First report of Citrus tristeza virus associated with stem-pitting of Citrus decumana in India.

Abstract

Citrus changshanensis cv. Huyou is one of the major citrus cultivars in eastern China. More than 90% of Huyou trees are grown on trifoliate orange (Poncirus trif oliata), a rootstock with high degree of resistance to Citrus tristeza virus (CTV) (Garnsey et al ., 1987). A new disease characterized leaf yellowing and decrease of marketable fruit production has emerged in many cv. Huyou orchards of Zhejiang province. Twenty-five symptomatic and 11 symptomless leaf samples were collected in April 2010 and February 2011 from seven different cv. Huyou orchards. Samples were tested by TAS-ELISA using CTV-specific commercial kits (Agdia, USA). Twenty-one of the 25 symptomatic samples reacted positively whereas no reaction was obtained from symptomless leaves. Total RNA was extracted from the leaves of a citrus accession denoted CS-7, reverse transcribed using primer CP3, then PCR-amplified with the degenerate primer pairs CP1 and CP3 (Giflings et al ., 1993), and primers CTCpol and CTCpo2 (Kim et al ., 2000) specific for CTV major and minor coat proteins, respectively. Two PCR fragments of 670 and 750 bp were obtained for the major and minor protein, respectively. Three independent clones were sequenced for each fragment, and representative sequences were deposited in GenBank under accession Nos HQ634290 and HQ634291. BLASTn search and phylogenetic analysis indicated that CTV isolate CS-7 is closely related to several CTV isolates from New Zealand that overcome trifoliate orange resistance (Harper et al ., 2010). The emergence of a trifoliate orange resistance-breaking CTV isolate in this region may cause serious damage to cv. Huyou. To our knowledge this is the first report of CTV in cv. Huyou in Zhejiang.