In recent years, in Great Britain and countries situated along the coastal fringe of Northwestern Europe, "top-dying" has become the most destructive disease of Norway spruce (Picea abies (L.) Karst.). The disease affects healthy trees in the dormant period during years characterized by mild, windy winters (March included). The first effect to appear on trees in the interior of thinned plantations is reduction of height growth which may be followed by foliage loss. It is thought that this pattern is also followed by edge trees. When dry flay to August periods follow such winters the growth reduction is steep, anddeterioration of the health status of affected trees is speeded up. Occurrence of severe outbreaks of the disease may result when weather such as the above takes place for more than two consecutive years. The present outbreak in N.E. Scotland is regarded as commencing in 1971t thereafter continuously developing due to unusually mild windy winters accompanied by dry summers (May included) during the period 1971-75. Data for wind duration, air temperature and rainfall for the years 1961-75 were used as variables and annual height increments from three repeat stands were used as the dependent variable in a stepwise multiple regression analysis. Significant correlations with height growth, which precedes needle-browning, were always found for edge trees of stands and occasionally for trees inside stands. Trees, once affected by the disease, go through four distinguishable stages of deteriorating health until they die. These stages can be recognized by the significantly different amounts of needle loss. During the "top-dying" annual cycles-1971-75 and 1975-76 needle-browning in all tree-health categories started building up in mid, late winter-spring and culminated just before and in the early flushing period. Sudden, sharp increase of the rate of needle-browning was found to be closely associated with short spells characterized by clear sunny, warm weather accompanied by high velocity wind and low or even freezing temperature at night, occurring in the dormant period. Needle-browning was successfully prevented by bagging shoots from the early flushing period until late August. Tip needles of current and second year were found to retain a significantly lower water content than base needles (expressed on needle dry weight) as did needles from bare 1 shoots compared withbaggedones during the period January-May. Water uptake by roots of Norway spruce plants, four years of age was significantly lower when cold water was supplied. Uptake at l u was found to be only 49.51% of that at 20G. Close observations and a number of experiments failed to show that R. kalkhoffii Bubak or any other needle fungus has a primary involvement in "top-dying". Similarly, no fungus likely to be strongly pathogenic to Norway spruce was isolated from various tissues of current and second year shoots. Strong evidence suggested that the fungus R. kalkhoffii isolated from Norway spruce and dealt with in this work is a different strain from those isolated in the U.S.A. and Japan from other host species. Its optimum temperature for diameter growth on malt agar was 18C. Malt agar pH's ranging from 3.5 to 9 (before autoclaving) did not have any significant effect on growth. It was shown to be a very successful colonizer of dying needles during its infection period which in 1976-77 started building up in August, culminated in October and stopped in late February. The hypothesis was developed that "top-dying" is caused by severe water stress created by adverse climatic conditions, chiefly mild, windy weather during the dormant period enforced by drought in the first part of the growing season. When conditions such as these occur for more than two consecutive years severe outbreaks of the disease may occur. In a test of this hypothesis, one young Norway spruce plant out of two tested, exhibited in vitro symptoms very similar to those recorded in the field after a 75 hr, exposure period under conditions consisting of air temperature 14C, relative humidity 70% and photoperiod of 12 hrs.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:453577 |
| Date | January 1977 |
| Creators | Diamandis, Stephanos |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU447008 |
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