Xanthomonas pruni . [Descriptions of Fungi and Bacteria

Abstract

Abstract A description is provided for Xanthomonas pruni . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Prunus amygdalus, P. armeniaca, P. avium, P. cerasus, P. davidiana, P. domestica, P. japonica, P. mume, P. persica, P. salicina and other species of Prunus (30: 48; Elliott, 31: 105, p. 114). DISEASE: Bacterial leaf spot on leaves, twigs and fruit of plum, peach, apricot and cherry; black spot of plum and peach; bacterial shot-hole of leaves. Previously referred to in earlier literature as bacterial canker of stone fruits, name now reserved for the disease caused by Pseudomonas morsprunorum and P. syringae . Shot-hole on the leaves of trees infected by X. pruni differs from that of fungal origin by the presence of bacterial ooze and in the shape of the leaf perforations which are generally irregular or elongated instead of round (35: 530). Atypical symptoms have been reported on peach leaves (19: 292). Symptoms on cherry fruit differ from those on peach and plum (14: 178). Branch cankers on peach are shallow and do not become perennial as on plum. On peach they were not observed to girdle the stem (10: 224). GEOGRAPHICAL DISTRIBUTION: Africa (Southern Rhodesia, South Africa); Asia (China, India, Japan, Korea, U.S.S.R.): Australasia (Australia, New Zealand), Europe (Cyprus, Italy, Romania); North America (Bermuda, Canada, U.S.A.): South America (Argentina, Brazil, Uruguay). In the U.S.A. the disease occurs on stone fruits in at least 26 States (30: 48; CMI Map 340, Ed. 2, 1964). TRANSMISSION: Xanthomonas pruni is disseminated by wind and rain (29: 218). The pathogen enters leaves through the stomata, and fruit infection appears to follow that of the leaves, probably as a result of leaf drop during rainy spells (7: 76). Primary leaf infection on peach originates in twigs with spring cankers (Thornberry & Anderson, 1933) or terminal die-back in which the pathogen overwinters (39: 600). Summer cankers on peach are only important under certain conditions for initiating spring infection (34: 732, 379), but on plum and apricot they play a more permanent role since the infection originating in the current season's twigs continues to develop in them during the following spring (Anderson, 1956). Overwintering on plum buds and fallen leaves has also been reported (41: 608). Species of Cicada may damage the bark of plum in New Zealand and thus provide points of entry (32: 322). The chief means of transmission of the pathogen in New Zealand is in budwood and root-stocks (42: 202).