Photosynthesis and assimilate transport in potato with top-roll disorder caused by the aphid Macrosiphum euphorbiae

In pot experiments in a glasshouse, top-roll symptoms were induced on potato plants after infestation with the aphid Macrosiphum euphorbiae. Leaves showing symptoms accumulated carbohydrates and tuber yields of affected plants were decreased by 44% compared with controls. Leaves grown after killing the aphids had a normal appearance and sugar contents. Infestation with aphids primarily inhibited carbohydrate transport in the stem and the accumulation of ¹⁴C-labelled assimilate in the vascular bundles of the leaves. It is suggested that photosynthesis is inhibited by impaired phloem transport and subsequent accumulation of carbohydrates in the leaves and not by direct mechanical damage caused by the feeding aphid.