Search

Pulsatilla cernua var. koreana seeds were harvested at six different dates between 16 days after flowering (DAF) (8 Apr.) and 43 DAF (5 May) in 2018 and categorized into six groups based on X-ray images. Germination tests were performed without and with 2 weeks of moist 5 °C treatment [cold stratification (CS)]. Seeds harvested at 38 DAF (30 Apr.) with well-developed vegetative organs (embryo and endosperm) in seeds categorized as A and B (seed A and seed B, respectively) based on the X-ray images were considered fully developed, and 80% of seeds were considered mature. However, the germination rates were less than 26% or 28% when full seeds harvested at 43 DAF received no or 14 days of CS treatment, respectively. Our study suggests that the low germination rate of fully developed seeds as judged by X-ray images showing well-developed embryo and endosperm could result from the presence of dormancy that was not broken effectively by 14 days of CS coupled with the loss of viability caused by 8 months of dry storage at 5 °C.

Flowering of the herbaceous perennial Aquilegia is generally considered to require vernalization after seedlings are mature, whereas photoperiod has little or no effect. We performed experiments to determine the flowering responses for two Aquilegia ×hybrida varieties, one of which reportedly has reduced cold requirements. Seedlings of Aquilegia ‘Origami Blue and White’ and ‘Winky Double Red and White’ with three to five leaves were either placed directly into a 5 °C cooler with low-intensity lighting for 9 hours/day or transplanted to 13-cm containers and grown (bulked) for 0, 3, or 6 weeks at 20 °C under 9-hour short days (SDs) or 16-h long days (LDs). Plants were then cooled at 5 °C for 0, 5, or 10 weeks and placed in a common forcing environment at 20 °C under LDs. Flowering response of the two cultivars differed markedly. All Aquilegia ‘Origami Blue and White’ plants placed directly into the forcing environment flowered and in a mean of 93 days. Flowering percentage of plants cooled in the plug tray decreased with increasing duration of cold treatment, and only 15% flowered after a 10-week cold treatment. All plants bulked for 3 or 6 weeks before cold treatment flowered after 25 to 36 days in the forcing environment. Adding bulking and forcing time together, time to flowering of ‘Origami Blue and White’ was complete and most rapid (62 days) when plants were bulked for 3 weeks under SDs and then forced under LDs. In contrast, no ‘Winky Double Red and White’ plants flowered without cold treatment, and 6 weeks of bulking followed by 10 weeks of cold was required for 100% flowering. These results indicate that ‘Origami Blue and White’ has a relatively short juvenile phase and flowering was promoted by SD bulking or cold treatment, whereas ‘Winky Double Red and White’ has a longer juvenile phase and requires cold for flowering.

Seeds of temperate fruit species need a long time to germinate as a result of their requirement of stratification or cold treatment. Therefore, fast and uniform germination techniques are desirable and important for fruit tree propagation and especially for breeding studies. The effects of combinations of benzylaminopurine (BAP) and gibberellic acid (GA3) on in vitro embryo germination of apricot, peach, and wild cherry were determined without seed cold pretreatment. The results showed that no germination was recorded in all the seeds with testa. In the seeds without testa, no germination (wild cherry) or limited germination (less than 10%) was recorded. When the embryos separated from cotyledons were cultured, successful germination was obtained for all species. In general, the addition of different combinations of BAP and GA3 into the Murashige and Skoog (MS) medium significantly increased the germination ratios of embryos without cotyledons in all species. For wild cherry, the best treatment (66.7% germination) was MS media containing 0.5 mg·L−1 BAP + 2.0 mg·L−1 GA3 or 0.5 mg·L−1 BAP + 4.0 mg·L−1 GA3. For peach, the best treatment (86.7% germination) was MS medium supplemented with 0.5 mg·L−1 BAP + 3.0 mg·L−1 GA3. For apricot, the best treatment (93.3%) was MS media containing 0.5 mg·L−1 BAP + 3.0 mg·L−1 GA3, 1.0 mg·L−1 BAP + 1.0 mg·L−1 GA3, or 1.0 mg·L−1 BAP + 2.0 mg·L−1 GA3.

`Snowcap' Shasta daisy [Leucanthemum ×superbum Bergmans ex. J. Ingram (syn: Chrysanthemum ×superbum, C. maximum)] was grown under various photoperiods and temperatures to determine their effects on flowering. In the first experiment, plants were held for 0 or 15 weeks at 5 °C and then were grown at 20 °C under the following photoperiods: 10, 12, 13, 14, 16, or 24 hours of continuous light or 9 hours with a 4-hour night interruption (NI) in the middle of the dark period. Without cold treatment, no plants flowered under photoperiods ≤14 hours and 65% to 95% flowered under longer photoperiods or NI. After 15 weeks at 5 °C, all plants flowered under all photoperiods and developed three to four or 10 to 11 inflorescences under photoperiods ≤14 or ≥16 hours, respectively. To determine the duration of cold treatment required for flowering under short photoperiods, a second experiment was conducted in which plants were treated for 0, 3, 6, 9, 12, or 15 weeks at 5 °C, and then grown at 20 °C under 9-hour days without or with a 4-hour NI. Under 9-hour photoperiods, 0%, 80%, or 100% of plants flowered after 0, 3, or ≥6 weeks at 5 °C, and time to flower decreased from 103 to 57 days as the time at 5 °C increased from 3 to 12 weeks. Plants that were under NI and received ≥3 weeks of cold flowered in 45 to 55 days. For complete and rapid flowering with a high flower count, we recommend cold-treating `Snowcap' for at least 6 weeks, then providing photoperiods ≥16 hours or a 4-hour NI during forcing.

Release, localization, and concentration of essential oils in chilling-injured and noninjured lemon [Citrus limon (L.) Burm.] fruit were investigated to enhance understanding of how chilling injury (CI) occurs in lemon. CI in the form of moderate to severe pitting of the flavedo was initially apparent after 3 weeks at 1 °C, followed by a gradual increase in severity until termination of the experiment after 7 weeks at 1 °C. Curing the fruit at 15 °C for 1 week before cold treatment greatly reduced the severity of CI. Release from the fruit of d-limonene, a major component of essential oil in lemon, increased with increasing amounts of CI. The enhancement of d-limonene release, however, lagged behind the development of CI. Studies of the internal anatomy of the flavedo using confocal microscopy indicated that essential oils were abundantly present inside the oil gland and in oil bodies outside the gland. Chilling-injured flavedo exhibited no obvious disruption of either the oil glands or the oil bodies. Extraction and quantification of d-limonene from chilling-injured and noninjured flavedo indicated that similar amounts of oil were present in the tissue, regardless of injury. Damage to the flavedo after 3 weeks at 1 °C was noted in the form of flattened or collapsed cells between the top of the gland and the epidermis, whereas collapse of the oil gland only was observed in later stages of injury development.

In accordance with the currently approved Australian citrus disinfestation protocol for export to Japan, degreened `Eureka' lemons [Citrus limon (L.) Burm.] were cold-stored for 2 weeks at 1C. Following cold treatment, fruit were stored at 5C for 3 weeks, then transferred to 20C for an additional week to simulate transportation and handling. Fruit harvested early in the season were more susceptible to chilling injury than fruit harvested later, with 62% having lesions >1 cm2 after 2 weeks at 1C. Most of the chilling injury occurred after subsequent storage (at 5C) rather than immediately after the 1C treatment. Injury was different from surface pitting or oleocellosis, manifesting as large uniform surface lesions 2 to 3 cm in diameter that rapidly discolored following storage at 20C. Although the oil glands were flattened, the collenchyma layer immediately above the oil gland remained intact. Cellular discoloration was localized around the oil gland, possibly indicating a lateral release of oil gland contents. Nondegreened late-season fruit developed substantially lower levels of chilling injury.

Phlox paniculata Lyon ex Pursh `Eva Cullum' plants were grown under seven photoperiods following 0 or 15 weeks of 5 °C to determine the effects of photoperiod and cold treatment on flowering. Photoperiods were a 9-hour day extended with incandescent lamps to 10, 12, 13, 14, 16, or 24 hours; an additional treatment was a 9-hour day with a 4-hour night interruption (NI). Noncooled plants remained vegetative under photoperiods ≤13 hours; as the photoperiod increased from 14 to 24 hours, flowering percentage increased from 20 to 89. Flowering of noncooled plants took 73 to 93 days. Flowering percentage was 19, 50, or 100 when cooled plants were held under photoperiods of 10, 12, or ≥13 hours or NI, respectively. Time to flower in cooled plants progressively decreased from 114 to 64 days as the photoperiod increased from 10 to 24 hours. Reproductive cooled plants had at least three times more flowers, were at least 50% taller, were more vigorous, and developed seven or eight more nodes than did noncooled plants. Photoperiod had no effect on height of flowering plants.

A reduced heat shock period for `Sharwil' avocado (Persea americana Mill.) before quarantine cold treatment is described. The shortened heat pretreatment period of 8 to 12 hours, rather than the originally recommended 18 hours at 38C, is effective in reducing chilling injury symptoms when the pulp is at ≤2.2C during 16 days of storage. The reduced durations and the range of pretreatment hours affords packinghouses greater efficiency and more flexibility and will reduce handling costs relative to the longer exposure.

The energy and carbon needs for early shoot growth in tulips are mainly provided by reserve carbohydrates in bulbs. The cold-treatment of bulbs before greenhouse forcing enhances the breakdown and remobilization of reserve carbohydrates in bulb scales, and is necessary for proper shoot growth and flowering in tulips. Tulip bulbs are known to contain both starch and fructans as reserve carbohydrates. We evaluated several extraction solvents, including ethanol and distilled water, and several extraction temperatures to accurately determine the amounts of different types of non-structural carbohydrates in tulip bulb scales. Extraction with distilled water resulted in excessive solubilization of starch. For example, extraction at 70 °C solubilized more than 80% of starch to glucan polymers. On the other hand, 80% ethanol at 70 °C extracted all soluble sugars including fructans with no apparent solubilization of starch. The changes in non-structural carbohydrates in the outermost bulb scale of tulip (Tulipa gesneriana L. `Frankfurt') during 12 weeks of cooling at 8.8 °C followed by 5 weeks of greenhouse forcing were determined. Starch was the major carbohydrate in bulb scales consisting of ≈70% of the dry weight at the beginning of cold treatment. Starch content per scale decreased slightly during cold treatment, but rapidly after transferring to greenhouse. Sucrose and soluble fructan content per scale increased during cold treatment, then decreased after transferring to greenhouse. Glucose content per scale remained fairly constant during cooling and greenhouse forcing, while fructose content increased in the greenhouse.

Six tomato cultivars [Hotset, Petra, Stella, Big-O, Tropic, & Monte Carlo (fresh market)] were grown in a greenhouse in 1979 from July through November in 3 experiments. Exp. 1: The first two cultivars were used in a 15 cm, 30 cm, or 45 cm in-row spacing with rows spaced 60 cm apart. Cumulative fruit number and weight per unit area declined with increasing in-row spacing. Exp. 2: The first four cultivars were subjected to either cold or no cold treatment during germination before transplanting. No differences were found between the two treatments for mean fruit weight or total fruit number. Exp. 3: The last two cultivars were subjected to both the cold treatment and flower vibration. Cumulative fruit weight was greater for vibrated flowers. Greater mean fruit weight occurred earlier with cold treatment and declined significantly later in season, and was more pronounced in Tropic than Monte Carlo.

An approved quarantine treatment for Tephritid fruit fly control of citrus fruit requires fruit be held at 0.0-2.2C for 10-22 days, depending on fruit fly species involved and actual temperature attained. However, this treatment causes chilling injury (CI) in California-Arizona desert lemons harvested in late summer or early autumn. We found that temperatures at which lemons are held before cold treatment affects the susceptibility of lemon fruit to CI. Commercially packed lemons obtained from Yuma, AZ packinghouses in Sept.-Nov. 1987 and 1988 were held at 1C for 3 or 6 weeks, or cured for one week at 5, 15 or 30C, or at 15C for one week, followed by 30C for one week, before receiving the 1C cold treatment. Lemons cured one week at 5 or 15C before the cold treatment developed at least 25-30% less CI during 4 weeks peat treatment storage at 10C than noncured fruit. The other curing treatments were not as effective for reducing CI.

Established shoot cultures of three apple genotypes, `Dayton', `McIntosh', and `Golden Delicious' were subcultured into culture tubes containing a modified MS medium and maintained in a dark chamber at 1.0±0.5°C for periods of 3, 6, 9, and 12 months. Following each cold storage period, culture tubes of each of the three genotypes were transferred to a growth room and maintained under 16 h of light (60 uEs-1m-2) and 21°C. The overall morphological condition of each shoot was then recorded. After 4 weeks of growth, both number and length (in cm) of proliferating shoots were recorded. In general, shoots subjected to 3 or 6 months of cold storage remained green however most cultures did not initiate any new shoots. Cultures subjected to 9 or 12 months of cold treatment were etiolated however new axillary shoots were observed. The proliferation rate after 4 weeks of growth under standard growth conditions were variable among the different genotypes. The implications of using long term cold storage of apple shoot cultures will be discussed.