Abstract
A description is provided for Didymella applanata. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Rubus idaeus (raspberry), R. fruticosus (blackberry) and R. ursinus var. loganobaccus (loganberry). Also on R. australis. DISEASE: Spur blight (in USA) and sometimes referred to as cane blight (in Europe). Early symptoms are purplish blotches mainly on the epidermis at the nodes round the base of leaves and sometimes between the nodes on the lower portions of the stems. As the disease progresses the blotches increase in size extending upward and downward along the cane and sometimes the lesions coalesce to form a discoloured cane. Didymella applanata has been reported to cause dieback (2, 457; 32, 572; 41, 353) and witches' brooms (2, 457). GEOGRAPHICAL DISTRIBUTION: Africa, Asia, Australasia & Oceania, Europe and North America (CMI Map 72, ed. 3, 1977). New records not mapped are: Europe (Czechoslovakia). TRANSMISSION: By ascospores and conidia released during wet or extremely moist conditions (10, 530; 55, 1875; Wormald, 1939; Converse, 1966). In the UK small numbers of ascospores have been trapped in raspberry plantations throughout the summer and early autumn when RH exceeded 70% and temperatures above 12°C prevailed for at least 12 h (37, 201). It invades both unwounded and wounded tissues (9, 117-118; 10, 531). Entry into canes is also achieved through wounds created by Diplosis (gall fly) in Germany (11, 381) and by Thomasiniana theebaldi (midge) (28, 340; 32, 86; 34, 728; 39, 120; 43, 519). As a rule the fungus invades all regions of the cortex except the cork which acts as a barrier (9, 117-118; 10, 531; 11, 381) but it has been known to cause deeper lesions on midge larval feeding areas and frequently penetrates the stem to the pith and kills the cane (32, 86).
Cane Blight of Rose Caused by Pestalotiopsis populi-nigrae(Sawada et Ito) Morelet.
