Prevalence of Apple stem grooving virus: biological, serological and molecular studies-An Indian perspective

Surveys conducted during 2009 in 20 apple orchards of Shimla district of Himachal Pradesh situated in north western Himalayan region of India revealed viral disease incidence ranging from 5 to 95 per cent. Curling and puckering coupled with necrotic lesions on apple leaves were the predominant symptoms. An orchard having 95 per cent incidence of viral diseases was selected for conducting biological and serological detection of Apple stem grooving virus (ASGV). Serological detection through enzyme-linked immunosorbent assay (ELISA) resulted in the confirmation of ASGV infection in all the samples of 10 cultivars randomly marked for assays. Biological detection of one of the ASGV isolates on herbaceous hosts resulted in the production of symptoms on Chenopodium quinoa, Phaseolus vulgaris, Nicotiana glutinosa and few other hosts. Detection on Virginia crab woody indicator under field conditions through double grafting of inoculator and indicator budwood produced no viral symptoms on leaves whereas brown line necrosis was produced at the graft union. Leaf samples drawn during April to August months were found suitable for the detection of ASGV in ELISA beside petals being the best source. Association of ASGV with viral symptoms in apple was further confirmed by reverse transcriptase polymerase chain reaction (RT-PCR) with an amplified PCR product of Coat Protein gene of 755 bp, which was cloned and sequenced. Sequence analysis of CP gene in BLASTN showed 99% homology with JX080201 sequence from Germany and phylogenetic analysis revealed that ASGV isolate reported in this study showed common ancestry with Brazilian isolate (AF438409).