Current status of Citrus tristeza virus incidence and its spatial distribution in citrus growing geographical zones of India

Abstract

Citrus tristeza virus (CTV), a member of genus Closterovirus, is an important pathogen which has destroyed more than one million citrus trees in India till date. Survey was conducted in commercial Citrus sp. covering all the citrus growing geographical zones of India. For detection of CTV and estimation of disease incidence, direct antigen coated- enzyme linked immuno-sorbent assay (DAC-ELISA), reverse transcription- polymerase chain reaction and nucleotide sequence analyses were employed. The overall CTV incidence of 26.3% in Vidarbha region, 47.1-56.0% in Northeast (Asom, Meghalaya, Sikkim and the Darjeeling hills), 36-50% in South (Andhra Pradesh and Karnataka) and 16-60% in North-Northwest (Uttarakhand, Delhi and Punjab) were reported. CTV titre in infected tree samples of different locations was measured by ELISA . The high titre was observed in Kagzilime (C. aurantifolia) and sweet orange (C. sinensis) but low in mandarin (C. reticulata). Nucleotide sequence of 5’ORF1a fragment of CTV genome of nine representative CTV isolates, Kat-8, RA-3, B-6, Dh-1, An-9, TP-4, Pant-3, MU-2 and As-2 from all the citrus growing regions surveyed were analysed. The present Indian isolates showed 78-98% identities among them, and placed in different clusters in phylogenetic analysis. This is for the first time an overall incidence of CTV and its spatial distribution in citrus growing geographical zones of India were reported. Findings presented in this study will help in understanding epidemiology and formulating molecular based management strategy.