Genome reconstitution and nucleic acid hybridization as methods of identifying particle-deficient isolates of tobacco rattle virus in potato plants with stem-mottle disease

NM isolates of tobacco rattle virus (TRV) are perpetuated by the larger genome nucleic acid (RNA-1) but do not produce nucleoprotein particles; their identification therefore presents special problems. Assays of the infectivity of nucleic acid extracts, and of previously frozen sap, suggested that such isolates occur in potato plants with stem-mottle disease. These isolates were identified by two tests. In the first, TRV nucleoprotein particles were produced in plants inoculated with a mixture of nucleic acid from diseased potato leaves and non-infective RNA-2 of an authentic culture of TRV, showing that the TRV genome had been reconstituted. In the second test, TRV RNA was identified in nucleic acid from diseased potato leaves by hybridization to 3H-labelled DNA complementary in nucleotide sequence to RNA-1 of the PRN strain of TRV. This cDNA test consistently identified TRV in stem-mottle affected potato plants grown in the glasshouse or in field crops. Although particle-producing isolates of TRV have been reported in potato, stem-mottle disease is apparently usually caused by infection with NM isolates.