Expression and the antigenicity of recombinant coat proteins of tungro viruses expressed in Escherichia coli

Rice tungro disease (RTD) is a recurring disease affecting rice farming especially in the South and Southeast Asia. The disease is commonly diagnosed by visual observation of the symptoms on diseased plants in paddy fields and by polymerase chain reaction (PCR). However, visual observation is unreliable and PCR can be costly. High-throughput as well as relatively cheap detection methods are important for RTD management for screening large number of samples. Due to this, detection by serological assays such as immunoblotting assays and enzyme-linked immunosorbent assay are preferred. However, these serological assays are limited by lack of continuous supply of antibodies as reagents due to the difficulty in preparing sufficient purified virions as antigens. This study aimed to generate and evaluate the reactivity of the recombinant coat proteins of Rice tungro bacilliform virus (RTBV) and Rice tungro spherical virus (RTSV) as alternative antigens to generate antibodies. The genes encoding the coat proteins of both viruses, RTBV (CP), and RTSV (CP1, CP2 and CP3) were cloned and expressed as recombinant fusion proteins in Escherichia coli. All of the recombinant fusion proteins, with the exception of the recombinant fusion protein of the CP2 of RTSV, were reactive against our in-house anti-tungro rabbit serum. In conclusion, our study showed the potential use of the recombinant fusion coat proteins of the tungro viruses as alternative antigens for production of antibodies for diagnostic purposes

First report of Erwinia psidii associated with papaya dieback disease in Malaysia

Aims: The outbreak of papaya dieback disease in Malaysia has been reported since 2003. Several reports previously confirmed Erwinia papayae and E. mallotivora to be the causal pathogen of the disease. The present study aimed to identify the causal pathogen of papaya dieback disease in Sabah. Methodology and results: Infected tissues of papaya dieback disease were collected from Kota Belud, Sabah and the bacterium responsible for the infection was isolated on Luria Bertani (LB) agar and nutrient agar (NA). Seven isolates with similar characteristics to Erwinia were isolated, subjected to the Koch’s Postulates test and then identified using 16S rRNA sequencing technique. The bacterium was identified to be E. psidii, a common pathogen to guava but not to papaya. Conclusion, Significance and Impact of study: This report serves as the first confirmation of the E. psidii in causing papaya dieback disease, suggesting the possibility of this bacterium undergoing host shifting to papaya plants and the possibility of becoming another major threat to the papaya industry in the future

Screening of pea (Pisum sativum L.) resistant to powdery mildew disease for Kundasang Highland in Sabah

Pea (Pisum sativum L.) cultivation in Sabah is affected by powdery mildew caused by Erysiphe pisi DC. Fungicide application is the most preferred method of disease control by the growers. However, the non-judicious use of fungicides has led to excessive pesticide residues in the vegetable. Therefore planting of resistant variety is the best option because it is safe, cost effective and practical. Screening of the powdery mildew resistant pea variety was carried out in this study. A total of seven pea varieties were assessed for their response to powdery mildew infection at Agriculture Research Station Mesilou, Kundasang, Ranau. Their plant characters and field performances were also evaluated. Variety S7 was found to be resistant with 0 DSI score in all of the three trials conducted, the rest of the varieties were susceptible with DSI scores of 4.17 - 5.90. Marker linked to the resistance to powdery mildew was identified at about 600bp using PCR-RAPD primer 5'-ATT AGT AGT TGT TGT TG-3'. This band was found in resistant variety (S7) but absent in the susceptible varieties. The powdery mildew resistant pea identified in this study not only has the potential use in the production of resistant cultivars, but the resistant gene once identified and further characterised, can be utilised in the improvement of leguminous plants

Development of an Indirect ELISA and Dot-Blot Assay for Serological Detection of Rice Tungro Disease

Rice tungro disease (RTD) is one of the most destructive diseases of rice in South and Southeast Asia. RTD is routinely detected based on visual observation of the plant. However, it is not always easy to identify the disease in the field as it is often confused with other diseases or physiological disorders. Here we report the development of two serological based assays for ease of detection of RTD. In this study we had developed and optimized an indirect ELISA and dot-blot assay for detection of RTD. The efficiency of both assays was evaluated by comparing the specificity and sensitivity of the assays to PCR assay using established primer sets.The indirect ELISA showed 97.5% and 96.6%, while the dot-blot assay showed 97.5% and 86.4% sensitivity and specificity, respectively, when compared to established PCR method. The high sensitivity and specificity of the two assays merit the use of both assays as alternative methods to diagnose RTD. Furthermore, the dot-blot assay is a simple, robust, and rapid diagnostic assay that is suitable for field test for it does not require any specialized equipment.This is a great advantage for diagnosing RTD in paddy fields, especially in the rural areas