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 ...

Tomato is affected by the major disease late blight caused by Phytophthora infestans in Sikkim. In vitro experiment of biocontrol agents, botanicals and organically approved chemicals evaluated against P. infestans revealed that garlic, Trichoderma harzianum, copper oxychloride and copper hydroxide were effective. In field experiment conducted during 2014 and 2015, copper oxychloride @0.25% was found most effective followed by copper hydroxide @0.25% for the management of late blight. The pooled mean yield of tomato treated with copper oxychloride was recorded highest with 8.99 t/ha, 24.50 t/ha and 25.33 t/ha for open, rain shelter and tunnel, respectively followed by copper hydroxide. Hence, copper fungicides can be used for the management of late blight in tomato in organic farming.

Leaf streak caused by Pestalotiopsis royenae (Guba) Steyaert has been reported as a new disease of large cardamom (Amomum subulatum). It is characterized by rectangular spots running parallel to the veins. P. royenae was isolated onto potato dextrose agar from the infected portion of the plant. In the pathogenicity test, disease symptoms were not present on inoculated plant and on detached leaf in vitro after 20 days. During 2014-2016, a survey in various large cardamom plantations of Sikkim revealed the presence of tea mosquito bugs on the infected parts of A. subulatum. The spots did not show any growth. Different sized spots have been noticed on the infected leaf produced by different instars. At the initial stage, these symptoms appear on the young and tender leaves of large cardamom. Tea mosquito bugs were collected from the infested leaves and allowed to feed under controlled conditions, which produced similar type of leaf streak symptoms in large cardamom and also in other non-host crops like maize and turmeric.The results reveal that the cause of leaf streak is due to feeding injury of tea mosquito bugs and rule out P. royenae as a pathogen causing leaf streak disease symptoms. Pestalotiopsis sp. was also isolated as endophyte from large cardamom.

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