INTRODUCTION

Screening for resistance to virus diseases based on both qualitative and quantitative measurements of virus in plants grown under controlled conditions may increase the efficiency of resistance breeding. Moreover, a measurement of changes in virus content in host plants could be of great help in studying the nature of resistance. It has been suggested that the enzyme-linked immunosorbent assay (ELISA) is a suitable technique for the assessment of virus content and a negative correlation between the extinction values in ELISA and the level of resistance to PVYN in some potato varieties has been found. However the assessment may be influenced by a number of factors. This paper describes the results of an investigation on the effect of time interval between inoculation and assessment on the relative content of virus in leaves of plants infected with PVYN.

MATERIALS AND METHODS

Three experiments were carried out in 1984 and 1985 at the Foundation for Agricultural Plant Breeding (SVP) in Wageningen. Plants grown in a glasshouse at 22 to 24°C and a daily photoperiod of 16h were inoculated mechanically at different plant ages and assessed for relative virus content by ELISA at different time intervals after inoculation. Leaves of inoculated plants were sampled at different positions according to an appropriate experimental design. ELISA was done according to the method of Clark and Adams (1977) with the modification of De Bokx and Maat (1979). The varieties used in the experiments differed in resistance to PVYN (Anon. 1985).