Cydonia oblonga as reservoir of Apple Chlorotic Leaf Spot Virus in India

Cydonia oblonga known as “Quince” belongs to Rosaceae family. It has traditionally been used as medicine and flavouring agent (Kartikar et al., 1981). Moreover, it is a valued dwarfing rootstock for pear which produces more fruit-bearing branches and has accelerated fruit maturity when used in this way. Quince is a natural host to several virus and virus-like diseases infecting apple and other rosaceous species, though it has not been described as primary host for any virus (Sutic et al., 1999). Apple chlorotic leaf spot virus (ACLSV), type species of the genus Trichovirus (Martelli et al., 1994), induces severe graft incompatibilities in some Prunus combinations, causing major problems in nurseries.

In surveys conducted in Salooni valley (Himachal Pradesh, India), leaves showing distortion and yellow spots were collected from quince grown between the apple orchards. Preliminary testing was done using ELISA for apple mosaic virus, ACLSV (Agdia,USA) and apple stem grooving virus (Loewe, Germany) as per the manufacturers' instruction. Only ACLSV antibodies reacted positively. To rule out possibility of other viruses, host range studies were carried out. Chenopodium amaranticolor showed small chlorotic spots in inoculated leaves. A single lesion was inoculated onto Chenopodium quinoa which gave chlorotic and necrotic spots on inoculated leaves, followed by chlorotic spots in upper leaves.

For further confirmation degenerate primers for amplification of complete coat protein and part of 3'UTR region of ACLSV were designed (Accession Nos. AM490253 and AM490254). RT-PCR using these primers gave an amplicon of approximately 800 bp which was cloned and sequenced (Acc. No. AM498049). The nucleotide sequence was analysed and compared with the partial coat protein of ACLSV reported in quince from Greece (Acc. No. AM292923). Pairwise comparison was performed using B12seq program. The sequence exhibited nucleotide and amino acid similarity levels of 84% and 87% respectively which is in accordance to the accepted range of variability within species (Adams et al., 2004). This is the first report confirming the presence of ACLSV in quince from India and first complete coat protein of ACLSV from quince.