ISHS Acta Horticulturae 705: V International Walnut Symposium
BARK CANKERS ON ENGLISH WALNUT: AN EMERGING DISEASE |
| Authors: | A. Mazzaglia, A. Fabi, A. Belisario, I. Librandi, G. Cefalo, L. Varvaro, N. Anselmi |
| Keywords: | Juglans regia, Brenneria nigrifluens, stem lesion, Nectria, Fusarium, Botryosphaeria, Paraphaeosphaeria |
| Abstract:
The changes in agricultural practices applied in English walnut orchards and the cultivation of this species in areas not particularly vocate have led to differences in disease occurrence and severity compared to the traditional picture. The occurrence of numerous cases of decline and death associated with collar and stem cankers seems to be the result of the interaction of biotic and abiotic factors succeeded in years. Isolations from fragments of bark and wood at the edge necrotic lesions gave as main result that 3 fungal species were mainly associated to this symptomathology: Botryosphaeria sp., Paraphaeosphaeria sp. (an. Coniothyrium sp.), and Nectria haematococca (an. Fusarium solani). Their identification was obtained on the basis of morphological traits and by comparison of ribosomal sequences (ITS and a portion of 18S) inside of international databases. All these fungi can be considered potential canker agents. The colonization of Fusarium solani could be due to its role of opportunistic parasite. Pathogenicity tests confirmed F. solani capable to induce necrosis of cambium and the first layers of wood, which spread from the collar up into the trunk. Also bacteria isolated from walnut tissues have shown features typical of Enterobacteriaceae. Further studies identified Brenneria nigrifluens, the bacterial agent of bark canker on walnut, constantly associated with lesions, together with other mainly saprophytic Enterobacteriaceae. The presence of both fungi and bacteria in walnut bark lesions can open new speculations on relationships among organisms in causing disease and a role in canker development could be hypothesized. | |
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