Prevalence of Citrus tristeza virus in Mandarin of Sikkim Himalayan Region

Abstract

The assessment of Citrus tristeza virus incidence in mandarin of Sikkim, involving sampling techniques, was estimated by DAS-ELISA. Mandarin orchards had high CTV incidence (46.32%), however, differential prevalence with regard to age of plant and location was observed. The CTV prevalence was relatively high in older orchards (51.01%) than that of younger ones (40.80%). Under all the plant age groups, south district had the highest CTV incidence (52.50%) and east district had the lowest (37.71%). The spatial distribution of CTV in plants indicates high concentration in twig followed by leaf tissue, however, stem had relatively less concentration. High aphid infestation was observed in all mandarin growing groves with the maximum in south district and minimum in east district. Taxoptera citricida was the predominating aphid species followed by T. aurantii, however, Aphis spp population was significantly less. Aphid infestation and CTV prevalence were positively and significantly correlated.Keywords Citrus tristeza virus Á DAS-ELISA Á Taxoptera citricida Citrus tristeza virus (CTV) is the most widely spread and economically important viral disease of the world [1]. It is probably originated in Asia and has been disseminated to almost all citrus-growing countries mainly by the movement of infected plant material and subsequent spread by aphid vectors with Toxoptera citricida, commonly called the brown citrus aphid, being the most efficient [13]. CTV is a phloem-limited 2000 nm long filamentous virus having single stranded RNA genome [11]. The virus is genetically and biologically diverse and can cause field symptoms ranging from vein clearing, stem pitting, yellowing, slow decline and quick decline, or no symptoms depending on virus isolate, time of infection, rootstocks, citrus cultivars and environmental conditions [4].The classical identification procedure for CTV is to graft-inoculate indicator plant of Citrus aurantifolia (Mexican lime) and observe them for vein clearing, stem pitting and leaf cupping [17] which is relatively less reliable and time consuming, but Double antibody sandwich ELISA (DAS-ELISA) [3,7,8], has revolutionized the detection test, making it feasible to test large number of samples. In recent years, PCR based diagnosis [6,10] has been used for the rapid diagnosis of citrus virus.The citrus industry of Sikkim Himalayan region is dominated by mandarin (Citrus reticulata Blanco), which is cultivated under the humid temperate climate. The region has good potential of mandarin due to climatic suitability, however, high prevalence of CTV affecting industry considerably [14]. Moreover, use of uncertified planting materials further contributes significantly to the retrogression of production potential of mandarin in Sikkim [15].Keeping in view the importance of disease-free, quality planting materials in improving the production potential of mandarin, DAS-ELISA tool was used to work out the prevalence of CTV in the major mandarin growing belts of Sikkim and in addition the infestation of ...

Citrus tristeza Virus Variants and their Distribution in Mandarin Orchards in Northeastern Himalayan Hill Region of India

“…The data in the present study revealed that CTV incidence is 48-53.3% in the Darjeeling hills and 40-60% in Sikkim hills. Thus, the previous (Biswas, 2008;Biswas et al, 2014;Kishore et al, 2010) and the present studies show that incidence of CTV is very high in Northeastern Himalayan region of India. In these regions, prevalence of aphid vector (T. citricida) is very much common (Biswas et al, 2008.…”

“…CTV is a major problem in the Darjeeling hills causing decline of mandarin orchards which are being wiping out (Biswas, 2008;Biswas et al, 2012a;Tarafdar et al, 2013, Biswas et al, 2014. Occurrence of CTV in mandarin orchards in Sikkim State has also been reported earlier (Kishore et al, 2010) but till to date, no CTV isolates from this State has been characterized genetically. Several CTV isolates of the Darjeeling hills have been genetically characterized and occurrence of 4-5 CTV variants in this hill regions are reported (Biswas et al, 2012b).…”

“…CTV incidence as high as 48.2% in the Darjeeling hills (Biswas, 2008;Biswas et al, 2014) and 46.2% in Sikkim hills (Kishore et al, 2010) has been reported earlier. The data in the present study revealed that CTV incidence is 48-53.3% in the Darjeeling hills and 40-60% in Sikkim hills.…”

High incidence of citrus tristeza virus in mandarin (Citrus reticulata) in North-East states of India

“…In this part of India Khasi mandarin have got less attention towards the infecting viruses and very limited information as well as experimental data is available for the incidence and spread of these viruses. Only three reports for CTV in Khasi Mandarin out of which one from Sikkim [16] and two reports from Assam and Meghalaya [4,6] for the entire northeast region of India which are not sufficient for the true representation of viral incidence of CTV for whole North Eastern states of India.…”

“…Moreover, biodiagnosis is not suitable for survey because the sample size during survey is usually very large and almost impossible to handle with this method. On the other hand, the protein based enzyme linked immuno-sorbent assay (ELISA) using pathogen specific polyclonal antibodies has revolutionized the detection test, making it feasible to test large number of samples [7,16]. Now a days, nucleic acid based detection by PCR/RT-PCR techniques are being used for the reliable and rapid diagnosis of citrus virus [4,9].…”