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Pauliina Palonen and Leena Lindén

`Maurin Makea', `Muskoka', ` Ottawa', and `Preussen' red raspberry (Rubus idaeus L.) canes were collected from the field and subjected to different hot water treatments (20, 35, 40, 45, and 50 °C) to determine if endodormancy could be removed by a near lethal stress. Estimation of days for 50% budbreak (DD50) was found useful for describing the state of bud dormancy in the samples. Bud dormancy was broken in `Ottawa' by immersing the canes in 45 °C water for 2 hours, in `Maurin Makea' by treating the canes in 40 °C water, and in `Preussen' by both 40 and 45 °C treatments. The influence of this treatment on dormancy and cold hardiness at different times of the winter was further examined using `Ottawa' raspberry. The treatment removed bud dormancy most effectively in October, when the samples were in deepest dormancy. A slight effect was observed in November, but no effect in January. During ecodormancy in February the treatment delayed budbreak. Hot water treatment reduced cold hardiness of `Ottawa' canes by 8 to 15 °C, and that of buds by 9 to 13 °C during both endo- and ecodormancy. Based on the capacity of buds and canes to reacclimate, recovery from the stress treatment was possible at temperatures ≥4 °C. Loss of cold hardiness was caused by high treatment temperature itself and was not related to breaking of dormancy in samples. This finding suggests that dormancy and cold hardiness are physiologically unconnected in raspberry.

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Pauliina Palonen and Leena Lindén

Canes and flower buds of selected red raspberry cultivars (Rubus idaeus L. `Maurin Makea', `Muskoka', and `Ottawa') were sampled from a field (latitude, 61 °20'N; longitude, 24 °13'E) at 1-month intervals during Winter 1996-97 to study the interaction of dormancy and cold hardiness, hardiness retention, and rehardening capacity. One set of canes was subjected to dehardening (3 days) and two sets to dehardening + rehardening (3 and 7 days) treatments before cold hardiness determination. Maximum midwinter hardiness occurred in January, after breaking of endodormancy. Cold hardiness of canes and buds reached -28.6 to -37.2 °C and -24.2 to -31.6 °C, respectively. Throughout the winter, raspberry canes were hardier than buds. Endodormancy had a greater influence on dehardening and rehardening in buds than in canes, and cultivars differed in their response. Dehardening of `Maurin Makea' canes and buds, and `Muskoka' buds was slightly enhanced by breaking of dormancy, whereas dehardening in `Ottawa' was not affected by dormancy. Raspberry canes and buds could reharden even after dormancy release. Rehardening capacity was affected by the state of dormancy only in `Maurin Makea' buds. Changes in dormancy status failed to explain cultivar differences regarding dehardening and the capacity to reharden suggesting other factors may be involved.

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Leena Lindén, Pauliina Palonen, and Mikael Lindén

Seasonal cold hardiness of red raspberry (Rubus idaeus L.) canes was measured by freeze-induced electrolyte leakage test and visual rating of injury. Leakage data were transformed to percentage-adjusted injury values and related to lethal temperature by graphical interpolation and by the midpoint (T50) and inflection point (Tmax) estimates derived from three sigmoid (the logistic, Richards, and Gompertz) functions. Tmax estimates produced by Richards and Gompertz functions were corrected further using two different procedures. The 10 leakage-based hardiness indices, thus derived, were compared to lethal-temperature estimates based on visual rating. Graphical interpolation and Tmax of the logistic or T50 of the Gompertz function yielded lethal-temperature estimates closest to those obtained visually. Also, Tmax values of the Gompertz function were well correlated with visual hardiness indices. The Richards function yielded hardiness estimates deviating largely from visual rating. In addition, the Richards function displayed a considerable lack of fit in several data sets. The Gompertz function was preferred to the logistic one as it allows for asymmetry in leakage response. Percentage-adjusted injury data transformation facilitated curve-fitting and enabled calculation of T50 estimates.

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Leena Lindén, Hannu Rita, and Terhi Suojala

Logit models were used to analyze freeze-survival data of apple (Malus domestica Borkh.). The effects of hardening and dehardening treatments and two treatment durations on lethal temperature were studied using two cultivars. The major benefits of logit models were 1) the form of the sampling variation in the qualitative response variable was taken into account, 2) the lethal temperatures could be estimated with confidence intervals, and 3) the effects of treatments could be interpreted and compared easily using odds ratios. The momentary frost resistance estimates for `Antonovka' and `Samo' were –46 and –43C, respectively. Dehardening at 14C raised the lethal temperature by 12 to 15C, whereas hardening at –15C did not affect the frost resistance of either cultivar.

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Aino-Maija Evers, Leena Lindén, and Erja Rappe

Approaches using human issues in horticulture (HIH) offer new possibilities to develop nearby nature in cities, especially during a period of rapid urbanization in Finland. New initiatives have been developed in school gardening, environmental education, gardening in training programs for disabled people, therapeutic environments in hospitals and institutions, and in the University of Helsinki horticultural education and research programs. At the University of Helsinki, two contact teaching courses and national seminars were organized in 1996 and 1998. Initial studies in the HIH approach have three main themes: 1) gardening as a tool for better quality of life in homes for the elderly, 2) ecology, native plants and extensive maintenance in parks, and 3) the use of horticulture in environment and science education at the lower level of the comprehensive school.