowing leaves and stunting. To date, tungro is still considered one of the most devastating rice diseases in Indonesia and Southeast Asia due to its infection, which causes significant yield loss. Therefore, this study aims to detect RTBV and RTSV from several locations. Field survey and sample collection were conducted in two locations in West Java Province (Bogor and Subang Regencies). Additional samples were obtained from the collection of the Forecasting Centre for Plant Pest Organisms in 2023, which originated from West Java Province (Purwakarta and Sukabumi Regencies) and South Sulawesi (Sidenreng Rappang Regency). Disease incidence of tungro disease varied among the regions, i.e., 5% in Purwakarta and Sukabumi, 81% in Subang, 62% in Bogor, and 40% in Sidenreng Rappang. The distribution of the disease depends on the presence of its vector. Molecular detection was done by PCR using specific primer pairs of RTBV (RTBV ORF2-F/ RTBV ORF2-R) and RT-PCR for RTSV (RTSV-F2/ RTSV-R2). All the samples tested positive for both RTBV and RTSV at 430 bp and 787 bp in size, respectively. Genetic variation based on nucleotide sequence analysis indicates the presence of strain variation among isolates. Both RTBV and RTSV samples belong to the Southeast Asian group and are separated from the South Asian group cluster. Further epidemiological research is needed to anticipate the outbreak of tungro disease in Indonesia.