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Dogwood (Cornus sericea L.) clonal ecotypes from northern latitudes (Northwest Territories “NWT”) and more southern latitudes (Massachusetts, Utah, and Chalk River, Ont.) were allowed to acclimate naturally in a shade house (52°07') beginning in early July and continuing through the middle of October. The NWT ecotype began to attain vegetative maturity by the second week of September, whereas the southern ecotypes did not attain any significant degree of VM before the first lethal frost.

Defoliation tests in controlled environment chambers paralleled shade house results. Under VM-inducing conditions (20/15°C, 8h), NWT ecotype attained VM after 40-50 days. Conversely, after 80 days Utah ecotype had not attained full VM.

Chilling requirement will be compared among ecotypes and ABA levels will be quantified using HPLC and ELISA systems. The results will be compared with date of VM attainment, subsequent freezing tolerance and satisfaction of the chilling requirement.

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On average, one year in ten is a true test winter for screening winter hardy plants. Thus, screening of cultural practices under field conditions is often difficult, requiring many years data. In Saskatchewan, the two major winter stresses are low temperature and desiccation. Under controlled lab conditions, a rapid screening method for cultural practices on strawberry (Fragaria × ananassa Duch.) plants was developed. Temperature profiles and survival under various row covers and mulches in this controlled system corresponded well to previous field results. Straw over plastic and snow over plastic row covers conferred the best low temperature protection on these plants.

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In vitro shoot cultures of saskatoon berry were subjected to a 6 week acclimating treatment (4°C/8h day). Acclimated cultures survived freezing to -27°C. Control cultures (24°C/16h day) killed at -6°C. Addition of ABA (5.0 × 10-5M) to growing medium did not increase hardiness of plants under acclimating conditions, but increased hardiness of control plants from -6°C to -10°C.

With standard BA concentration (1.1 × 10-5M) decreased by half, addition of ABA (5.0 × 10-5M) to growing medium resulted in formation of swollen axillary buds with red bud scales. Plantlets on similar medium to which ABA was not added did not show arrested growth or swollen red buds. Following defoliation, removal of shoot apex and transfer to hormone-free medium, buds on ABA-treated plantlets did not resume growth within 30 days. When ABA-treated plantlets were transferred to media supplemented with BA, dormant-looking buds resumed normal growth. Dormant buds collected from field-grown plants and placed in culture broke dormancy on BA medium and maintained the dormant state on hormone-free and ABA medias.

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In North America, over 800 million strawberry crowns are produced by nurseries each year for the strawberry fruit industry. A modeling approach is a quantifiable method to help nurseries predict optimal crown harvest date and potential fruit yield associated with the annual strawberry crown growing environment. Most available models that quantify growth conditions, e.g., chilling effects, use controlled environment chambers and target prediction of time of strawberry flowering, not fruit yield. This study used commercial field fruit yield data over a 6-year period and five geographically distinct locations to construct models to predict the effects of chilling, diurnal temperature difference, and their interaction with daylength on fruit yield and time to flower. Accumulative chilling unit (ACU) was estimated by using nonweighted (simple, M0) and weighted [Mu (Utah Model), M1, M2] accumulation of effective temperature units. The results showed that flowering time correlated with accumulative chilling hours using either a simple (M0) accumulation model or a weighted accumulation model (Mu, M1, M2). The best correlation of flowering time with ACU was a quadratic function (y = 82.27 − 0.049x + 1.74e−5x2, where y = flowering time, x = ACU) and effective temperatures were from –2 to 15 °C. By contrast, fruit yield was only correlated with ACU using specific weighted accumulation models. The correlation was influenced by weighting factors and effective or inhibitive temperatures involved in the model. Therefore, temperatures have differential effects on fruit yield and on flowering time. When pooled across regions and years, fruit yield could be predicted only by the weighted accumulation Model 2 (M2), a quadratic function (y = –72.15 + 0.98x + 0.0022x2) of the ACU accumulated from 45 d before crown harvest. Fruit yield response to ACU had an optimal level with yield reduction at other values. By contrast, fruit yield linearly increased with increasing difference in diurnal temperature across years and locations. However, the days to first flower were affected interactively by the diurnal temperature difference and daylength when geographically distinct locations are compared. The greater the difference in diurnal temperature at 2 to 3 months before crown harvest, the higher the subsequent fruit yield and the shorter the flowering time. An accumulative diurnal temperature unit of 180 degree-days resulted in 30% yield enhancement of Saskatchewan-grown crowns over California-sourced crowns. The greater diurnal temperature difference may be the major contributor to the Northern Vigour® response of strawberry crowns produced in northern latitudes such as Saskatchewan.

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Seed potato growers seek to maximize yields of desirable sized tubers. This study examined how foliar applications of plant growth regulators influence yields of drop or single-cut seed tubers under field conditions. In 1993, paclobutrazol (PTZ; 300, 450, and 600 mg·liter–1), kinetin (KIN; 10 and 20 mg·liter–1), and methyl jasmonate (MJ; 10–7, 10–6, 10–5, and 10–4 M) were applied to `Norland' (NOR) and `Russet Burbank' (RB) potatoes. In 1994, PTZ (300 mg·liter–1), KIN (both rates), and MJ (10–7 and 10–6 M) treatments were eliminated, and GA3 at 250 mg·liter–1 or KIN at 20 mg·liter–1 was applied to some of PTZ treatments. In 1994, the cultivar Shepody (SH) also was included. Plants were treated at two growth stages; NOR (1993), RB (1993 and 1994), and SH (1994) were treated when tubers were <10 mm or <20 mm in diameter. NOR (1994) was treated at stolon initiation (no tubers) or early tuber initiation (<8 mm in diameter). PTZ had no effect on seed tuber (25–50 mm in diameter) yield in NOR in either season. PTZ increased seed tuber number (STN) in RB by 29% to 40% and in SH by 57% to 70% over the controls. KIN had no effect on STN in any cultivar. MJ had no effect on STN in NOR (1993) or in RB in either season or in SH in 1994. In 1994, the highest rate of MJ (10–4 M) increased STN in NOR by 40% over the controls. GA3 had no beneficial effect on STN when applied after PTZ. This study suggests that, under field conditions, PTZ can increase seed tuber production in RB and SH while MJ was effective in NOR potatoes.

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Seeds of celery, spinach, onion, cress, water cress, iceberg lettuce, Great Lakes lettuce, cabbage, tomato, sweet corn and celery were pre-treated with 0.1 μM/g seed of both ABA and analogs of ABA. The chemicals were dissolved in a mixture of methanol:hexane (9:1/v:v) and applied to the seeds for approximately 3 minutes. The solvent was removed from the seeds within 5 minutes by rotary evaporation under reduced pressure. Effects on petri plate germination and soil emergence were monitored daily at 5, 10 and 15°C. The methanol/hexane solvent alone improved spinach seed emergence at 10°C from 10% to 100% and from 50% to 90% at 15°C in celery. Certain ABA analogs reduced time to 50% emergence in celery by at least 7 days at 15°C. Two ABA analogs synchronized emergence in celery and effect was temperature-dependent. One analog improved seed germination in tomato from 15% to 90% at 10°C. In most cases treatment effects on radicle germination on petri plates was not a good indicator of treatment effects on emergence from a soil based system.

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Abstract

Hydrogen cyanamide or hot-water treatment (47C) for 1 hr at the 250°GS (Growth Stage) effectively broke rest in dogwood buds within 10 to 12 days. At this growth stage, control plants grown at 25/18C (day/night) maintained an LT50 of –25C throughout the 3-week study period, whereas plants treated with H2CN2 or hot water gradually lost hardiness. After 3 weeks at 5/2C (day/night), the control plants hardened to a hardiness (LT50) of –45C, and H2CN2-treated plants maintained an LT50 of –25C. The results demonstrate that the extent of acclimation and deacclimaton of dogwood plants may be influenced by environmental temperatures and rest status.

Open Access