Authors:S. Trdan, D. Znidarcic, E. Zlatic and J. Jerman and J. Jerman
In the period of 2001-2002 the susceptibility of five varieties of early white cabbage to onion thrips (Thrips tabaci) attack has been studied. The variety with the longest growth period (72 days) and the firmest head (19.5-21.5 kg/cm2), i.e. Vestri, had the highest mean weight of the head (1220.0 g/head) and the highest net weight of the head (1050.6 g/head), while the mean index of damage (1.18) and the mean yield loss (13.9%) were the lowest in this variety. At higher plant density (16.6 plants/m2) both parameters of the weight of the head were approximately less than half as compared to lower plant density (8.2 plants/m2). Results of the mean net weight of the heads did not show significant differences between different plant densities if the yield was calculated per area unit (m2). The mean content of epicuticular wax differs among varieties, although all varieties show similar relations in its content; the lowest mean content in the third and the fourth exterior leaves of the head, the highest mean content was within the first and the second, and the ninth and the tenth exterior leaves of the head. In spite of the apparent correlation between the content of epicuticular wax and the mean index of damage (with both plant densities its values were the highest between the third and the sixth exterior leaf of the head) caused by feeding of onion thrips hardly perceived negative correlation (Pearson coefficient of correlation between -0.338 and -0.436) were found between these two parameters using statistical analysis.
Authors:S. Trdan, N. Valič, L. Andjus, I. Vovk, M. Martelanc, B. Simonovska, J. Jerman, R. Vidrih, M. Vidrih and D. Žnidarčič
In a field experiment on the natural resistance of cabbage (
) against onion thrips
, 20 cabbage genotypes were included: 9 early, 5 mid-early, 6 mid-late (regarding the longevity of the growing period), 3 red, 17 white (regarding colour), 14 hybrids and 6 varieties (regarding genetic origin). For comparisons between genotypes, we determined significant differences in the mean index of damage on the exterior leaves of cabbage heads (1.12–2.83), the net weight of heads (281.40,151169.6 g), and yield loss (5.8–47.4%). The concentration of several compounds from cabbage leaves (epicuticular wax, α-amyrin, β-amyrin, lupeol, sucrose, glucose, fructose, vitamin C, palmitic acid, stearic acid, and arachidic acid) are measured. For all groups of cabbage genotypes the only confirmed negative correlation was between the extent of damage caused by the sucking of onion thrips and epicuticular wax content on the cabbage leaves (in groups where we artificially placed genotypes with similar characteristics). After this preliminary experiment, the research must be extended in order to determine the effect of the remaining analysed compounds in cabbage leaves for resistance (sensitivity) of cabbage to onion thrips attack.