First Report of an Association of ‘Candidatus Phytoplasma australasia’ with Cashew Nut Inflorescence Decline in Tripura, a Northeastern State of India

Abstract

HomePlant DiseaseVol. 104, No. 3First Report of an Association of ‘Candidatus Phytoplasma australasia’ with Cashew Nut Inflorescence Decline in Tripura, a Northeastern State of India PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of an Association of ‘Candidatus Phytoplasma australasia’ with Cashew Nut Inflorescence Decline in Tripura, a Northeastern State of IndiaSurabhi Mitra, Prasenjit Debnath, Amar Bahadur, Suken Chandra Das, Kiran Kirdat, Amit Yadav, and G. P. RaoSurabhi MitraDivision of Plant Pathology, Indian Agricultural Research Institute, New Delhi 110012, IndiaSearch for more papers by this author, Prasenjit DebnathCollege of Agriculture, Tripura, Lembucherra, West Tripura 799210, IndiaSearch for more papers by this author, Amar BahadurCollege of Agriculture, Tripura, Lembucherra, West Tripura 799210, IndiaSearch for more papers by this author, Suken Chandra DasCollege of Agriculture, Tripura, Lembucherra, West Tripura 799210, IndiaSearch for more papers by this author, Kiran KirdatNational Centre for Microbial Resource, National Centre for Cell Science, Sai Trinity Complex, Sus Road, Pashan, Pune 411021, IndiaSearch for more papers by this author, Amit Yadavhttp://orcid.org/0000-0002-4882-9075National Centre for Microbial Resource, National Centre for Cell Science, Sai Trinity Complex, Sus Road, Pashan, Pune 411021, IndiaSearch for more papers by this author, and G. P. Rao†Corresponding author: G. P. Rao; E-mail Address: gprao_gor@rediffmail.comhttp://orcid.org/0000-0003-1057-7826Division of Plant Pathology, Indian Agricultural Research Institute, New Delhi 110012, IndiaSearch for more papers by this author AffiliationsAuthors and Affiliations Surabhi Mitra1 Prasenjit Debnath2 Amar Bahadur2 Suken Chandra Das2 Kiran Kirdat3 Amit Yadav3 G. P. Rao1 † 1Division of Plant Pathology, Indian Agricultural Research Institute, New Delhi 110012, India 2College of Agriculture, Tripura, Lembucherra, West Tripura 799210, India 3National Centre for Microbial Resource, National Centre for Cell Science, Sai Trinity Complex, Sus Road, Pashan, Pune 411021, India Published Online:30 Dec 2019https://doi.org/10.1094/PDIS-08-19-1715-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat 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).The author(s) declare no conflict of interest.