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Articles by G. Vadamalai
Total Records ( 4 ) for G. Vadamalai
  N. Nejat , K. Sijam , S.N.A. Abdullah , G. Vadamalai and M. Dickinson
 

Abstract Problem statement: Molecular methods have been used to detect phytoplasma in Malayan Red Dwarf (MRD) ecotype of coconut for the first time in Malaysia. Detect phytoplasma from coconut showing yellowing symptoms by nested PCR and Classify phytoplasma associated with disease of coconut palms, based on analysis of 16S rRNA gene operon sequences and virtual RFLP.
Approach: Twenty MRD symptomatic palms were tested. Leaf spear, inflorescence and wood shavings from trunks of coconut palms showing yellowing symptoms were harvested from Serdang located in Selangor state. PCR assays and sequence analysis were carried out.
Results: Nested PCR with primer pairs R16F2n/R16R2 and fU5/rU3 resulted in amplification of products of approximately 1.2 kb and 890 bp respectively, from 8 out of 20 MRD symptomatic palms tested. Sequence analysis of the 16S rDNA PCR products determined that the phytoplasma strain associated with Coconut Yellow Decline (CYD) in MRD ecotype belongs to the ‘Candidatus Phytoplasma cynodontis’ (16SrXIV) group of phytoplasmas. In addition, nested R16F2n/R16R2 PCR products from 6 spear leaves and 2 inflorescences from MRD palms showed high sequence similarity to the 16S rRNA gene from coconut chloroplasts, with a similar size (approximately 1.3 kb) and a further 5 R16F2n/R16R2 PCR products from MRD inflorescences showed high sequence similarities to Bacillus spp. 16S rRNA gene sequences.
Conclusion:
These results indicate that sequencing is a reliable method for the detection. Furthermore, trunk borings are the most reliable source of DNA for phytoplasma detection in coconuts using 16S rRNA gene primers, since there is less co-amplification of PCR products from other organisms when compared to spear leaves and inflorescences, nor from the spear leaves and inflorescences of MRD palms when primers fU5/rU3 were used in nested PCR.

  S. Selvaraja , S.K. Balasundram , G. Vadamalai and M.H.A. Husni
  Orange Spotting (OS) disease which is caused by Cadang-Cadang Coconut Viroid (CCCVd) is an emerging problem in oil palm. This study was aimed at quantifying the spatial variability of OS disease severity as an effort to augment the effectiveness of OS phytopathometry appraisal. A 4.2 ha study plot was established in a commercial oil palm plantation at Sungai Buloh, Selangor. A total of 587 geo-referenced trees were visually observed for OS disease symptoms. OS disease severity data were first subjected to exploratory analysis and followed by variography and interpolation analyses to assess spatial variability. The incidence OS disease in the study area was 74.3%. Measured OS disease severity ranged from 0-92.3%. The spatial structure of OS disease severity was described by an exponential model with an effective range of 29.1 m. OS disease severity exhibited a strong spatial dependence with a nugget to sill ratio of 0.15. The spatial variability map of OS disease severity revealed spatial clustering of kriged values, where 73% of the study area showed low severity (1-30%), 25% showed moderate severity (30-60%) and approximately 2% showed high severity (> 60%). This study demonstrates the utility of geo-spatial information in understanding the OS disease severity scale which could assist in site-specific disease monitoring and intervention.
  N. Nejat and G. Vadamalai
  Phytoplasmas are small bacteria with very small genomes which also have extremely low levels of the nucleotides guanine plus cytosine (G+C). They are associated with hundreds of plant diseases globally. The uneven distribution and low concentration of phytoplasmas in the phloem of infected plant, especially in woody hosts, and variations in titre according to season and plant organ are also important obstacles for efficient diagnosis. Polymerase Chain Reaction (PCR), nested PCR and real-time PCR have been employed for phytoplasma detection. PCR is the most versatile tool for detecting phytoplasmas in their plant and insect hosts. Nested PCR with a combination of different universal primers can improve the diagnosis of unknown phytoplasmas present with low titre in the symptomatic host. Universal ribosomal primers nested with group-specific primers are extremely useful when the phytoplasma to be diagnosed belongs to a well-defined taxonomic group. Real-time PCR has been shown to be an effective method of quantifying the titre of phytoplasmas within the plant. This paper also discuss phytoplasma diseases on coconut palm.
  N. Nejat , G. Vadamalai and M. Dickinson
  Spiroplasmas are helical motile filamentous, wall-less and culturable mollicutes. Thirty six spiroplasma species have been identified. Only S. citri, S. kunkelii and S. phoeniceum have been identified as plant pathogens. Spiroplasma citri, the causal agent of citrus stubborn disease, have a wide host range. S. citri infects most citrus species and cultivars and a wide range of non-rutaceous plant species. Citrus srubborn disease widely distributed in the southwestern united states of America, northern Africa and Mediterranean countries. It is naturally transmitted by phloem-feeding leafhopper vectors. S. citri can be detected by grafting to citrus indicators, culturing on artificial media, serological, DNA probes, dot-immunobinding assay, Immunocapture Polymerase Chain Reaction (I C- PCR), Polymerase Chain Reaction (PCR) and real-time PCR. There is genetic variability among isolates of S. citri.
 
 
 
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