Effects of simulated and flea beetle injury to cotyledons on growth of drought-stressed oilseed rape, Brassica napus L.

Abstract

Simulated injury was compared with flea beetle injury on cotyledons of oilseed rape grown at various soil moistures to determine the effects of injury on seedling growth in the greenhouse. The cotyledons of 7-d-old seedlings were injured at 0, 25, 50, and 75% of the total area with a 0.5-mm mechanical pencil or by flea beetles. The soil moisture was maintained at the field capacity, half field capacity, and the permanent wilting point. The growth response of the seedlings was compared for simulated flea beetle injury and soil moisture 7, 14, and 21 d post-injury, and for simulated and flea beetle injury, and soil moisture 7 d post-injury. Simulated injury had the greatest effect on seedlings grown at the field capacity, at 7 d post-injury. At the reduced soil moistures, increased levels of simulated injury were necessary to cause a significant loss in growth. By 14 and 21 d post-injury, compensation to the simulated injury occurred. Simulated injury caused significantly less growth reduction across all injury levels compared with flea beetle injury. However, at injury levels above 25%, both simulated and flea beetle injury had similar trends in growth reduction. The simulated injury tested in these experiments cannot be used in place of flea beetles for resistance screening studies, but may be useful if incorporated as a preliminary tool. Key words: Phyllotreta cruciferae, canola, oilseed rape, injury, damage response