First Report of Tomato mosaic virus Isolated From Solanum macrocarpon in Nigeria

Abstract

Solanum macrocarpon, also known as African eggplant or gboma, is a plant of the Solanaceae family. It is a tropical perennial plant closely related to eggplant (Oboh et al. 2005). African eggplant originated from West Africa, but is now widely distributed in Central and East Africa and is widely cultivated for food, medicinal purposes, and as an ornamental (Oboh et al. 2005). In April 2016, virus symptoms of mosaic and leaf mottling were observed on African eggplant variety NHS20 in a vegetable farm in Oluseyi-Eleyele, Ibadan Northwest Local Government Area, Nigeria. Routine indexing of symptomatic African eggplant samples using direct antigen coating (DAC)-ELISA with antisera specific for Cowpea mottle virus (CPMoV), Cucumber mosaic virus (CMV), Cowpea mild mottle virus (CPMMV), Cowpea aphid borne mosaic virus (CABMV), Blackeye cowpea mosaic virus (BCMV), Tomato mosaic virus (ToMV), and Tobacco mosaic virus (TMV) was carried out. Detection antibodies were purchased from Agdia (Indiana, U.S.A.). The result showed the presence of ToMV in 19 of 20 samples collected and indexed with optical density (OD) values for ToMV averaging 1.389 while the positive and negative controls had 2.226 and 0.264, respectively. No positive reactions were obtained for CPMoV (avg. OD 0.146, positive control 3.116, negative control 0.149), CMV (avg. OD 0.207, positive control 1.793, negative control 0.119), CPMMV (avg. OD 0.244, positive control 2.632, negative control 0.147), CABMV (avg. OD 0.137, positive control 1.575, negative control 0.196), BCMV (avg. OD 0.167, positive control 1.130, negative control 0.181), and TMV (avg. OD 0.443, positive control 1.372, negative control 0.295). The presence of ToMV was verified with reverse transcription (RT)-PCR using primer sets ToMVFor (5′-CTCCATCGTTCACACTCGTTACT-3′) and ToMVRev (5′-GATCTGTCAAAGTCTGAGAAACTT-3′) (Jacobia et al. 1998). RT-PCR produced a PCR amplicon of expected size (∼500 bp) and the product was purified and sequenced. Nucleotide sequence analysis confirmed the identity of the amplicon to be ToMV. Sequence comparisons showed 100 to 99% identity with known ToMV for coat and movement protein (CP and MP genes) sequences of ToMV isolates in GenBank (LN827938.1 and AAB97422.1). The sequence data were deposited in GenBank (KY751915.1). TMoV was confirmed in African eggplants in two other locations visited. The virus was readily transmitted by mechanical inoculation to 10 stands each of pepper, tomato, and African eggplants (S. macrocarpon) obtained from the National Horticultural Research Institute (NIHORT). All plants inoculated tested positive for ToMV in ELISA and RT-PCR, although there were no visible symptoms on the pepper (NH1V) plants. The inoculated tomato (Ibadan local) and African eggplants (NHS20) showed mosaic, mottle, and yellowing of leaves similar to symptoms observed on field-infected African eggplant. ToMV has also been found to infect many solanaceous plants but occurrence from this particular species has not been documented, although a number of viruses infecting the commonly distributed eggplant, S. melongena L., have been reported from many parts of the world (Chen et al. 2001). However, Eggplant mottle crinkle virus and TMV have been reported to cause severe mosaic disease in African eggplant in Cameroon (Chen et al. 2001). ToMV has not been previously reported to infect S. macrocarpon. To our knowledge, this is the first report of ToMV on African eggplant in Nigeria. Additional work is needed to investigate the spread of ToMV and its interaction with other Solanaceous plants in Nigeria and the need for research to develop more effective management options.