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First Report of Herbacious Hosts for Citrus yellow mosaic badna virus from India

Citrus mosaic disease, a potential threat to citrus production throughout India, is currently an important disease in the southern and northeastern states (2). The reported incidence of the disease ranges from 10 to 77% (K. Gopal, G. S. Aparna, M. Sreenivasuluk, K. V. Subbaiah, and A. R. K. Rao, unpublished data). This yellow mosaic disease of citrus is caused by Citrus yellow mosaic badna virus (CMBV), formerly citrus yellow mosaic disease, (CYMD) (1). Host range studies were done to find herbaceous noncitrus host plant species for virus maintenance. The following are the noncitrus plants tested in this study: Arachis hypogaea, Chenopodium amaranticolor, Chenopodium quinoa, Vigna mungo, Macrotyloma uniflorum, Cicer arietinum, Helianthus annuus, Cajanus cajan, V. sinensis, Cyamopsis tetragonoloba, V. radiata, Pisum sativum, Phaseolus vulgaris, Trichosanthes anguina, Nicotiana tabacum (Harrison special), Dolichos lablab, Petunia × hybrida, Gomphrena globosa, Cucumis melo, Cucumis pepo, Glycine max, Sorghum bicolor, Zea mays, and Canna indica. Young leaves with mosaic symptoms were collected from Citrus sinensis Osbeck, Citrus aurantiifolia Osbeck, and Citrus × limonia Osbeck plants, which are being maintained in an insect-proof glasshouse. The leaves were cut into small pieces, transferred to a chilled mortar, and macerated using 0.01 M phosphate buffer, pH 7.0, containing 0.2% (v/v) of 2-mercapto-ethanol at a tissue/buffer ratio of 1 g/9 ml (wt/vol). The extract was filtered and used for inoculation. The above-mentioned noncitrus plants were uniformly dusted with 600-mesh Carborundum and inoculated with sap extract from the citrus species. The plants were kept in an insect-proof glasshouse and observed for 6 weeks for symptom development. Only three hosts, Canna indica, sorghum, and maize produced visible symptoms. Symptoms were observed 14 days postinoculation on C. indica as chlorotic spots, which later developed into a mosaic pattern. Developing young leaves showed severe mosaic with vein banding symptoms. In sorghum and maize, chlorotic streaks were observed on young leaves after 10 days, which developed into dark green streaks in the leaf lamina. All the inoculated hosts were checked using virus double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) and dot blot ELISA using CMBV polyclonal antiserum (Department of Virology, S.V. University, Tirupati, India). In both tests, only the C. indica, sorghum, and maize samples reacted positively. In dot blot ELISA, as little as 100 ng of virus could be detected in C. indica, sorghum, and maize. Virus from all three citrus sources produced the same symptoms on C. indica, sorghum, and maize. To our knowledge, this is the first report of herbaceous hosts of CMBV, which should prove useful as propagation and index hosts for CMBV.

References: (1) Y. S. Ahlawat et al. Plant Dis. 80:590, 1996. (2) G. S. Reddy et al. Page 130 in: 3rd Int. Symp. Subtrop. Hortic. Bangalore, 1972.