Citrus, mainly mandarin (Citrus reticulata Blanco) is an economically important fruit crop in Bhutan. Despite having favorable agro-climatic conditions for citrus cultivation, the early decline of fruit-bearing orchards coupled with low crop productivity is a major concern among the citrus growers. During the recent survey, an association of ‘Candidatus Liberibacter asiaticus’ (citrus greening) and citrus tristeza virus (CTV), either singly or as mixed infection in declined citrus trees was recorded in all four major citrus-growing districts viz. Tsirang, Dagana, Zhemgang and Sarpang. Using PCR-based diagnosis, a higher incidence of citrus greening (27.45 %) and tristeza (70.58 %) was observed in symptomatic field samples. Detection and characterization of ‘Ca. L. asiaticus’ (CLas) was performed based on 16S rDNA, Prophage gene, 50S ribosomal rplA-rplJ gene, and tandem repeats of CLIBASIA_01645 locus. Similarly, coat protein, p23, and p18 genes were used as genetic markers for the detection and characterization of Bhutanese CTV. The CLas isolates from Bhutan segregated into Class-II and III based on CLIBASIA_01645 locus, analogous to Indian isolates from the north-east region and Term-A based on CLIBASIA_05610 locus. CTV isolates of Bhutan were observed as closely related to VT strain, which is considered as most devastating. To the best of our knowledge, this is the first study on molecular characterization of CLas and CTV isolates and their association with citrus decline in Bhutan.
Molecular characterization of Citrus tristeza virus strains in Peninsular Malaysia
