Leaf epicuticular wax, an antixenotic factor in Brassicaceae that affects the rate and pattern of feeding of flea beetles, Phyllotreta cruciferae (Goeze)

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Abstract
Crop brassicas with waxy leaves (> 1000 mg kg−1) were fed upon by flea beetles, Phyllotreta cruciferae (Goeze) (Coleoptera: Chrysomelidae), at a low rate, and feeding occurred predominantly at the edges of leaves. Species with non-waxy leaves (< 240 mg kg−1) were fed upon at a high rate, and feeding occurred randomly throughout the leaf. The regression of feeding rate upon amount of epicuticular wax had an R2 = 0.64, indicating that 64% of the feeding variation of flea beetles on diverse species and cultivars of Brassicaceae was explained by a single factor regression. Feeding studies on low-wax (eceriferum, cer) Brassica mutants confirmed that leaf epicuticular wax is an important antixenotic factor that affects the rate and pattern of feeding of flea beetles. The CC genome of B. oleraceae was identified as the source of the waxy-leaf character that gives rise to the low feeding rate and edge-feeding pattern of flea beetles. The digenomic amphidiploid B. napus (AACC genome), derived from the monogenomic diploids B. oleraceae (CC genome) and B. rapa (AA genome), and the digenomic amphidiploid B. carinata (BBCC genome), derived from monogenomic diploids B. oleraceae and B. nigra (BB genome), had waxy leaves and an edge-feeding pattern and rate similar to members of the B. oleraceae group. All other monogenomic diploids (AA, BB, DD, SS, RR) and digenomic amphidiploids (AABB) not possessing the CC genome had non-waxy leaves, a high rate of feeding and a random feeding pattern by flea beetles.Key words: Brassica, epicuticular wax, feeding, resistance, Phyllotreta cruciferae

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