Detection of Root (Wilt) Disease of Coconut (Cocos nucifera L.) based on polyacrylamide gel electrophoresis

Abstract

Root (wilt) disease (RWD), caused by phytoplasma, is a major problem causing decreased coconut productivity in southern districts of Kerala and its bordering districts of Tamil Nadu in India.  The disease is non-curable but its incidence can be reduced by propagating seedlings from nuts of disease free palms. The disease free palms are selected by ELISA test which uses antiserum obtained from rabbits against  purified phytoplasma extract containing 29, 28 and 18.5 K Da proteins.   With an objective of developing a simpler  and easier biochemical test than ELISA for RWD detection in coconut , direct SDS PAGE profiles of  soluble proteins from crude leaf extracts of healthy and diseased palms of West Coast Tall (susceptible) ,  Chowghat Green Dwarf and Malayan Green Dwarf (high degree resistant) cultivars were evaluated for differences in intensities of  protein bands with molecular masses corresponding closest to the purified phytoplasma extract proteins. It was found that the 31.2, 37.3, 16.9 and 13.8 KDa bands in WCT cultivar, 31 and 40.6 KDa in CGD cultivar and 29.9 and 37.1 KDa bands in the MGD cultivar showed consistent differences in intensities and/or presence or absence of certain bands between healthy and diseased palms.  Correlations and path analysis relationship between intensity of different protein bands and ELISA value also showed significant association of one or two of these marker bands with ELISA values in each cultivar.  The SDS PAGE profiles of crude leaf extracts could be used to effectively distinguish healthy and diseased RWD palms in these three cultivars.