Identification and distribution of viruses infecting sweet potato (Ipomoea batatas L.) in KwaZulu-Natal province, South Africa

Abstract

A survey to determine occurrence and distribution of viruses infecting sweet potato (Ipomoea batatas (L.) Lam.) was conducted in major sweet potato growing areas in KwaZulu-Natal (KZN), South Africa. Eighty-four symptomatic vine samples were collected and graft-inoculated onto universal indicator plants, Ipomoea setosa Ker. Gawl. and Ipomoea nil (L.) Roth. Six weeks post-inoculation, typical sweet potato virus-like symptoms of chlorotic flecking, leaf deformation, stunting, chlorotic mosaic, and distinct interveinal chlorotic patterns were observed on indicator plants. Under a transmission electron microscope, negatively stained preparations of crude leaf sap and ultra-thin sections from symptomatic grafted I. setosa plants revealed the presence of elongated flexuous particles and pinwheel-type inclusion bodies that are characteristic to the cytopathology of potyviruses. A majority of leaf samples (52%) from graft-inoculated indicator plants tested positive for virus and showed occurrence of Sweet potato feathery mottle virus (SPFMV), Sweet potato mild mottle virus (SPMMV), Sweet potato chlorotic stunt virus (SPCSV), Sweet potato chlorotic fleck virus (SPCFV), Sweet potato virus G (SPVG), Sweet potato mild speckling virus (SPMSV) and Sweet potato caulimo-like virus (SPCaLV) using nitrocellulose membrane enzymelinked immunosorbent assays. The most frequently detected viruses were SPFMV (39%), SPVG (30%), followed by SPCSV (13%) and SPMMV (12%). SPCaLV and SPCFV at 10% and SPMSV at 7% were found exclusively in samples collected from one area. Reverse-transcription polymerase chain reaction of total plant RNA isolations confirmed the presence of SPFMV, SPVG, SPCSV and SPMMV as the most prevalent viruses infecting sweet potato in KZN.