Growth and mineral nutrition of pear rootstocks in lime soils

Little information is available on the tolerance of pear rootstocks to lime-induced iron chlorosis. In a 2-year study, micropropagated plants of the pear rootstocks OH × F 51, OH × F 333, B 21, C 106 and D 50, and Adams quince were grown in low calcareous soil (LC, 1.6% lime) and high calcareous soil (HC, 72.9% lime) as well as in a mixture of HC:LC (50:50, w:w) (M1) at 33.8% lime content and a mixture of HC:LC (75:25, w:w) (M2) at 48.3% lime content. By the end of Year 2, OH × F 51, B 21 and C 106 had reduced dry matter accumulation in stem and roots in HC soil only; the other rootstocks were adversely affected by lower soil-lime contents. Only Adams decreased the shoot-to-root dry weight ratio in relation to increased soil lime. Leaf chlorotic symptoms of plants grown under increasing lime were most severe in OH × F 333, D 50 and Adams. Root Ca concentration increased linearly and root iron and manganese decreased linearly at increasing soil lime rates. Root Cu concentration increased linearly with soil Cu content, the latter being ten-fold higher in HC than LC soil. These findings indicate varying susceptibility of pear rootstocks to lime-induced iron chlorosis. Rootstock tolerance is a necessary condition in order to overcome lime-induced iron chlorosis in pear cultivars. In grafted trees it is, however, possible that mechanisms other than iron uptake are involved in leaf chlorosis.