Abstract
Weligama Coconut Leaf Wilt Disease has been reported to infect the coconut palms in Southern Sri Lanka. Intra-cellular pathogen phytoplasma has been identified as the causal organism of this disease. So far there have been no known control methods to cure diseases caused by intra-cellular pathogens. Integration of resistant varieties into management programmes has been identified as a viable option in management strategies of such diseases. For this, it is essential to identify the resistance of available genetic resources. This study was carried out in the Weligama and Matara area of Southern Sri Lanka to screen the coconut germplasm for resistance to Weligama Coconut Leaf Wilt Disease. Infected and healthy palms were differentiated using symptomatology; flaccidity of leaves, yellowing of leaves and marginal necrosis of leaflets. Sri Lanka Tall, Sri Lanka Green and yellow dwarfs, Gon thembili tall and king coconut were among the main coconut forms studied. Out of them Sri Lanka Green Dwarf recorded a high level of resistance (98%). Within the Sri Lanka Yellow dwarf and Gon thembili tall, certain individual genotypes were observed to be resistant while king coconut was identified to be susceptible. The most popular commercial coconut variety, Sri Lanka tall was highly susceptible to the disease although there were certain individual genotypes which were resistant. Although Sri Lanka Green dwarf has not so far been viable as a commercial coconut cultivar the presence of resistant genes within the coconut germplasm was recognized as a great advantage in breeding coconuts for resistance to Weligama Coconut Leaf Wilt Disease.
Highlights
Weligama Coconut Leaf Wilt Disease (WCLWD) that has been reported in Southern Sri Lanka is known to be caused by Phytoplasma (Perera et al 2012)
The coconut form Sri Lanka Green Dwarf (SLGD) was given special reference in this field survey because this particular variety has been reported to be resistant to another phytoplasma associated disease, lethal yellowing which is found in the Caribbean
Coconut varieties Sri Lanka tall (SLT) and Gon thembili tall (GTT) and several other phenotypes belonging to variety Typica, Sri Lanka Green dwarf (SLGD) (Plates 01 and 02) including Green dwarf 'Murusi' form (Ekanayake et al 2010) and Sri Lanka Yellow dwarf (SLYD) belonging to variety Nana and King coconut (KC) from Intermediate coconut variety Aurantiaca were evaluated in the survey for resistance to WCLWD
Summary
Weligama Coconut Leaf Wilt Disease (WCLWD) that has been reported in Southern Sri Lanka is known to be caused by Phytoplasma (Perera et al 2012). Home gardens on the other hand, especially in the Southern part of the island consist ofmuch diverse coconut genetic material including many of the indigenous coconut varieties and forms found in Sri Lanka. Covering the entire available coconut diversity in the area is important to identify the total pool of coconut varieties and forms which is resistant to WCLWD.
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