Preliminary analysis of sweet potato feathery mottle virus accumulation in field-collected sweet potato genotypes co-infected with sweet potato chlorotic stunt virus in Costa Rica

Sweet potato (Ipomoea batatas) is a key staple crop in Costa Rica, but its vegetative propagation renders it highly vulnerable to viral infections. Sweet potato virus disease (SPVD), one of the most damaging viral syndromes, arises from co-infection by sweet potato feathery mottle virus (SPFMV; genus Potyvirus) and sweet potato chlorotic stunt virus (SPCSV; genus Crinivirus). This preliminary study investigated SPFMV accumulation in three sweet potato genotypes—Criollo (CRL), Guapileño (GPN) and Beauregard (BRD)—naturally co-infected with SPCSV and examined associated cytopathological alterations. Field samples exhibiting SPVD-like symptoms were confirmed to be co-infected with SPFMV (lineage B) and SPCSV (WA strain) through multiplex reverse transcription PCR and Sanger sequencing. A two-step quantitative reverse transcription PCR (RT-qPCR) targeting the SPFMV coat protein gene was used to quantify viral load. CRL exhibited significantly higher SPFMV titers (5.06 × 10⁶ copies/mg tissue) compared to GPN and BRD. Electron microscopy of CRL leaf tissue revealed typical pinwheel inclusion bodies and chloroplast deformation, consistent with potyvirus-induced cytopathology. These findings reveal differences in SPFMV accumulation among genotypes under field co-infection conditions, which may be influenced by multiple factors including host background and environment.