Comparative Morphology and characterization of colletotrichum isolates occurring on Cocoa in Malaysia

Isolation from cocoa leaves showing symptoms of shot-hole, blight or irregular leaf spot and from cherelles and pod rot yielded Colletotrichum gloeosporioides. No distinct differences in cultural and morphological characteristics were noted between the various isolates. The fungus was found to grow and sporulate well at 3()C. Cocoa LeafExtract Agar (CllA) was the best medium for mycelial growth while Potato Dextrose Agar appeared to favour sporulation. Both cocoa leaves and injured pods were liable to infection by C. gloeosporioides. Three week old cocoa seedlings and cherelles were noted as the most susceptible stages

Characterization of Burkholderia cepacia genomovar I as a potential biocontrol agent of Ganoderma boninense in oil palm

Burkholderia is an important bacterial genus containing several species of ecological, biotechnological and pathological interest. Bacterial isolate can be gotten from soil, water, plants and even clinics. With their taxonomy undergoing constant revision and the phenotypic similarity of several species, correct identification of Burkholderia is difficult. Burkholderia cepacia complex (Bcc) consists of nine discrete genomic species and a genetic scheme based on the recA gene has greatly enhanced the identification of B. cepacia complex species. The objectives of this study were to identify Burkholderia strain UPM B3 which was isolated from oil palm roots to the species level based on Biolog® Identification System, and to carry out DNA fingerprinting for strain differentiation as well as differentiate between pathogenic and non-pathogenic human forms. Antagonistic activity of UPM B3 against Ganoderma boninense was alsoevaluated by using dual culture and poison food tests. Genotype characterization was carried out by amplification of the recA gene using specific primers, purified using QIA Quick polymerase chain reaction (PCR) purification kit and sequenced. Multiple sequence alignments were performed on closely related sequence accessions using CLUSTAL W software. Result of nucleotide sequencing followed by phylogenetic analysis of the recA fragments differentiated both putative and known Burkholderiaspecies and all members of the B. cepacia complex. Genomovar analysis confirmed that UPM B3, isolated from oil palm roots belongs to genomovar I and has antagonistic activity against G. boninense based on in vitro dual culture and poison food tests. From the phylogenetic tree, UPM B3 is a specific strain within B. cepacia complex species that belong to genovomar I which is associated with strains nonpathogenic to humans. Thus, B. cepacia strain UPM B3 has the potential to be used against G.boninense, the causal pathogen of basal stem rot (BSR) in oil palm

Micropropagation of some Malaysian banana and plantain (Musa sp.) cultivars using male flowers

Male inflorescences have potential to be used as explants for rapid micropropagation of Musa sp. The male flowers of four banana cultivars, namely ‘Berangan’, ‘Rastali’, ‘Nangka’ and ‘Abu’ belonging to three genome types in Musa (AAA, AAB, and ABB), were cultured onto Murashige and Skoog (MS) medium which was supplemented with 1 mg/L of TDZ, BAP, Kin, 2-ip and Zea. The number of shoots was found to significantly increase in both TDZ and BAP treatments, as compared to other cytokinins.TDZ at 0.4, 0.6 and 0.8 mg/L, in particular, appeared to be optimum for shoot induction in ‘Berangan- AAA’, ‘Rastali-AAB’ and ‘Nangka-AAB’ and ‘Abu-ABB’, respectively. However, all the cultivars showed their highest response to regeneration at 8 mg/L of BAP. After the initiation of the explants onto the MS media for all the cultivars, the highest number of cauliflower-like bodies’ (CLBs) clusters was observed at two months of culture. The number of induced ‘CLBs’ cluster is dependent on the size of male buds. Male inflorescences with the size of 20 mm were found to induce more ‘CLBs’ clusters. Meanwhile, the number of shoots produced is dependent on both the cytokinins and cultivars used

Molecular identification and phylogenetic analysis of Pseudoperonospora cubensis isolates in Peninsula Malaysia

Thirteen isolates of Pseudoperonospora cubensis, the causal agent of downy mildew, were collected from cucurbit fields in five states of the western part of Peninsular Malaysia during its growing season between November 2008 and March 2009. The host range of these isolates was determined previously using leaf disc assay and the results indicated that there were 12 pathotypes among these isolates. The objective of this study was to analyze the 13 isolates for phylogenetic relationship using internal transcribed spacers (ITS) of ribosomal DNA (rDNA) and mitochondrial COX-II regions. A high sequence similarity among the 13 isolates and similar sequences from GenBank were detected in ITS (>99%) and COX-II (>98%) regions. Phylogenetic analysis of the 13 isolates based on Minimum Evolution method performed on ITS and COX-II regions revealed five and three groupings, respectively. However, no relationship was found between the phylogenetic groupings using both genes and pathotypes in this study

Effect of cold-water irrigation on bacterial wilt pathogen of tomato.

Bacterial wilt caused by Ralstonia solanacearum is one of the most devastating bacterial diseases of plants worldwide. Management of bacterial wilt in tomato and other crops has been difficult, and so novel but easily implemented control methods are being sought. To evaluate the effect of cold-water irrigation on bacterial wilt of tomato, four treatments were used in which CF (chemically fertilized) soil and CF + FYM (chemical fertilizer + farmyard manure [FYM]) soil were inoculated with a bacterial suspension (R. solanacearum strain YU1Rif43) at 106 colony forming units (CFU) g−1 soil. Tomato seedlings were grown in Agri-pots in a plant growth chamber. The soil was irrigated with water that was kept at the same temperature in each treatment: 4, 10, 20, or 30°C. Incidence and severity of wilt, counting of the colonies of the culturable population of pathogen, and dry-mass and height of the plants were examined. After 45 days and in both kinds of soil, most of the plants had wilted in soil irrigated at 30°C. Wilt incidence was substantially reduced when transplanted seedlings were irrigated at lower temperatures (4–20°C). Survival of R. solanacearum was also reduced after being irrigated with water at lower temperatures, indicating that the reduced incidence of wilt was linked to reduced survival of the pathogen. Dry-mass and plant height were slightly higher under control conditions than in soils irrigated at lower temperatures. This study suggests that cold-water irrigation could significantly reduce bacterial wilt of tomato and have an adverse effect on survival of the wilt pathogen

Pathogenicity of Colletotrichum truncatum and its influence on soybean seed quality

Pathogenicity of Colletotrichum truncatum and its influence on soybean seed quality were evaluated by artificial inoculation. C. truncatum enabled to establish as latent infection without showing any visible symptom in all seed components with maximum frequency values of 100% for seed coat, 43.0% for cotyledon and 30.0% for embryonic axes after 4 days of incubation period. The infection level remained the same in all seed components until the end of the incubation period. Fungal infection reduced seed germination by 29.2% and viability by 26.9% than un-inoculated seeds in vitro. Moreover, infection increased the electrolyte leakages compared with control. Under glasshouse conditions, pathogenicity of C. truncatum on seeds and seedlings was more virulent than that of controlled conditions. In the glass house, C. truncatum reduced seed germination and seedling survival by 46.4% and 75.8%, respectively and caused pre- and post-emergence damping-off of seedlings. However, fungal infection by C. truncatum increased protein and oleic acid content and reduced linoleic acid content, but did not change in extracted oil and other fatty acids when compared with un-inoculated seeds after 4 days of incubation

Prospects for inhibition of lignin degrading enzymes to control ganoderma white rot of oil palm

Oil palm (OP) is prone to a rot by the fungus Ganoderma which may be capable of being controlled by enzyme inhibitors. Palm oil is used in the production of vegetable oil for foods, cosmetics, pharmaceuticals and, most recently, biodiesel. However, the fundamental process of the disease as “white rot” has been ignored by researchers. White rot fungi are capable of degrading lignin ultimately to carbon dioxide and water: Celluloses become available as nutrients for the fungus. One potential control method is to inhibit the ligninolytic enzymes. There are few data on the lignin of OP and none on how it is degraded by OP Ganoderma and so specific examples on how to inhibit the enzymes of the fungus is impossible. Fortunately, there is more information on lignin and lignin model compounds degraded by other fungi. The taxonomy of Ganoderma is confused; hence drawing direct comparisons between other taxa within the genus in terms of ligninolysis is of limited utility. In general, ligninolytic enzymes can be inhibited by (a) temperature, pH and aeration, (b) high carbon and high nitrogen and (c) halides, metal chelators, heavy metals, and reducing agents. These factors require to be tested against the enzymes from Ganoderma from OPs in vitro with a view to developing control methods in the field, and this is how the area requires to be progressed. Furthermore, the procedures may be useful to control other rots of trees and wood products. In the case of OP, such compounds could be (a) injected into (b) sprayed onto and/or (c) added to the soil of the OP. In conclusion, the control of Ganoderma of OP would benefit from investigating the effect of inhibitors on the lignin degrading enzymes in vitro to enable this to be applied in plantations

Tomato yellow leaf curl virus (TYLCV) alters the phytochemical constituents in tomato fruits.

An investigation was conducted in order to evaluate the responses of field grown tomato varieties (Marglove and Roma VF) to tomato yellow leaf curl virus (TYLCV). Fruit samples from the virus-infected and uninfected plants were collected at 20 (early stage), 40 (intermediate stage) and 60 days (ripening stage) after anthesis. Results showed higher virus RNA content in fruits of infected plants at early (42.48 to 38.24%) and intermediate stages (34.35 to 19.57%). There was a substantial decrease in DNA content (27.27 and 21.05%) at early and (23.08 and 43.75%) at intermediate stages of both Marglove and Roma VF, compared to the control, respectively. Similarly, indole acetic acid content was also decreased (27.08 and 24.29%) in fruits of virus-infected Marglove and Roma VF, respectively. The free ascorbic acid content was found lower (35.29 to 51.52%), while combined ascorbic acid was higher (13.91 to 33.33%) in both varieties. Neither the responses of individual organic acids nor their concentrations in fruits of infected and control plants were identical. Fumaric acid was not detected either in fruits of infected plants of Marglove or in healthy and infected Roma VF. Individual fruit weight and fruit numbers per plant were lower in the virus-infected plants. This study indicates that the yield of infected tomato plants could be reduced by the infection of TYLCV due to the changes in the concentrations of phytochemical constituents. This suggests that monitoring and management of TYLCV incidence is crucial for yield and quality optimization of field grown tomato

PGPM-induced defense-related enzymes in aerobic rice against rice leaf blast caused by Pyricularia aryzae

Rice blast caused by Pyricularia oryzae is the most devastative disease especially under aerobic cultivation systems. The bio-efficacy of plant growth-promoting microorganisms: Pseudomonas aeruginosa (UPMP1), Corynebacterium agropyri (UPMP7), Enterobacter gergoviae (UPMP9) and Bacillus amyloliquefaciens (UPMS3), Trichoderma harzianum (UPMT1) and Trichoderma virens (UPMT2) in induction of defense-related enzymes against Pyricularia oryzae was evaluated in rice cultivated under aerobic conditions. Under dual culture plate testing, all PGPMs indicated antagonism against P. oryzae with percentage inhibition radial growth (PIRG) which ranged from 51.69–81.97 %. The bio-efficacy of the respective PGPM in induction of defense-related enzymes in rice seedlings was evaluated based on individual inoculation before challenged inoculation with P. oryzae under greenhouse conditions. Inoculation of all PGPMs significantly reduced rice leaf blast severity at day eight after P. oryzae inoculation. The reduction in rice leaf blast disease severity was associated to the increase of peroxidase (PO), polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) activities in rice seedlings when pre-inoculated with PGPMs. The highest leaf blast disease reduction (59.17 %) occurred with rice seedlings pre-inoculated with C. agropyri (UPMP9), followed by P. aeruginosa (UPMP1) (40.65 %), T. harzianum (UPMT1) (42.23 %), T. virens (UPMT2) (20.85 %), E. gergoviae (UPMP9) (17.84 %) and B. amyloliquefaciens (UPMS3). The high efficiency of PGPM in leaf blast disease suppression was associated with significant increase in total microbial activity (FDA hydrolysis) in rhizosphera soil (4.80–7.86 μg/g/0.5 h) compared to the control (2.25 μg/g/0.5 h). Thus, the application of PGPM is a potential alternative approach in rice leaf blast disease management of aerobic rice