First Report of Bean Common Mosaic Virus Infecting Butterfly pea in Taiwan

Butterfly pea ( Clitoria ternatea ) is a perennial leguminous herb widely used for ornamental purposes, natural blue pigments, and medicinal uses (Hasanah et al. 2023). Bean common mosaic virus (BCMV; Potyvirus phaseovulgaris ), a member of the genus Potyvirus , primarily infects leguminous crops (Tang and Feng 2023). In January 2024, butterfly pea plants showing mosaic symptoms were collected in Wufeng district, Taichung, Taiwan. The presence of a potyvirus was detected by enzyme-linked immunosorbent assay (ELISA) with the monoclonal antibody of potyvirus (Agdia Inc. USA) and reverse transcription polymerase chain reaction (RT-PCR) by the Potyvirus-degenerated primers of HRP-5 (5'-ATGATHGARKCNTGGGG) (Pappu et al. 1998) and Oligo-dT(14). To further confirm the virus species, an approximately 1.2-kb fragment covering the 3′-terminal region of BCMV and containing the complete coat protein (CP) gene was amplified by the primer pair BCMV-u2 (5′-GAGATTGCAGCTAGTGG-3′)/Oligo-d(T)14. Three purified isolates (CT-2, CT-3 and CT-11) were obtained from three successive local-lesion inoculation on Chenopodium quinoa . Sequence analysis revealed these three isolates (CT2/PX648187, CT3/PX648188, CT11/PX648189) sharing more than 95% amino acid identity in the CP region with a BCMV isolate deposited in GenBank (OQ993347) and they are clustered to a group in phylogenetic analysis. Sap from symptomatic butterfly pea tissues was mechanically inoculated onto leaves of C. quinoa and produced systemic local lesions. The virus was retransmitted to butterfly pea, inducing similar symptoms, and also infected mung bean ( Vigna radiata ), causing mosaic symptoms on leaves. A BCMV-specific primer pair BCMV-u4 (5'-GGATGCKGWGAATCTG-3')/BCMV-d (5'-ACTTGCTGCTAACGTTGC-3') amplified the expected 778-bp fragment from infected plant tissues, confirming the presence of BCMV in the tested hosts. In addition, butterfly pea plants showing mosaic symptoms were collected from a field in Kaohsiung (Taiwan, in December 2024), and BCMV was also positively detected by RT-PCR. Amino acid sequence analysis of the CP region showed higher variability in the N-terminal region when compared with BCMV isolates from other leguminous hosts available in GenBank. Viral infections in butterfly pea are mainly characterized by leaf mosaic pattern, which may affect flower color and yield (Jenjai and Samarakoon 2024; Vidana Gamage et al. 2021). Although butterfly pea has previously been listed as a host of BCMV in host records or field surveys, however, experimental confirmation has been lacking. In this study, Koch’s postulates were fulfilled to verify butterfly pea as a natural host of BCMV, and its infection caused uneven flower coloration and reduced ornamental quality. Furthermore, the BCMV isolate from butterfly pea was able to infect mung bean ( V. radiata ), suggesting that BCMV-infected butterfly pea plants might serve as a potential virus source for nearby leguminous crops. To our knowledge, this is the first report of BCMV naturally infecting butterfly pea in Taiwan.