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.

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Mandarin orange is economically one of the most important fruit crops in Bhutan. However, in recent years, orange productivity has dropped due to severe infection of citrus tristeza virus (CTV) associated with the gradual decline of citrus orchards. Although the disease incidence has been reported, very limited information is available on genetic variability among the Bhutanese CTV variants. This study used reverse transcription PCR (RT-PCR) to detect CTV in collected field samples and recorded disease incidence up to 71.11% in Bhutan’s prominent citrus-growing regions. To elucidate the extent of genetic variabilities among the Bhutanese CTV variants, we targeted four independent genomic regions (5′ORF1a, p25, p23, and p18) and analyzed a total of 64 collected isolates. These genomic regions were amplified and sequenced for further comparative bioinformatics analysis. Comprehensive phylogenetic reconstructions of the GenBank deposited sequences, including the corresponding genomic locations from 53 whole-genome sequences, revealed unexpected and rich diversity among Bhutanese CTV variants. A resistant-breaking (RB) variant was also identified for the first time from the Asian subcontinent. Our analyses unambiguously identified five (T36, T3, T68, VT, and HA16-5) major, well-recognized CTV strains. Bhutanese CTV variants form two additional newly identified distinct clades with higher confidence, B1 and B2, named after Bhutan. The origin of each of these nine clades can be traced back to their root in the north-eastern region of India and Bhutan. Together, our study established a definitive framework for categorizing global CTV variants into their distinctive clades and provided novel insights into multiple genomic region-based genetic diversity assessments, including their pathogenicity status.

Fasciolosis caused by Fasciola spp. is recognized to be one of the major problems affecting health and productivity of cattle in Bhutan. Various anthelmintic drugs are used to treat and control fascioliasis in the country among which, triclabendazole and oxyclozanide are the most common ones. These drugs have been used for a very long time in the country and possibility of development of resistance to these drugs is high. Also, limited studies had been carried out to test their efficacies in the country. Therefore, this study was done to determine the prevalence of fasciolosis in cattle in Maedwang gewog under Thimphu Dzongkhag and assess the status of resistance of Fasciola spp. to Fasinash® and Flunil-L® drugs. A total of 218 faecal samples were collected from cattle and subjected to parasitological test using standard sedimentation technique. The animals positive to Fasciola were treated with Fasinash® (triclabendazole bolus) and Flunil-L® (oxyclozanide+levamisole suspension). The faecal eggs were analyzed 14 days after the treatment by Faecal Egg Count Reduction Test and the efficacy was calculated. The overall prevalence of fasciolosis in the study was 32.11% with a prevalence of 28.80% in Namseling and 36.56% in Khasadrapchu. The mean faecal egg count (epg) of Fasciola spp. detected in Namseling was 0.65 ± 1.53 SD and in Khasadrapchu was 1.03 ± 2.07 SD. There was no significant difference in the mean faecal egg counts in the two chiwogs (p > .05 at 95% confidence level). The overall efficacy of Fasinash® was 86.96% and for Flunil-L ® was 91.38%. Significant difference was observed between pre-treatment and post-treatment in both the treatment groups (p < .05 at 95% confidence level). However, the study implies development of resistance of Fasciola spp. to triclabendazole in the study area.

The study assessed the accuracies of globally available Digital Elevation Models (DEM’s) i.e., SRTM v3, ASTER GDEM v2 and ALOS PALSAR DEM with respect to Topo-DEM derived from topographic map of 5m contour interval. 100 ground control points of the elevation data were collected with the help of kinematic hand held GNSS (Global Navigation Satellite System), randomly distributed over the study area. The widely used RMSE statistic, NCC correlation and sub-pixel-based approach were applied to evaluate the erroneous, correlation, horizontal and vertical displacement in terms of pixels for the individual Digital Elevation Model. Following these evaluations, SRTM DEM was found to be highly accurate in terms of RMSE and displacement compared to other DEMs. This study is intended to provide the researchers, GIS specialists and the government agencies dealing with remote sensing and GIS, a basic clue on accuracy of the DEMs so that the best model can be selected for application on various purposes of the similar region.