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John T. A. Proctor

American ginseng is propagated by seed. In commercial practice ginseng seed is harvested in August or September, placed in a stratification box for about 12 months, and then direct seeded into raised beds. Germination takes place the following spring, some 18 to 22 months after seed harvest. Little is known about the dormancy-controlling mechanisms of ginseng seed. The objective of this study was to investigate seed development and temperature in the stratification box until it was removed 12 months later and seeded in the field. During stratification 3 embryo growth stages were identified. In Stage I of 250 days (September to mid-May) embryo length increased from about 0.5 to 1.0 mm, in Stage II of 100 days (mid-May to late August) length increased to 2.0 mm and in Stage III (late August to late November) length increased to 5.3 mm. Exocarp split width could also be placed in 3 stages. Changes in embryo length correlated with values for embryo: endosperm length ratio. The stratification box temperatures at all depths never exceeded -2°C even when the air temperatures dropped to -13°C and, therefore, were not damaging to the seeds.

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David M. Hunter and John T.A. Proctor

Paclobutrazol applied as a soil drench at 0, 1, 10, 100, or 1000 μg a.i./g soil reduced photosynthetic CO2 uptake rate of leaves formed before paclobutrazol treatment within 3 to 5 days of treatment and the reductions were maintained for 15 days after treatment. The percentage of recently assimilated 14C exported from the source leaf was reduced only at the highest paclobutrazol dose, and there was little effect of treatment on the partitioning of exported 14C between the various sinks. In response to increasing doses of paclobutrazol, particularly at the higher doses, an increasing proportion of recent photoassimilates was maintained in a soluble form in all plant components. Reduced demand for photoassimilates as a result of the inhibition of vegetative growth may have contributed to a reduction in photosynthetic CO2 uptake rate, but this reduction in photosynthesis rate could not be attributed to a feedback inhibition caused by a buildup of starch in the leaves. Paclobutrazol had only a minor effect, if any, on photosynthetic electron transport. Chemical name used: β-[(4-chlorophenyl) methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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David M. Hunter and John T.A. Proctor

A system was developed to evaluate the response of grapes (Vitis spp. `Seyval') to soil-applied paclobutrazol. The youngest fully expanded leaf, and its axillary bud, on single shoots 6 to 9 nodes long developing on rooted softwood cuttings, were retained for use in a bioassay. The shoot that developed from the axillary bud exhibited a dosage-dependent growth inhibition following soil applications of paclobutrazol at 4 dosages between 1 and 1000 μg·g-1 soil. Other aerial components showed no response to paclobutrazol. This test plant system has potential for use in physiological studies with soil-applied plant growth regulators. Chemical name used: β -[(4-chlorophenyl)methyl]- α -(1,1-dimethylethyl)1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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David M. Hunter and John T.A. Proctor

Paclobutrazol applied as a soil drench at 0, 1, 10, 100, or 1000 μg a.i./g soil reduced vegetative growth of `Seyval blanc' grapevines (Vitis spp.). At all rates, there was a reduction in internode length, while at rates higher than 10 μg a.i/g soil, there was also a reduction in node count. Leaf area produced following treatment declined in response to increasing rates, but specific leaf weight increased. Treatment with paclobutrazol delayed senescence and increased the retention of basal leaves that were nearly fully expanded at the time of treatment. Paclobutrazol application had no effect on fruit set or berry size, but the reduction in vegetative growth following treatment decreased the ability of the vine to supply sufficient photoassimilates for fruit maturation. Chemical name used: ß[(4-chlorophenyl)-methyl]-a-(1,1-dimethylethyl)1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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John T.A. Proctor and Ido Schechter

`McIntosh', `Delicious', and `Idared' apple (Malus domestica Borkh.) fruitlet ovaries were artificially damaged with a needle four times after full bloom to assess effects of such damage on fruit growth and development. The damage induced fruit drop, reduced fruit weight, and increased the incidence of fruit deformity, but had no effect on fruit length: diameter ratio. Fruit fresh weight and deformity were correlated with seed per fruit at harvest.

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Jan Schooley and John T.A. Proctor

The Lake Erie counties of southern Ontario, Canada are the major producers of ginseng (Panax quinquefolius) in North America. In this area there is about 1740 ha (4299.5 acres) of ginseng and an annual production of 1455 t (1603.8 tons). Spring freeze damage to the crop is rare as the mean date of last freeze in spring is 12 May. On 21 May 2002, following three to six nights when air temperatures dropped below freezing, extensive damage to the crop was evident. A survey by the Ontario Ginseng Growers Association showed that 78% of growers had gardens showing freeze damage. The extent of the damage was variable across the growing area, and on individual farms. Most damage to plants occurred in low-lying areas where heavy cold air collected. Recently germinated seedlings that were exposed above the straw mulch were severely damaged, and many did not survive because they did not have leaves and no perennating bud was formed. Damage to 2-year-old plants was expressed as leaves wilting and turning black. In some cases stems froze and the plants toppled. In 3-year-old and older plants, damage was variable with some leaf collapse and stems broken, or damaged with corking-over taking place. Damage to inflorescences ranged from death and abscission, to distorted flowers and shriveled and split peduncles. Plant health was a concern following the freeze episode, and throughout the subsequent growing season. The fungicide fenhexamid received emergency registration to combat recurring problems in Botrytis control. The seed crop for 2002 was light. Damaged seedling gardens were replanted. Older gardens will undergo a period of adjustment. Root yield in 2002 was reduced by 30%, a 500 t (551.1 tons) loss. The full extent of the damage and associated financial implications are unknown and could impact the industry until 2005.

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John T.A. Proctor, Dean Louttit, and John M. Follett

Freshly harvested, immature (green) seeds of north american ginseng (Panax quinquefolius L.) were stratified for 12 months either traditionally in buried wooden boxes outdoors, or in plastic pails in a controlled environment room [3 ± 0.2 °C (37.4 ± 0.11 °F)], 85% ± 5% relative humidity) for about 9 months followed by about 3 months at 20 ± 2 °C (69.8 ± 1.1 °F). Embryo growth in Stage II (mid-May to late August when direct seeded) was more rapid [0.016 versus 0.009 mm·d-1 (0.00062 versus 0.00035 inches/day)] under controlled-temperature conditions. Seedling emergence rate did not vary between treatments. Root dry weight (economic yield) was similar for seedling, 2, 3, and 4-year-old plants whether grown from traditionally or controlled-temperature stratified seed. Controlled-temperature stratification of north american ginseng seed is an acceptable alternative to traditional outdoor, in-ground stratification.

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Marilyn H.Y. Hovius, John T.A. Proctor, and Richard Reeleder

American ginseng seed is important as the primary source of propagation. Little is known about ginseng seed stratification and germination. The green seeds are harvested in August/September and stratified in boxes outdoors for 12 to 14 months. Then the after-ripened seeds are field-seeded; they germinate in the spring. Ginseng seeds undergo long dormancy periods caused by embryo dormancy and impermeable seedcoats. The objectives of this research are to shorten the dormancy period, increase the percent germination, and study the changes that occur during stratification using growth regulator and temperature treatments. Seeds stored at 15C from harvest to January and treated with 1000 ppm gibberellic acid (GA3) resulted in the most embryo growth, highest percent germination, and best growth after one growing season compared to 20C and no GA3. Tissue culturing immature zygotic embryos showed a requirement for GA3 (3–5 μM). Radicle growth may need an attached suspensor for development.

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David C. Percival, John T.A. Proctor, and M.J. Tsujita

The influence of irradiance, CO2, and temperature on whole-plant net C exchange rate (NCER) of micropropagated raspberries (Rubus idaeus L. cv. `Heritage') was examined in 1994. Irradiances >1000 μmolm–2–s–1 PAR were required for light saturation, and net photosynthesis (Pn) greatly increased under CO2 enrichment (up to 2000 μlliter–1) and was optimum at 17C. Temperature effects were separated in another experiment using varying air and soil temperatures (15, 20, 25, 30, and 35C) under saturated light and ambient CO2 levels (350 μlliter–1). Both air and soil temperature influenced net Pn, with maximum rates occurring at an air/soil temperature of 17/25C and each contributing 71.2% and 26.7%, respectively, to the total variation explained by a polynomial model (R 2 = 0.96). Dark respiration and root respiration rates also increased significantly with elevated air and soil temperatures. Therefore, results from this study indicate that maximum net Pn occurred at an air/soil temperature of 17/25C and that irradiance, CO2 levels, and shoot and root temperatures are all important factors in examining NCER in raspberries.

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David C. Percival, John T.A. Proctor, and J.P. Privé

Rubus idaeus L. cv. Heritage raspberries were placed in controlled environment chambers (25°C, 14-hour photoperiod, 2.0 kPa vapor pressure deficit, CO2 concentration of 380 mol·m-2·s-1) to study the effects of drought stress on leaf gas exchange and stem water potential. Whole-plant photosynthesis (Pn) and transpiration were sensitive to drought stress and gradually decreased from the second day of the study until rehydration. Stomatal aperture feed-back regulation was present during the initial 48 hours of the study with transpiration rates dropping in response to a decrease in stem water potential. Spatial differences were also present with leaf Pn, and stomatal and CO2 conductance values of the younger, distal (i.e., closer to the apex) leaves decreasing at a faster rate than the older, proximal leaves (i.e., close to crown). Evidence of increased mesophyll resistance to drought stress was apparent with ci either remaining constant or increasing, while Pn and carboxylation efficiency simultaneously decreased. Protection of the underlying photochemistry was evident with parahelionastic leaf movements which resulted in a reduction in the effective leaf area and subsequent heat load. Therefore, an optimum balance between water loss and ci existed, and an alteration in these rates represented a stomatal conductance adjustment to match the intrinsic photosynthetic capacity rather than just a causal relationship.