DIAGNOSIS OF POTATO LEAFROLL VIRUS (PLRV) IN PROGENY OF PRIMARILY INFECTED POTATO PLANTS

Effects of the term of the ELISA diagnosis (in the autumn and in the s pring) and its technological procedures (diagnosis of greenhouse plant s of potatoes after breaking of tuber dormancy by gibberellic acid and diagnosis on tuber sprouts after rindite treatment) on the reliabilit y of the PLRV detection in the progeny of primarily infected plants fr om field provocative conditions were evaluated. Six potato cultivars w ith different maturity and resistance to PLRV were evaluated in four y ears with different level of infection pressure. After natural termina tion of vegetation period, two to three tubers from each plant were ta ken Both the diagnoses were performed on identical tubers in each term . ELISA was conducted as described by Clark, Adams (1977) with minor m odifications (Dedic, 1985). Diagnostic kit purchased from Bioreba (Swi tzerland) was used throughout the experiments. Absorbance (A(405)) val ues were determined by a Dynatech spectrofotometer (MR 700) and reacti ons were rated as positive if they exceeded a threshold value equal to the mean absorbance of the healthy control plus three times its stand ard deviation, and were higher than 0.1 optical unit. In the years wit h low infection pressure (1986, 1987) very good agreement of results o f diagnosis were documented both in the assortment of all cultivars te sted (97 to 100 %) and also in the evaluation of parallel samples (88 to 100 %). In the years with severe infection pressure (1988, 1989), t he two diagnostic procedures were compared also in spring months. The results are presented in Tabs I and II. In autumn period the overall a ccord attained 98 % in both years, considering individual cultivars it was 92 to 100 %. In spring period the overall agreement was ranging f rom 93 to 99 %, and the individual cultivars reached 87 to 100 %. By m eans of diagnosis utilizing potato sprouts, less infected tubers were detected than with those leaves, especially in the spring evaluation o f some cultivars. Uneven translocation of PLRV into particular tubers of potato plant after natural infection in field conditions was noted both in cultivars with higher resistance rating and in more susceptibl e ones. In average of all the cultivar tested, the overall accord of d iagnosis in parallel (sister) tubers attained 86 to 89 % and was in th e range of 75 to 98 % depending on the cultivars (Tab. III). The resul ts are discussed with the recent data dealing with investigated proble ms. From these results can be concluded that the contemporary modifica tion of DAS-ELISA utilizing potato sprouts is not recommended unambigu ously for the large-scale and reliable diagnosis of PLRV.