First report and molecular identification of two new begomovirus strains linked to okra enation leaf curl disease in northern and southern India

Okra (Abelmoschus esculentus) is an important vegetable crop of the Malvaceae, extensively grown in the Indian subcontinent. Okra enation leaf curl virus (OELCuV) has emerged as a significant threat to okra cultivation in India and is responsible for okra enation leaf curl disease (OELCuD) in India. This study aimed to investigate the cause and distribution of OELCuD in northern and southern India, focusing on Uttar Pradesh and Tamil Nadu. A survey conducted from 2020 to 2022 recorded OELCuD incidence of 17.37% in Meerut (Uttar Pradesh) and 63.3% in Viluppuram (Tamil Nadu). While this marks the first report of OELCuD in Meerut, its presence in Viluppuram indicates its continued spread. Symptomatic okra leaf samples were collected from both regions for molecular characterization to assess the disease's impact on okra production. The association of begomovirus with infected samples was confirmed through PCR with OELCuV coat protein gene- specific primers, which resulted in the expected amplicon (c. 770 bp).The full genome (DNA-A) was amplified by genome rolling circle amplification (RCA). The amplified RCA product was cloned, sequenced, and analyzed. The pairwise alignment and phylogenetic analysis revealed that the isolate from Viluppuram showed a maximum identity of 85.50% with GU112010 and 92.90% with MK084766 OELCuV isolates, while the Meerut isolate showed 92.60% identity with GU111996 and MK084765 isolates of OELCuV. Based on species demarcation criteria for begomoviruses, both the isolates are identified as new strain of Okra enation leaf curl virus and proposed the name Okra enation leaf curl virus [India: Meerut: Uttar Pradesh: 2023] and Okra enation leaf curl virus [India: Viluppuram: Tamil Nadu: 2023]. Further, recombination analysis revealed a single intra-specific recombination event in the genomic region in both the isolates understudy. This discovery is significant for understanding the spread of the OELCuD and provides valuable insights into the genetic diversity and recombination of the causal virus, particularly in regions where the OELCuV had not been previously reported.