Assessment and molecular detection of Candidatus Liberibacter asiaticus in mandarin orange and acid lime in Tamil Nadu

Abstract

The Greening disease of citrus, popularly known as Huanglongbing (HLB), has been severe in India since late 1966. It is associated with infection by ‘Candidatus Liberibacter asiaticus,’ a heat-sensitive, non-cultured, phloem-limited alpha-proteobacterium. Leaf samples exhibiting greening symptoms were picked up from 26 Mandarin orange trees from each 5 orchards in the Dindigul district and 13 Acid lime trees from each 5 farms of Nilgiris, Dindigul and salem districts of Tamil Nadu. Among ten amplicons were derived from nine samples. Nine samples among them yielded between 1, 100-bp to 1160bp amplicon indicative of ‘Ca. L. asiaticus’ infection, the mandarin orange samples are amplified with A2 and J5 primers which showed 690bp amplicon size targeting (rplKAJL-rpoB) Beta operon gene of Las. The amplicons obtained from the samples were sequenced, and all showed approximately 1 160bp, identical to the cognate ‘Ca. L. asiaticus’ NCBI GenBank. Based on the survey results, the phylogenetic tree was built and interpreted. It has been concluded that up to date, only ‘Ca. L. asiaticus’ is the only strain associated with citrus greening (HLB) in commercial citrus Orchards of Tamil Nadu.