A. Belisario, M. Are, C.S. Palangio, S.O. Cacciola, G. Magnano di San Lio
Phytophthora cactorum (Leb. and Cohn) Schröet. (1886) is known as the agent of damping-off, crown and root rot on a wide range of host plants, including walnut. The fungus was already recorded as P. omnivora by de Bary in 1881. The disease was recorded as collar and root rot on several Juglans species namely J. californica S. Wats., J. hindsii (Jesp) Rehder, J. regiaL., J. nigra L. (Anonymous, 1923; ibidem, 1925; ibidem, 1927; ibidem, 1927; ibidem, 1928; Smith and Barrett, 1930 and 1931), since the first decades of the century in USA.

In Italy P. cactorum was reported as a pathogen in English walnut by Cristinzio and Vernau (1954) in the Campania region (Southern Italy). Since this first record the walnut collar rot has never been recorded again.

Since 1993 a collar rot of 1-and 2-yr-old potted seedlings of English (Persian) walnut (Juglans regia L.) has been observed in Central Italy. The disease appeared as black depressed, humid cankers of the bark, girdling the basal stem and inducing a progressive decline and death of the seedlings. Dying seedlings were more frequent in poorly drained soil or in areas which were excessively irrigated.

Phytophthora cactorum was consistently isolated from basal stem tissues of diseased seedlings. The isolates were identified on the basis of morphological and cultural characteristics. Moreover, electrophoretic analysis of total native proteins and isozymes (arylesterase, malate dehydrogenase, acid and alcaline phosphatases) gave banding patterns identical or very similar to those of P. cactorum isolates from various geographical origin and different hosts including apple, loquat, pineapple guava and strawberry.

In pathogenicity tests P. cactorum walnut isolate proved to be highly pathogenic to 1-yr-old potted seedlings of English walnut, causing the same symptoms originally observed.

Artificial inoculations were performed on 1-year-old English walnut seedlings by inserting at the collar bark a 5-mm-diameter mycelium plug cut from the active margin of 4 day-old cultures grown on potato-dextrose-agar (PDA), in the dark. Wounds were sealed with adhesive tape. Control plants were inoculated with PDA plug only. Symptoms appeared 7 days after inoculation and they were identical to those observed in nature.

Belisario, A., Are, M., Palangio, C.S., Cacciola, S.O. and Magnano di San Lio, G. (1997). COLLAR ROT OF WALNUT SEEDLINGS IN ITALY. Acta Hortic. 442, 389-392
DOI: 10.17660/ActaHortic.1997.442.62

Acta Horticulturae