ISHS Acta Horticulturae 472: XVII International Symposium Virus and Virus-Like Diseases of Temperate Fruit Crops
ELIMINATION OF APPLE FRUIT AND BARK DEFORMING AGENTS BY HEAT THERAPY |
| Authors: | W.E. Howell, J. Burgess, G.I. Mink, L.J. Skrzeczkowski, Y.P. Zhang |
| Keywords: | Malus domestica, apple viroids and viruses |
| Abstract:
Heat treatment followed by shoot tip grafting eliminated the agents of the following apple diseases from their apple (Malus domestica) cultivars: apple scar skin, apple dapple apple, flat apple, apple freckle scurf, apple false sting, apple rough skin, and three isolates of apple green crinkle. Budwood was collected from trees affected with these fruit and bark deforming diseases, propagated onto seedling rootstocks, and grown at 38°C for 70 days. Shoot tips (5 mm) were excised from these heat treated trees and cleft grafted onto green shoots on one-year-old apple seedlings. These propagants were then grown in field plots and observed for symptoms over a 5 to 7 year period. Except for trees from the scar skin and dapple apple sources, 100% of the plants produced after heat therapy were free of their respective diseases and also free from apple chlorotic leaf spot, apple stem pitting and apple stem grooving viruses that existed with the original cultures. Twenty to sixty percent of the trees produced from the apple scar skin and dapple apple sources assayed negative for apple scar skin viroid (ASSVd), the causal agent of these diseases. The ASSVd assays were conducted by biological tests on woody indicator hosts, by hybridization assays (annually), by RT-PCR and during the final three years of the trial by visual observations for fruit symptoms. Standard heat treatment combined with shoot-tip propagation is an effective method for obtaining trees free of the causal agents of these diseases for use in plant introduction and certification. | |
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