The role of plant characteristics in the resistance of white cabbage to onion thrips: preliminary results

The onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae) has been recognized as a severe worldwide pest of white cabbage (Brassica oleracea L. convar. capitata provar. capitata Duch.) for almost three decades. Although the most effective control measure is the use of resistant varieties, little is known about the resistance mechanism(s) involved. In 2007, a study at Tordas, Hungary, was carried out with 6 varieties to confirm that antixenosis is at least partly responsible for the resistance against onion thrips. The number of adult thrips and their progeny was counted on the outer ten head leaves at one-third of the heading process.At the same time, the light reflectance of old and outer head leaves was measured. The onion thrips damage was also assessed at full maturity. Antixenosis was found to be responsible for the resistance of ‘Balashi’, ‘Bloktor’ and ‘Riana’ varieties, since the number of adults and offspring found on head leaves was significantly lower than that of ‘Green gem’, ‘Hurricane’ and ‘Quisto’. The resistant varieties (‘Balashi’, ‘Bloktor’ and ‘Riana’) similarly suffered significantly lower damage than the susceptible ones (‘Green gem’, ‘Hurricane’ and ‘Quisto’). The light reflectance spectra of all six varieties were almost identical in the case of the old leaves, but a difference was found between the susceptible and resistant varieties when the reflectance of the outer head-forming leaves was measured. Similarly, the colour of the old leaves was not greatly different, but that of the outer head-forming leaves was correlated to the number of thrips adults found in the cabbage heads