Detection of mixed infection of begomoviruses in cowpea and their molecular characterization based on CP gene sequences

Golden mosaic disease of cowpea in India is known to be caused by Mungbean yellow mosaic India virus (MYMIV). A severe yellow mosaic disease of cowpea in and around Kanpur was prevalent in kharif 2009. Primer pairs designed to get a fragment of DNA containing coat protein gene of four begomoviruses viz., Mungbean yellow mosaic India virus (MYMIV), Mungbean yellow mosaic virus (MYMV), Horsegram yellow mosaic virus (HgYMV), Dolichos yellow mosaic virus (DoYMV) known to infect various leguminous crops in India were used to detect virus(es) associated with golden mosaic disease of cowpea in PCR. All the ten samples assayed gave positive results with MYMIV specific primer pairs and three of them yielded amplicon of expected size with primer pair specific to DoMYV, indicating presence of mixed infection of MYMIV and DoYMV in these cowpea samples. No amplification was obtained with primer pairs specific to MYMV and HgYMV. The sequences of amplified coat protein genes of MYMIV and DoYMV contained a single open reading frame with 774 nucleotides and 257 amino acids and were designated as MYMIV-[CpKn] and DoMYV- [CpKn]. Nucleotide and deduced amino acids sequences of coat protein gene of MYMIV-[CpKn] had respectively, 95–99% and 96–100% similarity with other isolates of MYMIV. Nucleotide and deduced amino acids sequences of coat protein gene of DoYMV-[CpKn] had respectively, 95–96% and 97–98% similarity with other isolates of DoYMV. This appears to be the first report of mixed infection of MYMIV and DoYMV in naturally infected cowpea.