DIFFERENTIATION AMONG POTYVIRUSES INFECTING SWEET-POTATO BASED ON GENUS-SPECIFIC AND VIRUS-SPECIFIC REVERSE TRANSCRIPTION-POLYMERASE CHAIN-REACTION

Knowledge of virus diseases affecting sweet potato has been complicate d due to the frequent occurrence of mixed infections and difficulties in isolating and purifying sweet potato viruses. A combined assay of r everse transcription and polymerase chain reaction (PCR) utilizing deg enerate genus-specific primers POT1 and POT2 was applied to 18 sweet p otato clones from China. The primers were designed to amplify the vari able 5' terminal region of the potyvirus coat protein gene. Molecular analysis of the amplified fragments identified the Chinese strains of sweet potato feathery mottle virus (SPFMV-CH), sweet potato latent vir us (SPLV-CH), and sweet potato virus G (SPVG-CH). Among the detected p otyviruses, a distantly related strain of SPFMV-CH, tentatively named SPFMV-CH2, was identified in sweet potatoes from China. On the basis o f sequence identity, SPFMV-CH2 was closely related to the common (-C) strain of that virus. Identification of a closely related strain of SP VG-CH in one sweet potato clone from China further illustrated the use fulness of broad-spectrum PCR for detecting uncharacterized viruses. T he acquisition of sequence information permitted the design of virus-s pecific primers for detecting and differentiating SPFMV, SPLV, and SPV G.