Transmission studies on spear rot disease of oil palm

Spear rot disease (SRD) of oil palm has been consistently associated to phytoplasma presence in the phloem tissues of affected palms. This study aimed to investigate the etiological role of phytoplasmas in SRD and to explore the interrelationships between SRD, root wilt disease (RWD) in coconut and yellow leaf disease (YLD) in arecanut, all of which are known to be phytoplasma- associated diseases. Transmission studies were conducted using putative insect vectors, such as Proutista moesta and Stephanitis typica, and the vegetative vector, dodder (Cassytha filiformis), to assess the potential for cross-transmission between these diseases. The research demonstrated successful transmission of phytoplasmas from SRD-affected oil palms to healthy oil palm seedlings, healthy arecanut, and healthy coconut, as confirmed through symptom manifestation and light and electron microscopy. Additionally, transmission of RWD and YLD through these vectors was also observed, supporting the hypothesis of a shared phytoplasma association across these diseases. Phytoplasmas were identified in the salivary glands of P. moesta after prolonged acquisition and inoculation periods. These findings highlight the importance of insect vectors and dodder in facilitating the spread of phytoplasmas across different palm species. The results also underscore the need for cautious management of oil palm cultivation in regions affected by RWD and YLD, particularly with respect to the movement of oil palm sprouts from infected areas to other regions, to prevent further spread of these devastating diseases.