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The Role of Twig Infections on the Incidence of Perennial Canker of Peach. Andrej Tekauz, Graduate Student, Department of Botany, University of Toronto, Ontario, Canada, Present title and address of senior author: Plant Pathologist, Canada Department of Agriculture, Research Station, Winnipeg, Manitoba; Z. A. Patrick, Professor Plant Pathology, Department of Botany, University of Toronto, Ontario, Canada. Phytopathology 64:683-688 . Accepted for publication 27 November 1973. DOI: 10.1094/Phyto-64-683.

An investigation of canker infections of 1-yr-old peach twigs revealed that Leucostoma cincta is the primary parasite causing that disease in the Niagara peach-growing region of Ontario, Canada. This species was isolated from 98.0% of the nodal twig infections sampled, while only 2.0% yielded cultures of L. persoonii. Autumn inoculations of simulated leaf scars with a conidial suspension of L. cincta resulted in nodal twig lesions, but inoculation of buds did not result in infection. Excision of leaves, buds, or both from twig nodes was carried out prior to the dormant season and the effect on natural infection was monitored. Twigs with nodes completely removed had seven times fewer infections than control twigs. The effect of leaf or bud removal on infection suggest that either site can act as an infection court during the dormant season. No differences were detected in the relative susceptibility of nodes on different parts of a twig to canker infection. Because the lowermost leaves on each twig tend to abcise first, the time available for leaf-scar healing prior to the onset of the dormant season differs on parts of the same twig. On 1-yr-old twigs the Leucostoma pathogens could be isolated up to 2 cm in advance of the macroscopically visible canker lesion. Microscopic examination revealed hyphae of the fungus in the pith, xylem, and cortical tissues of the infected twigs. Xylem vessel walls show browning in advance of the macroscopically visible lesion. Gum plugs in the vessel lumens are common. The progression of tissue discoloration in the twig suggests that the xylem tissues are invaded by the pathogen prior to those of the bark or cortex. Most perennial cankers have the remnants of a twig at their center. This suggests that such cankers are the result of twig infections that have spread to the subtending branch. The twig phase is thus of major importance in the peach canker disease complex.