Hours Of Chilling Research Articles

Effect of Some Growth Regulators and Nutritional Compounds as Substitutes for Chilling of ‘Delicious’ Apple Leaf and Flower Buds

Abstract Rest of ‘Delicious’ apple (Malus domestica Borkh.) buds was satisfied partially by applications of 6-ben-zylamino purine + gibberellic acid (BA+GA4+7 = Promalin), BA alone, potassium nitrate, and thiourea; GA4+7 alone had no effect. The combination of thiourea and potassium nitrate was as effective as Promalin or BA in stimulating flower bud development. Potassium nitrate had a pronounced effect on forcing flower buds while thiourea had more effect on forcing vegetative buds. BA and Promalin affected both flower and vegetative buds. No treatment affected bloom date or growing degree hours (GDH) required for flower bud expansion under our conditions when applied after 450, 950, or 1200 hours of chilling. Promalin and BA were both effective at 300 and 500 ppm, while thiourea and potassium nitrate were effective at 2% and 3% (w/v), respectively.

Chilling and Budbreak in Lingonberries, Vaccinium vitis-idaea L.1

Abstract Three seedling populations of lingonberries from Fairbanks, Alaska, Oulu, Finland, and the Pasvik River Valley, Norway were exposed to 0, 170, 344, 513, 681, 843, 1013, and 1185 hours of continuous chilling temperatures (4 ± 1°C) to determine chilling requirements necessary to satisfy rest. Both the Finnish and Alaskan populations required at least 681 hours of chilling to obtain maximum terminal vegetative budbreak. Continuous chilling for 1185 hours was insufficient to obtain maximum budbreak in the Norwegian population. In the Finnish and Alaskan populations neither the percentage of stems exhibiting lateral budbreak nor the number of lateral branches per stem differed among chilling treatments. Plants from Norway showed significantly greater lateral budbreak in the 513- and 681-hour treatments than in all other treatments. At least 681 hours of chilling were necessary to achieve normal flowering in the Finnish population.

Mesophilic and Psychrotrophic Bacterial Populations on Hot-Boned and Conventionally Processed Beef'

Mesophilic and psychrotrophic bacterial counts of hot-boned and conventionally treated cuts from 15 steers were low [Log 0–2 colony forming units (CFU)/cm2] at 0 time; and after 14 days of vacuum-packaged storage (2.2 C), hot-boned cuts had higher counts than conventionally-treated cuts. In the first experiment involving 10 steers, the mesophilic and psychrotrophic counts for hot-boned cuts were Log 5.26 CFU/cm2 and Log 5.15 CFU/cm2, respectively, and for conventionally treated cuts, log 4.64 CFU/cm2 and Log 4.43 CFU/cm2, respectively. In the second experiment involving 5 steers, the mesophilic and psychrotrophic counts were Log 6.62 CFU/cm2 and Log 6.61 CFU/cm2, respectively, for hot-boned cuts; and Log 5.93 CFU/cm2 and Log 4.91 CFU/cm2, respectively, for conventionally treated cuts. Some hot-boned cuts had low levels (Log 0–3 CFU/cm2) of coliforms, fecal coliforms, Clostridium perfringens, coagulase-positive Staphylococcus aureus and fecal streptococci. No Salmonella were recovered from any cuts. Temperature-decline data indicated that hot-boned cuts had longer (several hours) periods of rapid bacterial growth (above 21 C) than conventionally-treated cuts. The longer rapid growth period for hot-boned cuts may have contributed to higher microbial loads and subsequently to more growth of bacteria in cold storage. Slower chilling of hot-boned samples stemmed from vacuum-packaging and boxing soon after cutting. Temperature control of hot-boned meat during the first several hours of chilling is critical, particularly if hot cuts are vacuum-packaged and boxed before chilling. Some temperature decline guidelines, based on bacterial counts, are presented for hot-boned, vacuum-packaged boxed cuts. Most hot-boned cuts processed and stored under our experimental conditions were bacteriologically acceptable.

Chilling Requirements of Three Pecan Cultivars1

Abstract Chilling requirements for 3 pecan cultivars are reported for the first time. Stem cuttings with 4 buds of ‘Desirable’, ‘Mahan’, and ‘Stuart’ pecan (Carya illinoensis (Wang.) K. Koch) were forced in a greenhouse after each 100 hours of field chilling below 7.2°C during the 1969-70, 1970-71 and 1971-72 dormant seasons and bud break measured 21 days later. A chilling requirement of 500 hours was determined for ‘Desirable’ and ‘Mahan’, and 600 hours for Stuart.

Effects of Cold Storage Duration on Bud Dormancy and Root Regeneration of White Ash (Fraxinus americana L.) Seedlings1

Abstract Root regeneration and time to first budbreak of two-year white ash (Fraxinus americana L.) seedlings were strongly correlated with the number of hours of chilling. Physiological dormancy of the buds was removed after approx 2500 hours of storage at 5°C and this coincided with the beginning of increased root regeneration potential. Increased periods of chilling enhanced the rate at which growth was resumed after transfer of seedlings to environmental conditions adequate for growth. The present study indicates that fall-harvested white ash seedlings can be stored at 5° at least until May without any apparent detrimental effects on root regeneration potential or seedling condition.

Effects of autumn on the induction of dormancy in apple and peach seedlings and their subsequent regrowth in spring

Apple and peach seedlings were grown for 8 weeks under various regimes: two photoperiods (16 and 8 hr), two air temperatures (12.8° and 18.3°C) and three root temperatures (12.8°, 18.3° and 23.9°C). After the leaves were removed the seedlings were chilled in the dark at 5.6° for three periods (apples 750, 1500 and 2500 hr; peaches 750, 1500 and 2000 hr) and then grown in a glasshouse for 7 weeks during which bud break and extension growth were measured. Growth of apple seedlings (cv. Granny Smith) stopped in an air temperature of 12.8� irrespective of photoperiod and root temperature. At 18.3° growth continued, but was retarded by short days and a root temperature of 12.8°. Peach seedlings (cv. Elberta) did not grow after any of the treatments. Extension growth and bud break in both species increased with increased hours of chilling. Pre-dormancy factors had no effect on bud break in apples, but low air temperature and short days prior to chilling increased bud break in peaches, although the effects decreased as chilling increased. Low pre-dormancy air temperature increased the growth of both species after chilling. Photoperiod produced opposite effects in the two species. Thus short days increased the growth of peaches while long days were effective with apples. Apples grew best at a root temperature of 12.8°, and peaches grew better at this temperature than at 18.3° but not as well as at 23.9°.

Chilling requirements of the apple cultivar Stoke Red

Trees of the apple cultivar Stoke Red were chilled at temperatures between 2�C and 10�C for periods up to 3000 hours. Extension growth and budbreak increased with increasing hours of chilling and decreasing temperatures. The cultivar was shown to require more chilling than is provided by southern Victorian winters.

Reversibility of Chilling Injury to Corn Seedlings

Seedlings of corn (Zea mays) were tested for recovery from chilling injury incurred at 0.3 +/- 0.3 C. At 0.3 C visual leaf injury appeared in 36 hours, whereas stem and root injuries appeared later. Appearance of leaf injury was preceded by a rise in O(2) uptake and a lessened effect of 2,4-dinitrophenol on O(2) uptake by leaf segments and was accompanied by increased ion leakage from the leaves. These effects were reversible, in that transfer of seedlings to 21 C after 36 hours at 0.3 C produced a return of O(2) uptake, 2,4-dinitrophenol stimulation, and ion leakage to the levels of unchilled leaves, as well as a disappearance of leaf symptoms, within 72 hours. For most seedlings, transfer to 21 C after 48 to 60 hours at 0.3 C reversed the chilling effects on O(2) uptake, 2,4-dinitrophenol stimulation, and injury symptoms but not on ion leakage within 108 hours. However, some seedlings collapsed during 48 to 60 hours of chilling, and these never recovered. Transfer to 21 C after 72 hours at 0.3 C did not produce recovery from any symptom of chilling injury examined, and these seedlings soon died. No growth occurred at 0.3 C, but growth began soon after transfer to 21 C. Seedlings chilled 24 or 36 hours grew at reduced rates during the first 72 hours at 21 C, but within 96 hours at 21 C were growing at the same rate as nonchilled seedlings. These results demonstrate considerable capacity of growing plants to recover from short chilling treatments even though significant physiological changes occurred at low temperatures.

Sweetgum Dormancy Release: Effects of Chilling, Photoperiod, and Genotype

AbstractIn Liquidambar styraciflua L., 1200 to 1600 hours of chilling (3°C) resulted in rapid resumption of growth under greenhouse forcing conditions. Long photoperiods were effective substitutes for chilling. Plants from southern Alabama (Lat. 31°) had a lower chilling requirement than those from western Tennessee (Lat. 36°). Growth rate of plants under long photoperiod varied directly with degree of previous chilling.