Detection of Potato Spindle Tuber Viroid in Field-Grown Potatoes by an Improved Electrophoretic Assay

Abstract

An improved polyacrylamide gel electrophoresis (PAGE) procedure was developed for more efficient detection of potato spindle tuber viroid (PSTV). Modification in sample preparation permitted sample processing in 3 h and completion of PSTV detection in 1 day. Inclusion of xylene cyanole, which comigrates with PSTV in gels, eliminated confusion due to the occasional appearance of extraneous RNA bands or uneven migration in individual gels. Photography of gels stained with ethidium bromide and illuminated with UV light enhanced PSTV detection. Reliability of the procedure was investigated by assaying 14 cultivars of field-grown potatoes (Solanum tuberosum) at monthly intervals. When potatoes were grown from infected tubers, PSTV was detected in all assays. Detection of current-season infections increased 20% at 1 mo. to 70% at 2 mo. postinoculation. In current-season infections, PSTV detection was not affected by different PSTV strains (mild or severe). The concentration of PSTV in stem apices of the 14 cultivars varied 0.64 to 2.20 .mu.g/g of tissue and was not correlated with symptom severity.