Weligama Coconut Leaf Wilt Disease (WCLWD) causing phytoplasma

Abstract

Coconut is one of the most important plantation crops in Sri Lanka, providing livelihood for nearly 0.5 million people (Ministry of plantation industries, 2008). Sri Lanka has earned about $ 120 million of export revenue by exporting coconut products. The Weligama Coconut Leaf Wilt Disease (WCLWD), the major threat to the crop was first reported in Weligama area in 2006. The disease has so far affected trees in the Galle, Matara, and Hambanthota districts. Although non-lethal, this disease could result in permanent injuries to the plant reducing its productivity. There would be dire consequences if this disease spreads to the coconut triangle, which includes an area of more than 70% of the total coconut cultivated land in the country. The early symptoms of the disease are difficult to be identified and also symptom development is very slow (Sasikala et al, 2005). As no reliable therapeutic agent is yet discovered for this phytoplasmic disease, the only prevention method is to remove and dispose of all affected individual trees. Up to now, the Coconut Research Institute was compelled to cut down and destroy nearly 100,000 coconut palms in the Matara district due to this disease. Phytoplasma disease diagnosis is difficult due to the inability of phytoplasma cultivation in pure cultures in vitro, their low concentration and uneven distribution in the host plant (Fránová et al., 2007). A sensitive, specific and rapid diagnostic test would be highly desirable for routine detection, mainly to avoid using infected planting material (Heinrich et al., 2001). A serological diagnostic technique based on monoclonal antibodies to the phytoplasma would provide an excellent diagnostic tool. Thus, this research aims to raise diagnostic monoclonal antibodies to WCLW phytoplasma, where initially polyclonal serum raised in experimental animals to purified phytoplasma was used to establish a specific ELISA for subsequent screening of specific hybridomas. Attempts to validate the in house established WCLWD phytoplasma specific indirect ELISA (Kanatiwela et al., 2012), using 110 coconut palms including 80 disease positive and 30 disease negative palms is reported.