First record of a Hop stunt viroid variant on Nagpur mandarin and Mosambi sweet orange trees on rough lemon and Rangpur lime rootstocks

P. Ramachandran¹*, J. Agarwal¹, A. Roy², D. K. Ghosh³, D. R. Das¹ and Y.S. Ahlawat¹

1 Plant Virology Unit, Division of Plant Pathology, Indian Agricultural Research Institute, New Delhi – 110012, India
2 Plant virus Lab., Division of Crop Protection, Central Research Institute for Jute and Allied Fibres, Barrackpore, Kolkata – 700 120, India
3 NRC for Citrus, Nagpur, India

*viroidram@yahoo.co.in

Accepted for publication 22/12/04

Citrus rootstocks 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) (7 plants) and mosambi (C. sinensis) (10 plants) grafted on rough lemon and Rangpur lime rootstocks (Fig. 1). Following grafting of scions from all these plants onto Etrog Citron (C. medica), an indicator host for Citrus exocortis viroid (CEVd), an unusual symptom of reduced size and yellowing of newly emerging leaves developed. This prompted further investigation.

Figure 1: Symptoms of bark scaling and bark splitting on on rough lemon (left) and Rangpur lime (right) rootstocks

Electrophoresis under denaturing conditions of total nucleic acid extracted from the grafted Etrog citron plants with symptoms, indicated the presence of viroid-like low molecular weight (LMW) RNA in all the samples. These LMW-RNAs were used in RT-PCR using a set of citrus viroid specific primers (Ramachandran et al., 2003). Amplicons of ~300 bp were obtained in all the samples with primers specific to Hop stunt viroid (HSVd), while no amplification was observed with CEVd specific primers. Cloning and sequencing of these amplicons identified a viroid RNA (Acc. No. AY237168) with 100% sequence similarity to HSVd-Ca905 (Acc. No. AF131250; Reanwarakorn & Semancik, 1999) and HSVd-ycv (Acc. No. AJ490824; Roy & Ramachandran, 2003). This constitutes the first isolation of a HSVd isolate (HSVd-RL) from citrus rootstocks showing bark scaling and splitting symptoms in Central India. This result suggests that HSVd is also a component in producing bark-scaling symptoms in rootstocks, which were previously considered to be due to CEVd-infection alone. This report indicates the need for the testing of citrus plants for HSVd in budwood certification and germplasm evaluation.

References

Ahlawat YS, 1997. Viruses, greening bacterium and viroids associated with citrus (Citrus spp.). Indian Journal of Agricultural Science 67, 51-57.

Roy A, Ramachandran P, 2003. Occurrence of a Hop stunt viroid (HSVd) variant in yellow corky vein disease of citrus in India. Current Science 85, 1608-1612.

Ramachandran P, Roy A, Mathur S, Agarwal J, Ahlawat Y S, 2003. Diagnostic for Citrus exocortis and Hop stunt viroids associated with yellow corky vein disease in citrus. Indian Phytopathology 56(4), 428-433.

Reanwarakorn K, Semancik JS, 1999. Correlation of hop stunt viroid variants to cachexia and xyloporosis diseases of citrus. Phytopathology 89, 568-574.

The British Society for Plant Pathology