ISHS Acta Horticulturae 94: XI International Symposium on Fruit Tree Virus Diseases
ETIOLOGY AND NATURAL SPREAD OF BLACKLINE DISEASE OF ENGLISH WALNUT TREES |
| Authors: | S.M. MIRCETICH, G.A. DEZOETEN, J.A. LAURITIS |
| Abstract:
Blackline (BL) disease of English walnut trees (Juglans regia) is widely distributed and causes serious losses in trees, propagated on J. hindsii or Paradox rootstock (J. hindsiix J. regia), in several walnut-growing regions of California. The blackline causal agent was readily graft-transmitted by bark patches from naturally infected walnut trees into healthy walnuts. Necrosis (blackline) of cambium and phloem at the union between J. regia and J. hindsii, resembling that in naturally infected trees, developed in the inoculated walnuts within 8–12 months after inoculation. A virus was recovered from naturally and experimentally BL-infected walnut trees. The virus particles are isometric, about 26 nm in diameter and in thin sections show characteristics of a NEPO virus. Natural spread of BL was demonstrated by annual surveys of commercial walnut orchards. Typically, the disease spread from infected to adjacent healthy trees. No random occurrence of newly infected trees in the orchards was observed. The relation of BL virus to BL disease in walnuts is discussed. | |
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