ISHS Acta Horticulturae 472: XVII International Symposium Virus and Virus-Like Diseases of Temperate Fruit Crops
PEAR DECLINE RESISTANCE IN PYRUS COMMUNIS ROOTSTOCKS AND PROGENIES OF WILD AND ORNAMENTAL PYRUS TAXA |
| Authors: | E. Seemüller, K.-H. Lorenz, U. Lauer |
| Abstract:
Six OHF clonal rootstocks, rooted cuttings of four Pyrus species, and progenies of 36 Pyrus genotypes were examined for resistance to the pear decline phytoplasma following experimental inoculation. Evaluation of pear trees grown on these rootstocks revealed that none of the genotypes and progenies examined shows satisfactory PD resistance. However, considerable differences in susceptibility were observed among both the vegetatively propagated stocks and seedling progenies. Among the OHF stocks, clone 87 was little affected, whereas clones 18, 267, and 333 proved moderately susceptible and clones 69 and 217 were highly susceptible. Similar differences were observed among the seedling progenies. In all of them were individuals which never developed symptoms or which showed only temporarily light symptoms and then recovered. However, the number of plants which was not, slightly, moderately or severly affected differed greatly among the progenies so that the material could be classified into three resistance groups. Least affected were progenies of P. nivalis, P. calleryana var.tomentella, P. communis, P. betulifolia, P. x michauxii, P. amygdaliformis, P. kunoriana, P. ussuriensis, and P. cuneata. However, in some of these taxa, considerable differences between progenies of different genotypes were observed. So, the progenies of certain genotypes of P. betulifolia, P. communis, P. nivalis, and P. ussuriensis were severely affected and had to be classified with the most susceptible taxa such as P. pyrifolia, P. gharbiana, P. x lecontei, and P. bretschneideri. Work to detect phytoplasmas in inoculated trees using the DAPI test and PCR revealed that most inoculated trees remained infected until the end of the observation period. However, presence or nondetectability of phytoplasmas were not clearly correlated with resistance parameters such as development and severity of symptoms or recovery. | |
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