Factors affecting the detection of potato leafroll virus in potato foliage by enzyme-linked immunosorbent assay

Using antiserum globulins that reacted only weakly with plant materials, potato leafroll virus (PLRV) at 10 ng/ml was detected consistently by enzyme-linked immunosorbent assay (ELISA). The reaction with PLRV particles was slightly impaired in potato leaf extracts that were diluted less than 10^-1 but not at greater dilutions. Antiserum globulins that reacted more strongly with plant materials could be used satisfactorily for coating microtitre plates but were unsuitable for conjugating with enzyme. The detection end-point of PLRV, in leaf sap of potato cv. Cara plants grown from infected tubers in the glasshouse, was about 10^-2 and the virus was reliably detected in extracts of composite samples of one infected and 15 virus-free leaves. PLRV concentration was much less in extracts of roots or stolons than in leaf extracts. The virus was detected in infected leaves of all 27 cultivars tested. PLRV was readily detectable 2 wk before symptoms of secondary infection developed in field-grown plants of cv. Cara and Maris Piper and remained so for at least 5 wk. Its concentration was slightly greater in old than in young leaves and was similar to that in glasshouse-grown plants. In field-grown plants of cv. Maris Piper with primary infection, PLRV was detected in tip leaves 21–42 days after lower leaves were inoculated by aphids; in some shoots it later reached a concentration, in tip leaves, similar to that in leaves with secondary infection. Symptoms of primary infection developed in the young leaves of some infected shoots but were inconspicuous and were not observed until at least a week after PLRV was detected by ELISA.