Distribution and host range of viruses associated with the citrus leprosis disease complex in Mexico

Citrus leprosis virus C (CiLV-C) (Cilevirus) and orchid fleck virus citrus strain (OFV-Cit) (Dichorhavirus) are viruses associated with citrus leprosis disease. Although symptoms associated with CiLV-C were observed in orange in 2005 in Mexico, and confirmed using molecular techniques in 2011, no studies have been made on the distribution of either CiLV-C or OFV-Cit viruses. During 2017, we studied the geographical distribution and host range of these two viruses infecting citrus orchards in Mexico, specifically orange, lime, mandarin and grapefruit orchards in 15 Mexican states. Furthermore, in 2019 we sampled lime orchards in three Mexican states. Presence of CiLV-C and OFV-Cit was determined using reverse transcription polymerase chain reaction (RT-PCR) assays. During 2017 the proportion of leaves infected by either CiLV-C or OFV-Cit was significantly affected by geographical origin. However, only a few samples were obtained from mandarin and grapefruit so these data were excluded from statistical analysis; orange had significantly higher rates of infection with CiLV-C than lime and the opposite was observed for OFV-Cit. Using RT-PCR, some asymptomatic leaves from 2017 samples were positive for the viruses of interest. In 2019 no symptoms associated with leprosis were observed in any of the leaves sampled from lime orchards. However, low infection rates were detected, with 6% of samples testing positive for CiLV-C and 3% for OFV-Cit. To confirm the identity of the CiLV-C isolate found in lime leaves collected in 2019, we sequenced nearly the complete RNA2 genomic region of the virus. Basic Local Alignment Search Tool (BLAST) search revealed 98.99% similarity with previously reported CiLV-C sequences from other citrus species. The implications of our results for field monitoring and disease detection are discussed.