Bacteria associated with sheath browning and grain discoloration of rice in East Timor and implications for Australia’ s biosecurity Dante L. Adorada & Benjamin J. Stodart & Roni P. Tpoi & Severino S. Costa & Gavin J. Ash Received: 27 August 2012 / Accepted: 31 January 2013 # Australasian Plant Pathology Society Inc. 2013 Abstract A survey of rice growing regions in East Timor (Timor Leste) conducted in 2010 has resulted in the identifi- cation of several bacterial species associated with sheath browning and seed discolouration. Bacteria were identified by partial sequencing of the 16s rRNA gene and comparison with sequences from GenBank and EZtaxon databases. Bacterial isolates of known pathogens of rice, corn and cotton were identified, along with non-phytopathogenic endophytes. This is an indication that the disease symptoms are likely to be the result of a pathogen complex rather than caused by a single species. Unfortunately, due to current lack of infrastructure in East Timor, definitive pathogenicity testing of these isolates could not be undertaken. However, it is imperative to increase the capacity of East Timorese to improve their diagnostic skills and management of diseases of rice, and ultimately increase productivity. Furthermore, it is important to heighten the awareness of East Timorese farmers of the importance of diseases in rice production. Evidently, there is a potential source of high risk bacterial pathogens in the rice production system in East Timor and this also poses a risk to Australia’ s biosecurity. Potentially devastating pests and diseases of Australian agriculture currently present in Asia could spread into Australia via East Timor. There are a number of econom- ically important diseases of rice that occur in Southeast Asia which do not currently occur in Australia. Keywords Rice pathogen . Endophyte . 16s rRNA . Disease diagnosis Maize and rice are the main staple foods in East Timor, with an estimated production area of 38,000 ha for rice and 120,000 ha for maize (Worldmark Encyclopedia of Nations 2007). Yield per hectare of rice is approximately 1.5 mt ha, which is low compared to other rice-growing countries in Asia. This can be attributed to poor or non-application of improved varieties, quality seeds, and fertilizer. The lack of managed irrigation also has direct consequences on the number of cropping cycles that can be achieved each year. A further impediment to the yield of rice is the incidence of pests and diseases and the associated lack of crop protection strategies. In 2006, a survey of rice diseases in East Timor was undertaken to ascertain the level of risk posed by the diseases to the Australian rice industry (EH Graham Centre 2006). It highlighted the impor- tance of diseases to rice production in East Timor and height- ened the awareness of its local farmers and advisors. The survey also examined East Timorese rice production and key facilities for quarantine and plant disease research. In 2010, rice plant samples displaying sheath browning and grain dis- coloration were collected from the rice growing regions of East Timor and assessed for the presence of bacteria commonly associated with the disease symptoms. Rice crops within the villages of Dili, Aileu and Bobonaro Districts (Fig. 1) were visually inspected for sheath browning symptoms and seed discolouration. Symptoms on glumes ranged from necrotic spotting to complete discoloration (Fig. 2). Leaf-sheath lesions were light brown to black, gen- erally irregular in shape resulting in a mottling effect. During the field survey, diseased samples were kept in plastic bags with wet paper towels to provide moisture. In the laboratory, diseased tissues and seeds were surface sterilized in 70 % isopropyl alcohol for 1 min followed by three consecutive rinses with sterile distilled water (SDW) for 1 min each, D. L. Adorada (*) : B. J. Stodart : G. J. Ash EH Graham Centre for Agricultural Innovations (an alliance between Charles Sturt University and NSW DPI), Charles Sturt University, Locked Bag 588, Wagga Wagga 2678( NSW, Australia e-mail: dadorada@csu.edu.au R. P. Tpoi : S. S. Costa Ministry of Agriculture and Fisheries, Rua Nicolau Lobato No. 5, Comoro, Dili, Timor Leste Australasian Plant Dis. Notes DOI 10.1007/s13314-013-0092-z