Characterization of novel strain of Candidatus Phytoplasma aurantifolia infecting cowpea (Vigna unguiculata L.)

An attempt was made to characterize the Phytoplasma in suspected cowpea (Vigna unguiculata L.) samples showing symptoms consisting of bud proliferation and stunting at Experimental Farm, ICAR-NBPGR, New Delhi during Kharif 2020. Associated phytoplasma was characterized based on sequence analysis of target 16S rDNA fragments of 1247 bp amplified from symptomatic samples of cowpea by nested-polymerase chain reaction assay using universal phytoplasma specific primers pairs (P1/P7 and R16F2n/ R16R2). The 16S rDNA sequences understudy shared 98.6% similarity with that of the Candidatus Phytoplasma aurantifolia (GenBank accession: U15442). In phylogenetic analysis, the target 16S rDNA fragment from two samples (Cow-1 and Cow-2) clustered with strains of the 16SrII group of Ca. Phytoplasma aurantifolia. The virtual RFLP pattern showed the highest similarity with the reference pattern of the 16SrII-D subgroup (GenBank accession: Y10097) with a coefficient of 0.97. Since obtained coefficient value is equal to the threshold (0.97) for designating a different strain. Therefore, this phytoplasma infecting cowpea is proposed to be a new strain of Ca. P. aurantifolia as 16SrII-Y subgroup.