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 plant s of the pear rootstocks OH x F 51, OH x F 333, B 21, C 106 and D 50, and Adams quince were grown in low calcareous soil (LC, t.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% time content. By the end of Year 2, OH x F 5 1 , 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 lowe r soil-lime contents. Only Adams decreased the shoot-to-root dry weigh t ratio in relation to increased soil lime. Leaf chlorotic symptoms of plants grown under increasing lime were most severe in OH x F 333, D 50 and Adams. Root Ca concentration increased linearly and root iron a nd manganese decreased linearly at increasing soil lime rates. Root Cu concentration increased linearly with soil Cu content, the latter bei ng ten-fold higher in HC than LC soil. These findings indicate varying susceptibility of pear rootstocks to lime-induced iron chlorosis. Roo tstock tolerance is a necessary condition in order to overcome lime-in duced iron chlorosis in pear cultivars. In grafted trees it is, howeve r, possible that mechanisms other than iron uptake are involved in lea f chlorosis.