Avocado sunblotch viroid (ASBVd) is a circular and single-stranded RNA viroid (genus Avsunviroid) with a genome of about 250 nucleotides in length (Roberts et al., 2023). It causes sunblotch disease in infected avocado. The viroid is transmitted through infected propagation material, pollen and seed. ASBVd has been reported in most avocado-producing areas and causes significant reductions in yield and fruit quality (Carabez et al., 2019).

  In December 2022, plants of avocado (Persea americana) cv Hass exhibiting cracked bark, multiple sunken yellowish crevices on the fruits and leaves with variegated areas were observed in an orchard in Murang'a County, Kenya. The disease incidence was about 5% in the 3.1 hectare field. Ten diseased fruits were sampled to be tested for ASBVd. Four fruits from asymptomatic trees were also sampled.

  Total RNA was extracted from both diseased and asymptomatic samples using CTAB. A two-step RT-PCR assay was done using the extracted RNA and ASBVd-specific primers which amplify 88 to 104 nucleotides (Schnell et al., 1997). The amplified products were visualised using gel electrophoresis and amplicons of the expected size were obtained from all diseased fruits. No amplification was obtained from the asymptomatic fruits. The amplicons from three samples were Sanger sequenced bidirectionally and found to be identical (GenBank Accession No. OQ871564). A BLASTn search of the sequence revealed that it shared 99.37% identity with an isolate. from Uruapan, Mexico (KF562705). A phylogenetic tree was constructed using the Maximum Likelihood method (MEGA X program) with ASBVd sequences from different geographical locations.

 Source of information:https://bsppjournals.onlinelibrary.wiley.com/doi/full/10.1002/ndr2.12212