VIEW ARTICLE

Resistance

Ethylene Production by Excised Sapwood of Clonal Eastern Cottonwood and the Compartmentalization and Closure of Seasonal Wounds. Louis Shain, Department of Plant Pathology, University of Kentucky, Lexington, 40546-0091; Joseph B. Miller, Department of Plant Pathology, University of Kentucky, Lexington, 40546-0091. Phytopathology 78:1261-1265. Accepted for publication 11 February 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-1261.

Increment cores were removed from ramets of six clones of eastern cottonwood at 3-mo intervals starting either in November, at the beginning of the dormant season, or in May, at the beginning of the growing season. By offsetting the two wounding series by 6 mo, it was possible to separate the effect of wound age from the effect of season of wounding with regard to dynamic host responses and the fungi that colonize such wounds. Production of ethylene by these cores of outer sapwood was measured 1 (et₁) and 2 (et₂) days after their collection and incubation in sealed containers under standardized conditions. Methane, a product of methogenic bacteria, was measured 1 day after core collection. Observations on wound closure were made at 3-mo intervals. At the time of harvest, each tree had wounds 3, 6, 9, and 12 mo old. Discoloration associated with wounds initiated during the growing season was significantly less than that associated with wounds initiated during the dormant season regardless of wound age. Clones differed in their capacity to compartmentalize wounds. Ethylene production (et₁) by increment cores collected in February correlated best with the ranking of mean clonal discoloration. The seasonal course of et₁, but not et₂, across clones faithfully mirrored that expected for the physiological activity of sapwood; i.e., it increased significantly through February, November, August, and May. The ratios of basal (February) to maximal (May) rates of et₁ ranged from 2.7 to 5.6 for better compartmentalizing clones and from 1.4 to 1.7 for poorer compartmentalizing clones. It is suggested that ratios of et₁ may be used to rapidly screen for superior compartmentalizing genotypes, although additional studies are necessary to confirm or refute this hypothesis. Wounds largely closed during the 3-mo period from May to August. Clones differed significantly in their rate of closure. Those with higher et₂ in May tended to close more rapidly Wound closure and compartmentalization, however, were not significantly related, nor was methane emanation significantly related to either of these host responses. Season of wounding seemed more influential than age of wound with regard to fungal colonization. Fusarium solani was isolated significantly more frequently from wounds initiated during the growing season, whereas decay fungi were isolated significantly more frequently from wounds initiated during the dormant season, regardless of wound age.