Anders Lindström

Cold Acclimation and Deacclimation of Shoots and Roots of Conifer Seedlings

Conifers that are adapted to grow in regions where marked annual temperature changes are observed have developed physiological mechanisms that enable them to alternate their growth and rest periods in phase with the climate, so they exhibit a strong periodicity in cold hardiness. Cold acclimation is the transition from a non-hardy state to a hardy one. It is a complex physiological process that enables plant tissues to become tolerant to extracellular freezing, duration of cold and also to temporal thawing (Levitt 1980). The annual growth rhythm of trees and the ability to cold harden are determined genetically (Weiser 1970) but are controlled by environmental cues (Levitt 1980).

Root deformation in plantations of container-grown Scots pine trees: effects on root growth, tree stability and stem straightness

Root system deformation was studied in 23 Scots pine (Pinus sylvestris L.) stands in central Sweden. The study comprised both plantations created with container-grown plants (Paperpot) and natural stands including young (7–9 year old) and older (19–24 year old) trees. Trees were measured with regards to distribution of roots, root deformation, stability, stem straightness and wood properties in stumps. Root distribution was most uniform for naturally regenerated trees. Older trees generally showed a better root distribution than young trees. The young planted trees displayed a high frequency of severely spiralled root systems, while only a few of the older trees had spiralled root systems. No severe root deformations were observed on naturally regenerated trees. Naturally regenerated trees were more stable than those which had been planted. Differences in bending moment, when trees were pulled to an angle of 10°, were considerable between young planted and naturally regenerated trees, but less pronounced for the older trees. Young planted trees had the highest frequency of severely crooked stem bases, while naturally regenerated trees had the straightest mode of growth. Tensile strength in peripheral wood samples of the stumps was substantially lower for planted than for naturally regenerated trees. Strain values to breakage of wood samples, taken from the root collar and the central- and peripheral part of the stump were lower for planted trees. The conclusions from this study are that root distribution, tree stability and stem straightness of planted Paperpot-grown trees will improve after a certain time and approach the state of naturally regenerated trees. As trees grow older, early established crooked stem bases will be compensated by radial growth and the tree will appear straighter. Inside the stem, however, problems may still remain with abnormal fibre direction and compression wood together with inferior root strength due to fibre disturbances as a result of spiralled roots.

The distribution of Paenibacillus larvae spores in adult bees and honey and larval mortality, following the addition of American foulbrood diseased brood or spore-contaminated honey in honey bee (Apis mellifera) colonies

Within colony transmission of Paenibacillus larvae spores was studied by giving spore-contaminated honey comb or comb containing 100 larvae killed by American foulbrood to five experimental colonies respectively. We registered the impact of the two treatments on P. larvae spore loads in adult bees and honey and on larval mortality by culturing for spores in samples of adult bees and honey, respectively, and by measuring larval survival. The results demonstrate a direct effect of treatment on spore levels in adult bees and honey as well as on larval mortality. Colonies treated with dead larvae showed immediate high spore levels in adult bee samples, while the colonies treated with contaminated honey showed a comparable spore load but the effect was delayed until the bees started to utilize the honey at the end of the flight season. During the winter there was a build up of spores in the adult bees, which may increase the risk for infection in spring. The results confirm that contaminated honey can act as an environmental reservoir of P. larvae spores and suggest that less spores may be needed in honey, compared to in diseased brood, to produce clinically diseased colonies. The spore load in adult bee samples was significantly related to larval mortality but the spore load of honey samples was not.

Horizontal transmission of Paenibacillus larvae spores between honey bee (Apis mellifera) colonies through robbing

Surprisingly little is known about transmission rates between honey bee colonies of Paenibacillus larvae, the causative agent American foulbrood. We studied the rate of horizontal transmission of P. larvae spores between colonies as a function of physical distance between colonies by culturing for the spores from sequential samples of adult bees. The results demonstrate a direct effect of distance to clinically diseased colonies on the probability of contracting high spore levels, as well as on the probability of developing clinically visible disease symptoms. The results also demonstrate that colonies may develop considerable spore densities on adult bees without exhibiting visible symptoms of disease. Furthermore, the data suggest that transmission of AFB between apiaries occur within 1 km distance from clinically diseased colonies, but is significantly lower at 2 km distance or longer when colonies dead from AFB are allowed to be robbed out.ZusammenfassungZiel dieser Untersuchung war die Ermittlung der Entfernung, über welche Räuberei als Übertragungsweg von Paenibacillus larvae Sporen effektiv sein kann. Vierzehn Völker wurden in Entfernungen von 0, 0,5, 1, 2 und 3 km von dem Zielbienenstand aufgestellt, der drei Völker mit schweren AFB Infektionen enthielt. Die kranken Völker wurden im Herbst des ersten Experimentaljahres beräubert, starben im Winter und wurden im Frühjahr des zweiten Experimentaljahres erneut beräubert. Drei neue, hoch infizierte Völker wurden auf den gleichen Bienenstand gebracht. Sie wurden im Herbst beräubert, starben über den Winter und ihre verbliebenen Honigvorräte wurden im Frühjahr des dritten Experimentaljahres ausgeräubert. Als Proben wurden Adultbienen genommen und entsprechend den Standardprotokollen auf P. larvae Sporen hin kultiviert.Die Ergebnisse zeigen, dass Völker sich bis zu einem km Entfernung von dem Zielbienenstand an der Räuberei beteiligten (Abb. 1, Tab. I). Alle Völker auf diesen Bienenständen bis auf eins entwickelten klinische Krankheitssymptome. Hierdurch ist klar gezeigt, dass die Übertragung von Sporen durch die Räuberei auf kurze Entfernungen einen sehr wichtigen Übertragungsweg für P. larvae Sporen zwischen Bienenvölkern darstellt, und dass weiterhin die Übertragung von für die Entwicklung eines klinischen Krankheitsbildes ausreichenden Sporenanzahlen direkt mit der Entfernung von an AFB erkrankten Bienenvölkern zusammenhängt.Die Bienenstände in 2 und 3 km Entfernung zeigten keinen zeitlichen Trend, wiesen allerdings bei einigen Proben in unregelmäßigen Zeitabständen leicht erhöhte Sporenlevel auf. Sie entwickelten allerdings keinerlei klinische Symptome. Es ist bekannt, dass Völker über mehrere Jahre niedrige Sporenbelastungen aufweisen können, ohne jemals klinische Symptome der Krankheit zu entwickeln. Weitere Ergebnisse zeigten, dass die Zeit der Probennahme einen starken Einfluss auf die Gesamtentwicklung von Sporenbelastungen auf den Bienenständen hat (Tab. II). Weiter zeigte sich ein Interaktionseffekt zwischen dem Probenzeitpunkt und dem Bienenstand, was darauf hinweist, dass sich die Sporenbelastungen in den Bienenständen unterschiedlich über die Zeit entwickeln (Abb. 1, Tab. II). Die logische Schlussfolgerung dieses Ergebnisses ist, dass die Sporenladungen der adulten Bienen nicht nur auf das Räubereiereignis zurückzuführen sind, sondern weiterhin die Honigvorräte als Reservoir für die Sporen dienen und diese in die Kolonie freisetzen, wenn der Honig genutzt wird.

Sampling of adult bees for detection of American foulbrood (Paenibacillus larvae subsp. larvae) spores in honey bee (Apis mellifera) colonies

SUMMARY Fifty-nine apiaries with a total of 489 honey bee colonies belonging to a beekeeping operation in central Sweden with a previous history of American foulbrood (AFB) were inspected. For each colony the clinical disease status was visually inspected and the number of brood cells clinically diseased by AFB estimated. From 94 of these colonies, individual samples of > 100 live honey bees from the brood chamber and supers were collected. Two composite samples consisting of > 100 adult bees from each individual colony in each inspected apiary were also taken from (1) all brood chambers and (2) all supers, respectively. Samples were taken on both the individual colony level and the apiary level and analysed for presence of Paenibacillus larvae subsp. larvae by culturing. Spores were found in 100% (n = 21) of the bee samples from clinically diseased colonies and in 77% of the supers, and 82% of the brood chambers in colonies without clinical symptoms (n = 73). On the apiary level, 100% of the samples from clinically diseased apiaries were positive (n = 32). In the apiaries that showed no clinical disease, 70% of the composite samples from supers and 67% of the samples from brood chambers were positive for AFB (n = 27). Spore load differed only slightly between bees in brood chambers and in supers, suggesting that sampling bees from supers when screening apiaries for AFB is a fast and satisfactory alternative to sampling brood chambers.

Freezing temperatures in the root zone—effects on growth of containerized Pinus sylvestris and Picea abies seedlings

Roots of 1‐year‐old containerized seedlings of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) were experimentally frozen in December. The seedlings were then grown for 3 weeks in a growth chamber and evaluated with regard to root growth capacity (RGC) and shoot elongation. The subsequent RGC of Scots pine declined as root zone temperatures were lowered from ‐6°C to ‐11°C and from ‐11°C to ‐16°C. Almost no root growth was observed after exposure to ‐20°C. Shoot growth was also negatively affected by low root temperatures but less than root growth. Low root temperatures did not affect Norway spruce as much as Scots pine, although root and shoot growth of Norway spruce were reduced after exposure to the lowest test temperatures (‐16°C and ‐20°C). The length of exposure, ranging between 1 and 8 hours had no effect on subsequent growth.

Field Performance of a Protective Collar against Damage by Hylobius abietis

The effectiveness of a plastic collar designed to protect planted seedlings against damage caused by Hylobius abietis (L.) (Col., Curculionidae) was evaluated at 63 planting sites in southern Sweden during 1979 and 1980. Nearly 10 000 collar‐protected pine and spruce plants and 10 000 controls were carefully examined for Hylobius‐damage and other injuries. In addition, the impact of some microsite factors on weevil damage and collar performance was evaluated, and the height growth was measured. The protective effect of the collar for two seasons after planting was comparable to that of insecticides and was best at sites with sparse vegetation and high weevil pressure. Proper application of the collar was crucial for good control. Collars were not observed to affect plant growth. Soil scarification reduced mortality in both collared plants and controls.

Influence of soil temperature on root freezing tolerance of Scots pine (Pinus sylvestris L.) seedlings

The influence of soil temperature on the root freezing tolerance of one-year-old containerized Scots pine (Pinus sylvestris L.) seedlings was investigated. In addition, the TTC and electrolyte leakage methods were evaluated in terms of their suitability for use in detecting damage to roots caused by freezing. In mid-August, seedlings were placed in three thermostat-controlled soil beds in a greenhouse with an initial soil temperature of 14.3 °C. Soil temperature was lowered in two of the soil beds, resulting in temperatures of 10.7 and 5.3 °C respectively. Each soil temperature, i.e. 14.3, 10.7 and 5.3 °C was maintained for eight weeks. Starting in early September, damage to roots induced by artificial freezing was estimated biweekly by measuring electrolyte leakage, triphenyl tetrazolium chloride (TTC) reduction and potential root growth in a three-week cultivation test. In addition, the root freezing tolerance of seedlings placed outdoors was tested. Measurements showed that these seedlings were exposed to soil temperatures ranging from 13.0 °C in mid-August to 0.5 °C in November. Generally, the development of root freezing tolerance was more pronounced for seedlings exposed to lower (0.5 and 5.3 °C) soil temperatures compared with those exposed to higher (10.7 and 14.3 °C) ones. Root freezing tolerance was highest among the seedlings placed outdoors which were also exposed to the lowest soil temperatures registered in the study. To examine the effect of a temporary warm period, the soil temperature in one treatment was increased from 5.4 °C to 13.9 °C, maintained at the latter temperature for two weeks in October and then lowered to 5.7 °C. Root freezing tolerance was reduced by exposure to the warmer soil temperature. However, after four weeks at the colder soil temperature, the tolerance of the seedlings had returned to the level measured prior to exposure to the warm soil temperature. Methods based on the measurement of root electrolyte leakage and TTC reduction were both found to have limitations when used to detect root freezing damages in containerized seedlings.

Equipment for freezing roots and its use to test cold resistance of young and mature roots of Picea abies seedlings

Equipment for testing root cold hardiness of containerized forest tree seedlings is described in the paper. Using this equipment roots of containerized one‐year‐old Norway spruce seedlings were experimentally frozen on December 3. After freezing, lateral roots were divided and cut into young and mature parts. Samples of young and mature roots were then tested for vitality using the triphenyl tetrazolium chloride (TTC) method. In contrast to mature roots, the reduction of TTC decreased as younger roots were exposed to the lowest test temperatures of — 15°C and —20°C, indicating increasing root damage.

Outdoor winter storage of container stock on raised pallets—effects on root zone temperatures and seedling growth

Containerized seedlings of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) were overwintered on the ground and above ground on pallets. Soil temperatures in elevated containers were lower and showed greater fluctuation than containers on the ground. The lowest temperatures (‐15 to ‐16°C) were observed in containers stored on pallets with little or no snow cover during the winter. Temperatures in the edge rows of containers were lower than interior bed soil temperatures. Lower temperatures were also observed in the top than in the bottom of the container. The storage on pallets resulted in reduced shoot and root growth. Although insulation preventing air movements beneath the container units improved soil temperature conditions and subsequent seedling growth, the best result was obtained when seedlings were stored directly on the ground surface.