Cajanus scarabaeoides yellow mosaic virus, a new bipartite begomovirus causing yellow mosaic disease in Cajanus scarabaeoides (L.) Thouars in India.

Abstract

Yellow mosaic disease of Cajanus scarabaeoides (L.) Thouars (CsYMD) was observed in up to 46% of C. scarabaeoides plants in the mungbean, urdbean and pigeon pea fields from 22 districts of Chhattisgarh State, India, during 2017-2019. The symptoms were characterized by yellow mosaic on green leaves and yellow discoloration of leaves in advanced stages of the disease. Severely infected plants showed shortened internodal length and reduced leaf size. CsYMD was transmissible to healthy C. scarabaeoides and Cajanus cajan by whitefly (Bemisia tabaci). The plants thus infected developed typical yellow mosaic symptoms on their leaves within 16 and 22 days of inoculation, respectively, suggesting a begomovirus etiology. Molecular analysis revealed that this begomovirus has a bipartite genome composed of DNA-A (2729 nucleotides) and DNA-B (2630 nucleotides). Sequence and phylogenetic analyses revealed that the nucleotide sequence of the DNA-A component had the highest identity of 81.1% with DNA-A of Rhynchosia yellow mosaic virus (RhYMV) (NC_038885) followed by mungbean yellow mosaic virus (MN602427) (75.3%). DNA-B had the highest identity of 74.0% with DNA-B of RhYMV (NC_038886). As per ICTV guidelines, this isolate had <91% nucleotide identity with DNA-A of any of the begomoviruses reported, hence, it is proposed as a new begomovirus species, tentatively named Cajanus scarabaeoides yellow mosaic virus (CsYMV). After agroinoculation with DNA-A and DNA-B clones of CsYMV, all Nicotiana benthamiana plants developed leaf curl symptoms along with light yellowing symptoms 8-10 days after inoculation (DAI), while ~60% of the C. scarabaeoides plants developed yellow mosaic symptoms similar to those observed in the field 18 DAI, thus fulfilling the Koch's postulates. From these agro-infected C. scarabaeoides plants, CsYMV was transmissible to healthy C. scarabaeoides plants by B. tabaci. Apart from these hosts, CsYMV also infected and caused symptoms in mungbean and pigeon pea.