IMMUNOENZYMATIC DIAGNOSIS OF POTATO-VIRUS -Y (PVY) IN PROGENY OF PRIMARILY INFECTED POTATO PLANTS

The effects of the date of the ELISA diagnosis (in autumn and in sprin g) and its technological procedures (diagnosis of greenhouse-grown pot atoe plants after break of dormancy of tubers by gibberellic acid and diagnosis on tuber sprouts after rindite treatment) on reliability of the detection of PW in the progeny of primarily infected plants from f ield provocative conditions were assessed. Seven potato cultivars with different maturity and resistance to PVY were evaluated in four years with different level of infection pressure. After natural termination of vegetation period, two to three tubers from each plant were taken. The both diagnoses were in each date performed on the same tubers. EL ISA was conducted as described by Clark, Adams (1977) with minor modif ications (Dedic, 1985). Diagnostic kit purchased from Bioreba (Switzer land) was used throughout the experiments. Absorbance (A(405)) values were determined by a Dynatech spectrofotometer (MR 700) and reactions were rated as positive if they exceeded a threshold value equal to the mean absorbance of the healthy control plus three times its standard deviation, and were higher than 0.1 optical unit. In the year with low infection pressure (1987) only five tubers of all 476 tested cultivar s were infected, and this very low rate of infection was unsuitable fo r evaluation. In the years with severe infection pressure (1988, 1989) , the two diagnostic procedures were compared in the both dates and th e results are presented in Tabs I and II. In autumn period the overall accordance attained 83 to 85%, considering individual cultivars it wa s 70 to 96%. In spring period the overall accordance ranged from 82 to 87%, and the individual cultivars reached 62 to 97%. Significant and highly significant differences between the both procedures of sample p reparation and subsequent diagnosis were observed due to uneven transl ocation and localization of virus. These differences were consistent f or all the cultivars tested (statistically insignificant for cultivars Radka and Nora, which belong to more resistant ones). After artificia l break of dormancy by means of rindite treatment 1.8 to 2.3 times mor e infected tubers were detected. Uneven translocation of PVY into part icular tubers of potato plant after natural infection in field conditi ons was noted both in cultivars with higher resistance rating and in m ore susceptible ones. On average of all the cultivars tested, the over all accordance of diagnosis in parallel (sister) tubers attained 72 to 77% and ranged from 61 to 88% depending on the cultivars (Tab. III). The results are discussed with regard to the reliability of laboratory diagnosis of the PVY in the progeny of primarily infected potato plan ts.