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Mitra , S and Debnath, P and Bahadur, A and Das , SC and Kirdat, K and Yadav, A and Rao , G (2019) First Report of an Association of ‘Candidatus Phytoplasma australasia’ with Cashew nut Inflorescence Decline (CaID) Disease in Tripura, a North-Eastern State of India. Plant Diseases. , 101 (3). 970-970.

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Cashew nut (Anacardium occidentale L.), an evergreen perennial tree, is an economically important cash crop extensively used in many Indian desserts and cuisines. Cashew nuts are used for their nutritional value and are a major source of protein, fats, vitamins, oleic acid, and palmitic acid. Cashew nut cultivation is undertaken in 17 states of India covering an area of 1.04 Mha. India is the second-largest cashew nut producer in the world, producing about 817,000 MT of raw cashew nuts per annum (https://cashew.icar.gov.in). During a survey in June 2018 of cashew nut orchards in Nagicherra (latitude N 23° 48′ 37.6″; longitude E 91° 19′ 29.7″), West Tripura, India, cashew nut plants were found exhibiting deformed nuts and inflorescence decline (CaID) with prevalence of 5.6% (in a 1-ha area), which were suggestive of phytoplasma infection. Three symptomatic and asymptomatic cashew nut samples were collected, and DNA was extracted from tender shoots using CTAB. To detect the association of phytoplasma with symptomatic cashew nut samples, the isolated genomic DNA samples were assayed for amplification of 16S rRNA region using phytoplasma-specific primer pairs, namely, P1/P7 followed by nested PCR primers R16F2n/R16R2. The 16S rRNA gene of phytoplasma was detected in all collected symptomatic CaID samples, but no amplification was observed in asymptomatic samples. The obtained nested PCR fragments of ∼1.25 kb were sequenced directly (MK076296, MK729150) which showed 99.8% sequence identity with ‘Candidatus Phytoplasma australasia’, strain ‘Carica papaya’ (Y10097). The virtual restriction fragment length polymorphism analysis of 16S rRNA gene sequences delineated the CaID strain to 16SrII-D subgroup with a similarity coefficient of 1.0 using iPhyClassifier. The association of CaID phytoplasma strain with symptomatic cashew nut samples was further established by amplifying phytoplasma-specific partial secA gene (Hodgetts et al. 2008) and tuf gene (Al-Subhi et al. 2018). The phylogenetic analysis of the obtained sequences of 16S rRNA, secA (MK726365, MK726366), and tuf (MK726367, MK726368) genes confirmed the close association of CaID phytoplasma isolates with ‘Ca. P. australasia’ 16SrII-D subgroup member strains. To the best of our knowledge, this is the first report of the association of ‘Ca. P. australasia’ (16SrII-D) with inflorescence decline symptoms of cashew nut in the world. This is significant because phytoplasma strains of 16SrII-C and D have widespread host range including several fruit trees all across India (Rao et al. 2017). These strains are also known to be associated with diseases in weeds, acting as alternate hosts, spreading phytoplasmas through polyphagous insect vectors (Thorat et al. 2016). Likewise, the cashew plants are intercropped in coconut plantations and with plants like maize, groundnut, cowpea, millets, pineapple, and cassava, which are known to be susceptible to phytoplasma-related diseases, posing a threat to cashew nut plantations (Rao et al. 2017; Visalakshi et al. 2015).

Item Type: Article
Subjects: Insect Molecular Biology
Depositing User: Mr. Rameshwar Nema
Date Deposited: 31 Aug 2020 11:26
Last Modified: 02 Sep 2020 04:53
URI: http://nccs.sciencecentral.in/id/eprint/826

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