Orange spotting, potassium content and vertical transmission of coconut cadang-cadang viroid variants in oil palm

Oil palm, (Elaeis guineensis Jacq.) is a golden crop for Malaysia. It was first introduced to Malaysia as an ornamental plant and has become the most important commodity crop nowadays. Generally, Malaysian oil palms were free from diseases. However, with greatly increasing acreages in oil palm plantations, certain diseases and various seedling diseases became prominent. Orange Spotting (OS) is an emerging disease that has been reported in oil palm. It is caused by Coconut cadang-cadang Viroid (CCCVd). CCCVd is the causal agent of the lethal Cadang-cadang disease of coconut in the Philippines and the variants can be detected in nucleic acid extracts of both in symptomatic and asymptomatic oil palms in Malaysia. However, the epidemiology of CCCVd variants in oil palm is poorly understood. Potassium deficiency and CCCVd variant infection induced OS. Nevertheless, the symptoms are always being misled. The purpose of this study was to identify and characterize CCCVd variants from oil palm and to discuss the severity of orange spotting disease caused by CCCVd and the level of potassium content through leaf potassium analysis. The study was carried out in three main experiments which is survey and sampling, detection of CCCVd and potassium analysis. Through survey and sampling 30% OS disease incidence was recorded and 60 samples were collected. Detection of CCCVd through molecular cloning and sequencing found 48.3% samples contained CCCVd variants and five new CCCVd variants were characterized (Accession no. MF579860-MF579864). This study also found that OS symptom is not depending on or related directly to the level of potassium in oil palm leaves. The research was extended to determine vertical transmission of CCCVd variants through seeds. This objective was done through embryo culture technique and germinated seedlings. The oil palm embryos were excised then were transplanted on Murashige and Skoog media and incubated for 60 days. The plantlet and seedling were extracted for total RNA and amplified using CCCVd specific primers. These experiments found that a CCCVd variant existed in the seed's embryo and germinated seedlings. These studies demonstrate that the germination rate for embryo and seedlings was 28.9% and 37.8% respectively and frequency of CCCVd variant transmission for embryo and seedlings was 20% and 11.1% respectively, thus confirming that CCCVd is vertically transmitted. The thesis was further investigating host and gene interaction through the last objective which is to examine the effect of CCCVd infection in host gene expression. Non-radioactive Differential Display Reverse Transcriptase Polymerase Chain Reaction (DDRT-PCR) was used to fulfill this objective. The result found that non-radioactive DDRT-PCR was a fast and simple technique that permitted detection of genes whose expression level is up-regulated as well as those that are down-regulated, however, it is not escaped from high production of false positive. The experiment found that only one band was successfully re- amplified with the same primer pairs and was identical as formin binding protein 1 from FNBP 1 protein family.

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