Citrus mosaic disease in India is associated with a badnavirus
Studies on citrus mosaic disease (EU Annex II/A1) have been carried out in India, in collaboration with USA. This disease is widely distributed in India, especially on sweet orange (Citrus sinensis) and pummelo (Citrus grandis). Symptoms in the field are characterized by a bright yellow mottling of the leaves and yellow flecking along the veins. Citrus mosaic disease seems to be of great economic importance to the Indian citrus industry. For example, the incidence of the disease ranges from 10 to 70 % in Satgudi sweet orange orchards in Andhra Pradesh. Losses were apparent on Satgudi sweet orange in Andhra Pradesh and Karnataka, as several orchards with trees of 4 to 10 years old were abandoned since they were no longer productive. Reduction of fruit yield could reach 77 % in trees of 10 years old, and fruit from affected trees could present a 10 % reduction in juice and ascorbic acid. Citrus mosaic disease has been recorded in up to 46 % of trees in some commercial nurseries at Kodur (Andhra Pradesh). Its occurrence in nurseries suggested that transmission could occur through budwood.
The authors have shown that a previously unreported badnavirus was associated with this disease. The virus had 30 x 150 nm non-enveloped bacilliform particles typical of badnaviruses. ISEM studies revealed that the virus is serologically related to sugarcane bacilliform badnavirus and to 8 other badnaviruses. PCR using oligonucleotide primers specific to badnaviruses gave a product similar in size to that obtained with other badnaviruses which have been shown to contain dsDNA genomes. The name citrus mosaic badnavirus was proposed, and it is noted that this is the first report of a badnavirus in citrus. The authors have also found that the virus could be transmitted by grafting and dodder to 13 of 14 citrus species and cultivars commonly used, but not by the aphids (Myzus persicae, Aphis gossypii) and mealy bugs (Planococcus citri) tested. It was also transmitted by mechanical inoculation from symptomatic citrus to healthy Citrus decumana, a native citrus species in India.
It can be recalled that mosaic diseases of citrus have so far been only reported from India and Japan. The authors have observed in previous studies (unpublished) that citrus mosaic badnavirus was not serologically related to the Japanese citrus mosaic. In addition, the Japanese mosaic disease is associated with isometric particles, and is thought to be a strain of satsuma dwarf 'nepovirus' (EPPO A2 quarantine pest).
Sources
Ahlawat, Y.S.; Pant, R.P.; Lockhart, B.E.L.; Srivastava, M.; Chakraborty, N.K.; Varma, A. (1996) Association of a badnavirus with citrus mosaic disease in India.
Plant Disease, 80(5), 590-592.