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Timothy A. Prince and Maria S. Cunningham

Exposure of bulbs of Easter Lily (Lilium longiflorum Thunb.) to a maximum of 2 μl ethylene/liter during vernalization delayed flowering by 5 to 7 days and decreased the number of flower buds. Ethylene exposure for 5 days at 21C after vernalization accelerated shoot emergence and flowering by up to 3 days. No floral or plant abnormalities were observed after bulb exposure to ethylene. Exposure to atmospheres with 0%, 0.5%, or 1% O2 at 21C for up to 2 weeks before or 10 days after vernalization did not “significantly impair subsequent bulb forcing. Storage in 1% 02 at 21C for 1 week before vernalization resulted in nearly one additional secondary bud initiated per plant. Exposure to up to 15% CO2 at 21C for up to 2 weeks before or 10 days after vernalization did not significantly impair subsequent forcing.

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Dario J. Chavez, Thomas G. Beckman and José X. Chaparro

. Nuclear genes. Single-copy genes associated with vernalization response (33), two major genes associated with tree architecture, and three genes expressing isozymes were included in this study. Hereafter, gene symbols will be used for these regions

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Jules Janick

Concerning the essence of the winter habit brought Lysenko into prominence. Although what was to be dubbed vernalization had been long a subject of physiological study in the 19th century, Lysenko initiated the practical benefits of this practice by using

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Schuyler D. Seeley

Forcing plant material has long been used to determine dormancy intensity (DI) in woody species. Forcing with growth regulators may enhance this ability. Some forcing with naturally occurring hormones may be showing us the actual DI of certain materials. But, measurements of DI that use caustic, near-lethal treatments, or metabolic agents may be all or nothing breaking indicators acting on mechanisms other than the dormancy mechanism and thus not as useful in determining DI. It is possible to cause a meristem to break without completely breaking dormancy. Measurement of normal post-dormancy growth is necessary to determine the effect of a DI agent. DI breaking treatments that act on the dormancy mechanism can cause a temporary growth flush, but, unless the extent of that growth flush is measured and compared with the growth flush of the same normally broken plant material, its true effect remains unknown. In some plant material, the safest way to determine DI is to determine the chilling required to produce normal growth. This assumes that the vernalization requirement and temperature response curves are known for the plant in question. In peach, for instance, vernalization at 2C will cause seeds to germinate, but the resulting seedlings will be physiologically dwarfed. Vernalization at 6C or at 2C cycled with higher temperatures within the vernalization range results in normal seedlings. This indicates that, for chilling to progress normally, vernalization per se must be interspersed or concomitant with growth heat units. Vernalization, therefore, has a low temperature driven component and a heat requiring development and/or growth component. Vernalization driving conditions are slowly being elucidated. Each clarification requires modification of dormancy models. DI does not equal dormancy status!

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Hrvoje Rukavina* and Harrison Hughes

Efforts are ongoing at Colorado State Univ. to develop cultivars of saltgrass for turf use. Crossing among genotypes have been limited because of the species' short flowering period that generally occurs in late May or early June. Therefore, this study was made to establish a floral induction procedure for saltgrass to facilitate winter crosses in the greenhouse. The effects of vernalization/photoperiod, nitrogen and burning on the flowering induction of three saltgrass genotypes were investigated in the Colorado State Univ. greenhouse. Genotypes 49 and C66 from South Dakota and Nevada, respectively did not respond to flowering induction treatments. Only genotype A54 from the Colorado Front Range gave adequate response to flowering induction treatments. Saltgrass genotype (origin of clone) is a major factor relative to floral induction with the treatments used. All three treatment factors significantly influenced the number of spikes or flowering in saltgrass clone A54. There was a highly significant effect of vernalization/photoperiod (P < 0.01) and burning treatment (P < 0.01), with a smaller but significant interaction (P <0.05) among these two factors. There was also a significant effect of nitrogen (P <0.05). Burning had a significant influence on flowering only in treatments without vernalization/photoperiod effect. Vernalization/photoperiod levels significantly influenced flowering regardless of the burning treatment. Since flowering induction requirements differ among saltgrass genotypes originating in different areas, further studies will evaluate more Colorado genotypes as well as different lengths of vernalization/photoperiod on efficiency of flower induction.

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Mary Ruth McDonald*, Kevin Vander Kooi, Cathy Bakker and Alan McKeown

Globe artichoke (Cynara scolymus L.) is a high value cool season crop which requires vernalization to induce flower formation. The climate in Ontario does not allow for survival of perennial cultivars or for consistent natural vernalization of annuals. Three methods of vernalization were tested: a controlled environment chamber, a lighted cold storage, or GA3 application in the field. Plants, cv. Green Globe Improved, were grown in a greenhouse set at 25 °C day temperature in 72-cell Styro-foam trays in a peat mix. At 4 weeks, plants receiving vernalization were transferred to growth chambers, or lighted coolers (four standard 8 foot cool white fluorescent lamps) at 10 °C for two weeks. The others stayed in the greenhouse. GA3 treatments (PROGIB, 15 g ai/ha) were applied at 2, 4 and 6 weeks after transplanting. Cultivars Green Globe Improved, Imperial Star, Emerald, and Large Green Globe were evaluated in separate trials. Trials were conducted at Simcoe, on coarse sand in a high heat area, and Kettleby, on organic soils in a cooler area of Ontario. Shortly after planting at Simcoe several 30 °C days occurred which devernalized and injured the crop. Artichokes grew well at the Kettleby site. Vernalization in the growth chamber was most effective and resulted in the earliest bud formation and highest total yield (1503 cases/ha). Large Green Globe was not well adapted to Ontario conditions. Imperial Star and Emerald produced the highest yields, 2180 and 1779 cases/ha, respectively. Globe artichokes can be grown successfully as an annual crop in cool production areas of Ontario.

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Wayne Brown, Theo J. Blom, George C.L. Chu, Wei Tang Liu and Lisa Skog

The sensitivity of easter lilies (Lilium longiflorum) to either ethylene or methane (products of incomplete burning in gas-fired unit heaters) was tested during rooting [3 weeks at 18 °C (65 °F)], vernalization [6 weeks at 6 °C (43 °F)] and subsequent greenhouse forcing (15 weeks at 18 °C). Starting at planting, easter lilies were exposed for one of seven consecutive 3-week periods (short-term), or for 0, 3, 6, 9, 12, 15, 18, or 21 weeks starting at planting (long-term) to either ethylene or methane at an average concentration of 2.4 and 2.5 μL·L-1(ppm), respectively. Short- or long-term exposure to ethylene during rooting and vernalization had no effect on the number of buds, leaves, or plant height but increased the number of days to flower. Short-term exposure within 6 weeks after vernalization reduced the number of buds by 1 bud/plant compared to the control (no ethylene exposure). However, extensive bud abortion occurred when plants were exposed to ethylene during the flower development phase. Long-term exposure to ethylene from planting until after the flower initiation period resulted in only two to three buds being initiated, while continued long-term exposure until flowering caused all flower buds to abort. Short-term exposure to methane at any time had no effect on leaf yellowing, bud number, bud abortion, or height and had only a marginal effect on production time. Long-term exposure to methane from planting until the end of vernalization increased both the number of buds, leaves and height without affecting forcing time, leaf yellowing or bud abortion.

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R.M. Warner, J.E. Erwin and A.G. Smith

Previous research indicated that Raphanus sativus L. `Chinese Radish Jumbo Scarlet' (CJRS) has an obligate vernalization requirement for flowering and can be vernalized as an imbibed seed in less than 10 days at 6 °C. For these reasons, it serves as an excellent model system for vernalization studies. This study was initiated to gain an understanding of the interaction between cold duration, exogenously applied GA3, and photoperiod on R. sativus CJRS flowering. R. sativus CJRS seeds were sown in 90-mm petri plates on Whatman no. 1 filter paper saturated with plain water or a solution containing 10-5 M or 10-3 M GA3. After germination (i.e., when the radicle was visible), seedlings were either directly transplanted into 10-cm pots and placed in a greenhouse, or transferred to another petri plate onto filter paper saturated with water only and placed in a growth chamber at 6 °C (75 μmol•m-2•s-1 for 8 h) for 2, 4, 6, 8, or 10 days. Greenhouse conditions were: 20 °C, ambient light (December to January, St. Paul, Minn.) plus 70 μmol•m-2•s-1 supplemental light (high-pressure sodium lamps, 0830-1630 hr), under either an 8-h photoperiod (covered with opaque cloth from 1630-0830 hr), or ambient photoperiod plus night-interruption lighting (2 μmol•m-2•s-1, using incandescent lamps, 2200-0200 HR). Results will be presented.

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John M. Rariden and Douglas V. Shaw

Runner plants from 16 strawberry (Fragaria ×ananassa Duch.) cultivars were grown using annual Mediterranean production systems to test for differences in productivity, performance traits, and vegetative growth attributes. Genotypes were included from germplasm adapted to four geographic regions: California and northwestern, northeastern, and mid-Atlantic or southeastern United States. The California genotypes were divided further into day-neutral and June-bearing categories. With these treatments, California cultivars had significantly larger plants and grew more rapidly during the fall and winter, had larger fruit, and produced at least twice the quantity of fruit of cultivars from the other regions. Variance components due to region explained 64% and 26% of the phenotypic variance for early and total yield, respectively, whereas differences among cultivars within regions explained 12% and 7% of the variance for these traits. Cultivars from all regions had significantly larger plants and were more productive when treated with 3 weeks of artificial vernalization. However, region × vernalization effects were nonsignificant for all traits, a result suggesting that selection in Mediterranean environments has not adapted germplasm specifically for low vernalization conditions.

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Smiljana Goreta, Lovre Bucan, Gvozden Dumicic and Daniel I. Leskovar

Globe artichoke is a native crop of the Mediterranean region with about 80% worldwide production. It is estimated that about 3,000 ha are grown in the U.S., mostly in California. Artichoke crop can be grown as a perennial, by vegetative cuttings, or as annual by seeds. Crop production can be limited by freezing winter temperatures leading to irreversible plant damage or by high summer temperatures causing poor head quality. Successful artichokes production, particularly in areas with constraining climatic conditions, requires proper selection of cultivars and planting dates. Cultivars with low vernalization requirements are more prone to a short growing season. The application of GA3 to overcome the lack of low temperatures and fulfill the vernalization requirements of early cultivars is well known. The goal of this multi-year project is to select production strategies contributing to earliness, extension of harvesting period, and improved yield and head quality under a variety of environmental conditions in Croatia and Texas. Selecting cultivars with different maturity groups and planting dates enabled harvesting period from autumn to late spring depending on locations. When GA3 was applied (12.5 to 125 ppm) on a naturally vernalized crop from autumn planting, early yield was substantially increased without affecting earliness. Conversely, application of GA3 (30 or 45 ppm) on nonvernalized plants established during late spring or summer was necessary for fall harvest in the Croatian locations. Head quality evaluated as head weight and size, or crude protein and total fiber concentration, progressively decreased during late spring harvest in Texas. Shifting the harvesting period towards early spring may be essential for improving head quality and for increasing the market share. To achieve adequate yields, longer harvesting period, and superior head quality, it is necessary to develop and adjust cultural practices for the specific growing area.