FOLDED COTYLEDON—A CONDITION IN HYBRID CABBAGE, BRASSICA OLERACEA L. CV. SURVIVOR, THAT AFFECTS THE DISTRIBUTION AND FEEDING RATE OF THE FLEA BEETLE, PHYLLOTRETA CRUCIFERAE GOEZE

Abstract

Morphological and physical characteristics of plants, such as trichomes (pubescence), surface waxes, silication, toughness, sclerotization, colour, and shape may affect herbivory by providing inhospitable surfaces or by eliciting altered host behaviour (review by Noms and Kogan 1980). Even slight variations in the morphological structure of plants may enhance their fitness and form the basis of resistance. Seedlings of the hybrid cabbage, Brassica oleraceae L. cv. Survivor, provide an intriguing opportunity to study within the same plant the influence of radically different cotyledon morphology on the feeding behaviour of the crucifer flea beetle, Phyllotreta cruciferae Goeze, because a high proportion of seedlings of this cultivar (>92%) have one folded cotyledon. The condition arises from a failure of the inner cotyledon of the embryo to open fully and assume a normal horizontal plane after germination. The outer cotyledon is invariably normal and both cotyledons appear to grow at about the same rate (unpublished data). The degree of folding varies from cotyledons that are only a few degrees from horizontal to those that are fully folded and 90° from horizontal. This study reports the distribution and feeding of P. cruciferae on the morphologically different cotyledons of B. oleraceae cv. Survivor.