Viruses and phytoplasma in European pear trees in New Zealand and the role of these pathogens in the compatibility of pear with quince rootstocks

Abstract

The history of European pear (Pyrus communis L.) cultivars, and pear and quince (Cydonia oblonga Mill.) rootstocks used in New Zealand during the present century was investigated in relation to their virus and phytoplasma disease status. Early attempts to control tree size and vigour using quince clonal rootstocks or seedlings of Oriental pear (P.pyrifolia Burm. Nak.) were unsuccessful, in part because of the presence of these diseases, and pear trees were grown for most of this century on European pear seedling rootstocks. Testing of 12 older pear cultivars commonly grown in commercial orchards at the present time showed that most were infected with several viruses, and also with the phytoplasma disease apple rubbery wood. All of the 12 cultivars were imported before, or at the beginning of this century, and were likely to have been infected in their country of origin before being introduced to New Zealand. When freed from infection by heat therapy, some were successfully grown on the virus‐free East Mailing rootstocks ‘Quince A’ and ‘C, and on the French rootstock ‘Quince BA 29’ without incompatibility problems, but others required an intermediate such as ‘Beurre Hardy’ to overcome non‐pathogen induced incompatibilities.