Detection of Weligama Coconut Leaf Wilt Disease Phytoplasma by Real-Time Polymerase Chain Reaction

Abstract

Weligama Coconut Leaf Wilt Disease (WCLWD) is a non-lethal, but debilitating phytoplasma disease found in coconut palms in Sri Lanka which is confined to the Southern Province of the country, well-away from the major coconut growing area. If it spreads to the major coconut growing area, it might severely damage the coconut industry in Sri Lanka. Government commenced a disease control program to eradicate the disease and, more importantly to prevent spreading of the disease to major coconut growing areas. The major constraint in this program is the lack of an accurate and reliable method for identifying affected palms. Visual symptoms are used to identify the affected palms for removal, yet growers are not always convinced of the method of resisting palm removal. This poses a serious threat to the implementation of the disease control program. Although a Nested-PCR-based disease diagnosis was established earlier, the detection rate and reliability need further improvements. Therefore, an urgent necessity for a more reliable disease detection method has arisen. In the current study, a Real-Time Polymerase Chain Reaction (qPCR) powered by a pair of primers and a probe designed from the published partial sequences of the WCLWD phytoplasma was validated with 202 coconut samples and a detection rate of above 95% was achieved. This newly established detection system was highly reliable and a way forward for controlling the WCLWD disease in Sri Lanka.

Global Scenario on Phytoplasmal Diseases in Palms

“…Real-time PCR assays using 16S rDNA-based TaqMan primer-probe have been standardized for sensitive, quantitative and rapid detection of LY (Cordova et al, 2014), WCLWD (Wijesekara et al, 2020) and CYD (Nejat et al, 2010) of coconut and YLD of arecanut (Nair et al, 2014). Myrie et al (2011) developed a multiplex direct-PCR system and real-time…”

Nested PCR-Based Rapid Detection of Phytoplasma Leaf Wilt Disease of Coconut in Sri Lanka and Systemic Movement of the Pathogen

“…This could be due to the lower specificity of the primers, uneven titer and the erratic distribution of the pathogen in the plant, variability in primer-binding sites, or the association of other fastidious prokaryotes with the symptomatic samples. Even though immunological detection methods [ 16 ] and a qPCR method [ 17 ] have been developed, they are not cost-effective and feasible for large-scale studies. Therefore, further improvements to the PCR-based method are required.…”