ISHS Acta Horticulturae 705: V International Walnut Symposium
PHYTOPHTHORA SPECIES ASSOCIATED WITH DECLINE AND DEATH OF ENGLISH WALNUT IN ITALY AND FRANCE |
| Authors: | A. Belisario, M. Maccaroni, A.M. Vettraino, A. Vannini, A. Valier |
| Keywords: | Walnut disease, Phytophthora, collar and root rot, soil disease, Juglans |
| Abstract:
Phytophthora species were consistently isolated from rot collars and roots, flame-shaped lesions on trunks, and from soil collected under declining trees in 16 English walnut plantations, 12 of which were located in Italy and 4 in south-western France. Six different Phytophthora species (P. cactorum, P. cambivora, P. cinnamomi, P. citricola, P. cryptogea, and P. nicotianae) were isolated and identified on the basis of morphological traits and on the RFLP patterns of the ITS region of rDNA. P. cinnamomi was the most widespread, being recovered from 11 sites. This species was consistently associated with declining and dead walnut trees. P. cactorum, P. cambivora and P. cinnamomi were among the species associated with necrotic tissues of the collar and main roots; dark, flame-shaped necroses, spreading up into the trunk, were often present on trees from which these species were isolated. P. cinnamomi was the most aggressive species in inoculations trials. It is likely that the incidence of Phytophthora decline and death of English walnut is underestimated as the disease often goes undetected as symptoms can be misinterpreted being very similar to those caused by drought or nutritional deficiency. As demonstrated for other broadleaves, a complex of Phytophthora species has been defined in association to English walnut decline. | |
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