Neth. J. P1. Path. 94 (1988) 149-160 Detection of tobacco rattle virus in different parts of tulip by ELISA and cDNA hybridisation assays C.I.M. VAN DER VLUGT1, 3, H.J.M. LINTHORST2, C.J. ASJES3, A.R. VAN SCHADEWIJK1 and J.E BOL2 1 Bulb Inspection Service, Postbus 300, 2161 AH Lisse, the Netherlands 2 Department of Biochemistry, State University Leiden, Wassenaarseweg 64, 2333 AL Leiden, the Netherlands 3 Bulb Research Centre, Postbus 85, 2160 AB Lisse, the Netherlands Accepted 23 December 1987 Abstract Different parts of tulips cv. Apeldoorn were assayed for the presence of tobacco rattle virus (TRV) by means of ELISA, cDNA hybridisation and immuno-electron microscopy. Assays were periodically performed during the growing season and upon storage of the bulbs. During the growing season in the field the relative TRV concentrations detected by ELISA and cDNA were highest mainly in the basal stem-parts and basal leaf-parts, respectively. When, during storage, infected bulbs were divided into a number of sections, TRV could be detected only in some of the sections, irrespective of the test used. However, nearly all sprouts of infected bulbs, stored at 5 ~ for 7 months, appeared to contain detectable amounts of TRV upon testing with ELISA and cDNA. Thus, testing of sprouts may offer a possibility to develop a routine test for TRV in tulip bulbs in due course. Additional keyword." localisation. Introduction Covering a total land area of about 70 km 2, tulips are one of the most important com- mercially grown bulbous crops in the Netherlands. Of the viruses found in tulip, tulip breaking virus (TBV) and tobacco rattle virus (TRV) occur most frequently (Asjes and Elbertsen, 1982). Both viruses in tulips can be detected in the field by visual inspection as the viruses produce characteristic symptoms (Asjes en Elbertsen, 1982; Van Slogteren, 1958). Screening, however, should be done preferentially with the bulbsto fit into a sample inspection as part of a general quality inspection. TBV is detected reliably by ELISA (Van Schadewijk and Eggink, 1984) in homogenates of tulip and lily bulbs; over 700 000 ELISA assays are carried out each year by the Bulb Inspection Service in the Netherlands to prevent the use of infected propagation material. In con- trast, preliminary experiments on the detection of TRV in bulb homogenates yielded unsatisfactory results with ELISA (unpublished results). This may be partly due to technical problems such as a low concentration of the virus or the presence of inhibitory substances in the homogenates. In addition, the rather antigenic variability among tobraviruses (Harrison and Robinson, 1986) may cause a fundamental problem in that probably many antisera are required to detect all possible serotypes. 149