ISHS Acta Horticulturae 193: XIII International Symposium on Fruit Tree Virus Diseases
EPIDEMIOLOGIES OF X-DISEASES IN CALIFORNIA, USA |
| Author: | A.H. Purcell |
| Abstract:
X-diseases of cherry and peach were studied from 1977 to 1984 in north-central California orchards relative to leafhopper activity and orchard management. Disease occurrence for 2 strains (PYLR and GV) of X-disease were significantly correlated with previous X-disease incidence, orchard location, and geographic area but not with indices of the activity of known X-disease vectors, weed control practices, or the proximity of other crops or natural vegetation with the following two exceptions. First, some (but not most) spread of GV strain could be related to the proximity of ornamental shrubs that support the leafhopper vector Fieberiella florii near cherry. Secondly, the proximity of pear orchards accounted for most of the variance of the distribution of the PYLR strain of X-disease in peach. Although pear psylla abundance was correlated with PYLR spread in subsequent years, tests of thousands of psylla as PYLR vectors failed to prove this insect capable of spreading X-disease. Quantitatively testing hypotheses concerning the epidemiology of systemic or "virus-like" pathogens of large perennials is made difficult by the very small infection rate sufficient to cause very substantial losses of trees in a few years. This difficulty is compounded in the case of X-disease by the large number of potential vector species and alternative plant hosts that could provide inoculum. | |
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