P.32. First record of bark splitting and scaling in citrus root-stocks, rough lemon (Citrus jambhiri) and Rangpur line (C. limonia) in central India - associated with a Hop stunt viroid variant

Rootstocks in citrus play a very significant role in tree health and productivity. The sub-viral pathogens, viroids pose a major threat to trees and susceptible rootstocks as they bring about slow decline (Ahlawat, 1997). In a survey of citrus orchards in certain parts of Central India, symptoms of bark scaling, bark splitting and leaf yellowing were observed on Nagpur mandarin (C. reticulata) and mosambi (C. sinensis) grafted on rough lemon and Rangpur lime rootstocks. Grafting on Etrog Citron (C. medica), an indicator host for Citrus exocortis viroid (CEVd), developed unusual symptom of smalling and yellowing of newly emerging leaves. This prompted us for further investigation. Electrophoresis of total nucleic acid extract under denaturing conditions indicated the presence of viroid-like low molecular weight RNA, which was used for RT-PCR using a set of citrus viroid specific primers (Ramachandran et al., 2003). Amplicons of ∼ 300 bp was obtained with primers specific to HSVd while no amplification was observed with CEVd specific primers. Cloning and sequencing of the amplicon showed that it is a viroid RNA (Acc. No. AY237168) with 100% sequence similarity to HSVd-Ca905 (Acc. No. AF131250, Reanwarakorn and Semancik, 1999) and HSVd-ycv (Acc. No. AJ490824, Roy and Ramachandran, 2003). This constitutes the first report of isolation of HSVd variant from citrus rootstocks showing bark scaling and splitting symptoms in Central India. The result suggested that HSVd is also a component in producing bark-scaling symptoms in rootstocks, which were so far considered due to CEVd infection alone. The report thus necessitates testing of citrus germplasm for freedom not only from CEVd but also from HSVd.