1971
Authors
Louis ShainAbstract
Examination of freshly cut Norway spruce (Picea abies) during all seasons of the year revealed that an alkaline, light green to olive-colored reaction zone was present between sapwood and the brownish central core of wood decayed by Fomes annosus. The reaction zone, which contained dead, almost starch-free parenchyma, was formed in advance of the pathogen. Bacteria and nonhymenomycetous fungi were isolated occasionally from reaction zones, particularly in lower parts of stems where moisture content of this tissue frequently was high. Reaction zones darkened in color shortly after trees were felled. This color change was dependent upon oxygen, and it appeared to be mediated by oxidative enzymes produced by the host. Reaction zone formation was attributed to a nonspecific response to injury or infection during necrosis of parenchyma. The reaction zone contained more extractives than adjacent tissues, particularly phenols with ultraviolet absorption spectra typical of lignans. Reaction zone and incipiently decayed wood contained more potassium, calcium, and magnesium than sound sapwood or heartwood. Expressed sap from the reaction zone had a fungistatic effect on F. annosus; this could not be wholly explained by the high pH of this extract (about pH 8.0). Reaction zone and incipiently decayed wood were significantly more resistant to decay than sound heartwood and sapwood. Spruce oleoresin and one of its components, abietic acid, inhibited linear growth of F. annosus in vitro. Results support the hypothesis that insufficient quantities of inhibitory substances in heartwood contribute to the susceptibility of spruce to extensive central stem rot, whereas limited invasion of sapwood is due to accumulation of inhibitory substances in a reaction zone.
Authors
Erik ChristiansenAbstract
No abstract has been registered
1970
Authors
Øystein AustaråAbstract
Includes, inter alia: a list of the recorded hosts (conifers and broadleaved species) and localities of G. podocarpi in E. Africa; data on the relation of late-instar larval density to degree of defoliation; and natural control, especially by a virus disease and laboratory tests of three insecticides against late-instar larvae.
Authors
Øystein Austarå T. JonesAbstract
No abstract has been registered
Authors
Øystein AustaråAbstract
No abstract has been registered
Authors
Kåre Olav VennAbstract
Reviews records of the occurrence of terminal dieback in P. sylvestris in Norway from 1863, and describes the symptoms and distribution of damage occurring in 1963. Sample trees ca. 0.5-2.0 m. high from 50 localities in which damage had occurred, and meteorological records for these areas, were studied. In view of the apparent connexion with summer frosts, special attention was paid to the development of annual rings and the occurrence of frost rings in the late wood. Results indicated that for every summer in which damage occurred there had been a short growing season with very low mean temperatures, and this had generally been preceded by a favourable summer in the previous year. These conditions appear to lead to insufficient development of the shoots, which do not acquire their normal frost hardiness. Such predisposed shoots may be injured by frost during the following dormant period or, as probably happened in 1963, by unfavourable early spring weather.
Authors
Øystein AustaråAbstract
In a further study to assist in estimating the profitability of insect control measures [cf. F.A. 30 No. 6021], 2-year-old Pinus patula plants were artificially defoliated in the rainy and the dry seasons at localities in Kenya, Uganda and Tanzania. Complete defoliation caused a reduction in height and diameter growth of ca. 50% for the year in question. With a few exceptions, ca. 50% defoliation, removing either (a) the youngest, or (b) the oldest foliage, did not significantly reduce growth, nor were there significant differences between (a) and (b). Trees defoliated at the start of the dry season recovered more slowly and showed a greater loss of growth than those defoliated at the end of the dry, or during the rainy season. Growth reduction by short-term 50% defoliation would seem to be economically tolerable, in that measures to prevent it would be uneconomic.
Authors
Sverre SkoklefaldAbstract
No abstract has been registered
Authors
A.L. FallasAbstract
No abstract has been registered
1969
Authors
Bjørn TveiteAbstract
No abstract has been registered