Ralstonia solanacearum: the bacterial wilt causal agent

Ralstonia solanacearum (race 3 biovar 2) is a bacterial wilt causal agent of many plant species. Infects (potatoes Solanum tuberosum, eggplant Solanum melongena, peppers Capsicum annuum, tomatoes Lycopersicon esculentum, geraniums, Geranium carolinianum, ginger Zingiber officinale and a few weed species including bittersweet Celastrus orbiculatus, nightshade Solanum karsense and stinging nettle Urtica dioica. Ralstonia solanacearum can be infectious in the soil for years in the presence of a host. Race 3 biovar 2 is most commonly transmitted by contaminated soil, equipment, water and insect, or by transplantation of infected seeds or seedlings. Management requires use of resistance cultivars, clean and certified seed, good cultural practices, some chemicals fumigation, antagonistic microbes as a biological control like (Mycorrhizal fungi, Streptomyces sp. and Tricoderma sp.) transgenic resistant plant, cropping systems, soil amendments, integrated control, genetically engineered antagonistic and virulent mutants of R. solanacearum

A Rust Disease on Gendarussa vulgaris Nees. Caused by Puccinia thwaitesii Berk.

Gendarussa vulgaris Nees., a common medicinal herb, was found to be severely infected by a rust disease. The disease was characterised by well defined, concave or convex, purplish-gray, discoloured lesions surrounded by a wide yellow halo on the adaxial surface and corresponding convex or concave lesions on the opposite abaxial surface. Infected leaves abort prematurely. The causal agent was identified as Puccinia thwaitesii Berk. The fungus produced both uredospores and teliospores on the same pustule and is a micro cyclic (hemijorm), autoecious rust

A Rot of Detached Durian Fruits Caused by Sclerotium rolfsii

A new fruit rot of fallen durian fruits was observed in the Uiversiti Pertanian Malaysia fruit orchard in Serdang, Selangor during the fruit ripening month of October, 1988. The rot was characterized by a dense, white, fan-shaped mat of coarse my celial strands of the causal fungus growing on a water-soaked, brown necrotic patch on the fruit in contact with decaying weed vegetation on the ground. The causal organism was identified as Sclerotium rolfsii. Presence of a thick weed undergrowth and its decaying leaf debris, and warm, moist conditions were shown to be important predisposing factors conducive to the development of the rot

Genetic diversity of Xanthomonas citri subsp. Citri, causal agent of citrus canker.

A total of 25 samples of canker disease from different part of West Malaysia were isolated from three different hosts. After various diagnostic tests, the samples were identified as Xanthomonas citri subsp. citri (Xcc), and were also pathogenic to four tested citrus species. Molecular characterization using rep-PCR fingerprinting was carried out on the isolates. Cluster analysis using the combined banding patterns of ERIC and BOX-PCR clearly divided the isolates into different clusters according to their geographical origin, but not to their host species. A relatively high amount of genetic diversity was observed among isolates, as a group of isolates from a more restricted part of Malaysia separated from the rest with relatively low similarity, indicating that there might be distinct pathotypes of the bacterium present in Malaysia

PRODUCTION OF POLYCLONAL ANTIBODY TO THE COAT PROTEIN OF CITRUS TRISTEZA VIRUS IN CHICKEN EGGS

Citrus tristeza virus (CTV) is one of the most destructive diseases in many citrus growing areas of Indonesia. Effective strategies for controlling CTV depend on diagnostic procedure namely enzyme-linked immunosorbent assay (ELISA). Study aimed to purify the CTV antigen and produced its polyclonal antibody. Virion of the severe CTV isolate designated UPM/ T-002 was concentrated by polyethylene glycol (PEG) precipitation combined with low speed centrifugation. Semipurified antigen was further purified by sodium dodecyl sulphatepolyacrylamide gel electrophoresis (SDS-PAGE). The specific coat protein (CP) band of CTV with molecular weight of 25 kD was excised and eluted using elution buffer containing 0.25 M Tris-HCl pH 6.8 + 0.1% SDS, then used as antigen for injection into 6-month-old female of White Leghorn chicken. Results, showed than the specific polyclonal antibody raised against the 25-kDa CP had a titer of approximately 104, gave low background reaction with healthy plant sap and reacted specifically with CTV isolates. The reaction was equally strong for a severe, a moderate, a mild, and a symptomless isolate, suggesting a broad reaction range of this antibody toward different CTV isolates. Optimal virus titer can be obtained since virus loss during purification could be minimized and the highly purified antigen as an immunogen could be obtained by cutting out the CP band from SDS-PAGE gels. Large amount of highly titer of CTV antibody can be produced in chicken egg. The simplicity of the procedure makes it economically acceptable and technically adoptable because the antibody can be produced in basic laboratory

Bio-compartmental in vitro system for Glomus mosseae and Ralstonia solanacearum interaction.

The life cycle of arbuscular mycorrhizal fungi (AMF) is initiated by spore germination. The interaction between Glomus mosseae and Ralstonia solanacearum was achieved by following the bio-compartmental in vitro system. The system was modified to be useful for different microbes with different types of medium. Mycorrhizal fungi spores were germinated using water agar, nutrient agar and soil media, while casamino acid-peptone-glucose (CPG) media was used for R. solanacearum.all medium. All medium were mixed with different volumes of tomato and corn root exudates. The hyphal length of G. mosseae greatly affected by the exudates particularly, mycorrhizal tomato root exudates (MTRE) and mycorrhizal corn root exudates (MCRE). The growth of R. solanacearum was suppressed due to G. mosseae spores germination which can produce different volatile and non volatiles substances. The aim of this experiment was to investigate the influence of root exudates volatiles on R. solanacearum and the hyphal of G. mosseae growth under laboratory conditions using a new modified technique

The potential of endomycorrhizal fungi in controlling tomato bacterial wilt Ralstonia solanacearum under glasshouse conditions

The impact of colonization by three mycorrhizal fungi on tomato bacterial wilt caused by Ralstonia solanaceraum was investigated. Three species of arbuscular mycorrhizal fungal (AMF) were tested (Glomus mosseae, Scutellospora sp. and Gigaspora margarita). Siginificant differences in tomato growth based on plant hieght was recorded between G. mosseae (125.25 cm) and all treatments. The combination of G. mosseae and R. solanacearum resulted in significantly taller tomato plants than G. margarita + R. solanacearum and Scutelospora sp.+ R. solanacearum. Shoot fresh and dry weight was higher in G. mosseae inoculated plants. No disease symptoms were observed in the combination treatment of G. mosseae and R. solanacearum. The plants treated with Scutellospora sp. showed low incidence of infection (105, 15%) at 15 and 20 days after inoculation, respectively. The combination of G. mosseae and R. solanacearum resulted in more increase in root morphology (root tips (434.75), root length (267.00 cm), root surface area (149.31 cm2), root volume (3.77 cm3), root fresh weight (4.75 g) and root dry weight (2.5 g). The treatment of G. mosseae + R. solanacearum was different significantly when compared to G. margarita and Scutellospora sp. + R. solanacearum treatments in all parameters considered. The highest number of AMF spores was recorded in G. mosseae treatment followed by Scutellospora sp. The concentration of N, P and K in G. mosseae + R. solanacearum treatment was significantly higher (N: 1.69; P: 0.51 and K: 1.65%) compared to G. margarita (N: 1.06 ; P: 0.11 and K: 1.02%) and Scutellospora sp., treatment (N: 1.48; P: 0.44 and K: 1.47%). Generally, the current findings has provided an evedance about the ability of AMF species to control bacterial wilt causal agents with significant differences between the species used.Keywords: Bio-control, wilt disease, tomato, Glomus mossea

Morphological, pathogenic and molecular characterization of Lasiodiplodia theobromae: a causal pathogen of black rot disease on kenaf seeds in Malaysia

Kenaf (Hibiscus cannabinus) is a fibre crop grown in Malaysia as a substitute crop for tobacco. Previous study have recorded that kenaf has been infected by various genera of seed-borne pathogen include Fusarium, Synnematium, Alternaria, Colletotrichum and Botrytis. Seed-borne disease affects and actively attacks seeds and may be harmful. Lasiodiplodia theobromae is a seed-borne fungal pathogen that infects a variety of crop seeds. Studies on the isolation of seed-borne fungi on kenaf seed have revealed that L. theobromae causes black rot disease on kenaf seeds. L. theobromae was successfully isolated from kenaf seeds on an agar plate and a blotter. L. theobromae was isolated frequently from infected seeds and identified based on its cultural and morphological characteristics. The fungus sequence was analysed using molecular technique (ITS-rDNA amplification). A pathogenicity test was used to confirm that L. theobromae caused blackening of the seeds and reduced the germination against a control treatment in potato Dextrose Agar (PDA) medium. To our knowledge, this study is the first to confirm that L. theobromae is the causal agent of black rot on kenaf seed in Malaysia

Morphological characteristics and pathogenicity of Synchytrium psophocarpi (Rac.) Baumann associated with false rust on winged bean

Problem statement: Winged bean (Psophocarpus tetragonolobus L.) is an important tropical legume in countries like Malaysia due to its potential as a high protein value crop. However, bright-orange pustules observed on the veins of young leaves, stems, pods and sepals depict symptoms of false rust disease on beans. The causal agent of this disease has been found to be Synchytrium psophocarpi. Currently, there is no published literature of this or other related species in Malaysia. Thus, there is a very serious lack of knowledge on the taxonomic characterization and pathogenicity of the local fungus. Therefore, there is an important need for this microorganism to be documented. Approach: This study was reported based from samples obtained from infected winged bean plants found in the fields around the University Putra Malaysia campus in Serdang, Selangor, Malaysia. The morphological characteristics were studied using dark field and scanning electron microscope. Meanwhile, pathogenicity test was carried out using two methods which were moist chamber and on Petri dish. Results: The sporangia were spherical to ovoid in shape and approximately 20.69 μm in diameter. The average diameter for spore measured was 2.02 μm and the flagella were 10.75 μm in length. Positive disease development with false rust disease symptoms was observed in both methods of inoculation practiced. It confirmed the pathogenicity of the fungus as the causal pathogen with the appearance of clear disease symptoms. Conclusion: This research finding is the first detailed report for Synchytrium psophocarpi associated with false rust disease of winged bean in Malaysia. It described the morphology, zoospore production and pathogenicity of the causal fungal organism. This information would be very useful for the studies involving this pathogen in future