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Specific Detection of Potato Virus A in Dormant Tubers by Reverse-Transcription Polymerase Chain Reaction

A reverse-transcription polymerase chain reaction (RT-PCR) protocol was developed for the detection of potato virus A (PVA) in dormant tubers. A 255-bp amplified product was produced using a primer pair from the P1 gene of the PVA genome. The 255-bp product was detected in nucleic acids from leaves, tubers, and purified virions and was specific to PVA as determined by Southern blot tests and detection by a PVA-specific probe. When presented with seven potato virus/strain nucleic acids and a viroid, singly and in mixed infections, the primer pair did not amplify any products. Its specificity to PVA was further demonstrated by RT-PCR detection of PVA from the known mixtures of PVA and potato virus Y samples. PVA was detected in foliage nucleic acids at a dilution of 1:1024--1:4096 and tuber nucleic acids at 1:256--1:1024. It was uniformly present in various parts of the potato tuber. PVA was detected in composite tuber samples containing a ratio of infected to healthy sap of 1:29 and was readily detected in tubers of several cultivars or breeding lines, in dormant as well as in sprouting tubers stored at 20--25°C for 4 months.