RESISTANCE IN CUCUMIS-SATIVUS L TO TETRANYCHUS-URTICAE KOCH .5. RAISING THE RESISTANCE LEVEL BY THE EXPLOITATION OF TRANSGRESSION

After crossing partially resistant varieties some lines with a markedly higher resistance level were selected. This transgression for resistance indicates a polygenic inheritance of the resistance. On the most resistant F5 lines selected, oviposition was reduced by 50 to 60% and the economic damage threshold was reached 5 to 8 weeks later than in the susceptible control. The level of acceptance was not influenced by the selection. The selection of individual F2 plants was hampered by low heritabilities, whereas the heritabilities of F3- and subsequent line means were generally high enough. Selection for higher resistance levels was attended by an unintended increase in cucurbitacin content. This is explained by linkage of genes for resistance and bitterness rather than by identity of these genes. © 1979 H. Veenan zonen B.V.