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John F. Wachter and Paul E. Cappiello

Stems of 38 varieties of Kalmia latifolia, 33 varieties of Viburnum, and 45 varieties of Magnolia were screened for low-temperature tolerance on eight dates during the winters of 1995–96 and 1996–97. Terminal 6- to 8-cm stem cuttings were shipped overnight on ice to Orono, Maine, and processed immediately upon arrival. Cuttings were subjected to a controlled freezing regime with a lowest test temperature ranging from –31°C to –42°C. Following freezing, stems were incubated for 5 to 14 days at 21°C and evaluated for injury. Lowest survival temperatures (LST) for each variety were estimated as the lowest temperature at which 100% of stems were undamaged. Varieties of Viburnum dentatum, V. lantana, V. opulus, and V. trilobum were rated as consistently very cold-tolerant, with LSTs of at least –36°C on all test dates. All V. plicatum var. tomentosum varieties showed inconsistent survival and LST estimations. Midwinter LST estimates in Kalmia latifolia showed 40% of the tested varieties remained undamaged at or below –36°C. Ten percent of K. latifolia varieties tested were damaged at –24°C or warmer, with the remaining varieties having LSTs somewhere between –24°C and –40°C. Varieties of Magnolia showed inconsistent survival with LSTs estimated for only 5% of those tested. Direct comparisons by variety, test date and source will be discussed with emphasis on consistent LST estimation. Varieties of K. latifolia, Viburnum, and Magnolia best suited for use in northern landscapes will also be discussed.

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Paul E. Cappiello and Gary J. Kling

Cornus sericea L. rooted cuttings were held in cold storage for 60 days and then transferred to a growth chamber in hydroponic culture. Roots and shoot tips were sampled during storage and through resumption of vegetative growth. Samples were analyzed for abscisic acid (ABA), indole-3-acetic acid (IAA), zeatin, zeatin riboside, glucose, fructose, sucrose, and starch. Budbreak was associated with increasing levels of the cytokinins and IAA, and decreasing levels of sucrose and starch in the shoot tips. Regeneration of new roots was preceded by an increase in the cytokinins and IAA, and a decrease in ABA in roots. Root sucrose increased nearly two times 1 week after budbreak and starch content generally decreased throughout the experiment. The results agree, in general, with previous reports indicating decreasing levels of ABA and increasing levels of cytokinins to be associated with root regeneration and budbreak. They also indicate that, of the four carbohydrates studied, sucrose levels changed most dramatically during the root regeneration and budbreak processes.

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Janine G. Haynes, John M. Smagula, and Paul E. Cappiello

Stem cuttings were harvested in April from four clones of containerized bunchberry(Cornus canadensis L.) forced in the greenhouse and in June from the same four clones growing in the field. April cuttings that had produced rhizomes by transplant time produced the greatest mean number and weight of shoots during the first growing season compared to April cuttings without rhizomes, June cuttings with rhizomes, or June cuttings without rhizomes. In a second study, cuttings and single-stem divisions were taken in July; divisions produced a greater mean number of shoots than did stem cuttings when compared at the end of Oct. A third study evaluated the effect of K-IBA application to lateral buds on subsequent rhizome production, and the effect of cutting node number (two vs. three nodes) on root or rhizome development. Treating lateral buds with K-IBA was not inhibitory to rhizome formation and elongation. Compared to two-node cuttings, three-node cuttings produced greater mean rootball size, rhizome number, and rhizome length; nearly twice as many of the three-node cuttings formed rhizomes as did two-node cuttings. A fourth study showed that cuttings rooted for 5 or 6 weeks in a mist enclosure generally exhibited greater shoot and rhizome production by the end of the first growing season than cuttings rooted for 8 or 9 weeks. This was despite the finding that cuttings rooted for longer durations (8 or 9 weeks) possessed larger rootballs and greater rhizome numbers at transplant time compared to cuttings rooted for shorter durations (5 to 6 weeks). Chemical name used: indole-3-butyric acid (K-IBA).

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Paul E. Cappiello, John F. Wachter, and B. Libby

Accurate assessment of the low-temperature tolerance of woody landscape plants is essential to ensure proper siting and use of specific varieties in the landscape. Laboratory determination of lowest survival temperature (LST) has become a popular area of study in recent years, yet there has been no standardization of technique among the many labs conducting this work. One of the major differences in technique employed across the country is the presence or absence of ice seeding of samples prior to the testing procedure. This presentation will present results of a series of studies conducted to determine the need for and efficacy of ice seeding treatments for LST determination in woody plants. A series of four studies was conducted over a 3-year period to test the difference in LST estimation with and without ice seeding. Twenty-two taxa, including both deciduous and evergreen species, were subjected to controlled freezing at ≈4°C/hr. with test samples removed from the freezer every 3°C. Following a 24-hr thaw and 5 to 7 days of incubation at 21°C, 100% RH, stems were sliced longitudinally and visually assessed for damage to vascular tissues. In the majority of cases, ice seeding was determined to have no significant affect on LST determination. In several species (Kalmia latifolia, Vaccinium angustifolium), the introduction of ice seeding into the protocol resulted in greater variation and less distinct determination of LST.