Common cabbage resistance mechanisms against the diamondback moth: still an open book?

Despite the extensive research on host plant resistance of Brassica oleracea L. var. capitata (common cabbage) against Plutella xylostella L. (diamondback moth), knowledge of the resistance mechanisms involved remains incomplete. While robust evidence exists for the physical (antixenosis) mechanisms believed to cause resistance in glossy-leaved breeding lines, the one mechanism proposed in the literature to date (polar leaf extracts causing antibiosis) at best only explains a part of the resistance observed in two partially-resistant normal-bloom breeding lines in the field and the evidence is suggestive rather than direct.
Evidence from other host plant resistance studies involving P. xylostella is discussed and the other possible mechanisms are considered with the aim of providing a context for further investigations on host plant resistance mechanisms against P. xylostella.