usually influenced by chilling in winter ( Fuchigami et al., 1982 ; Perry, 1971 ; Wareing, 1956 ). Temperature and duration of chilling are key components of satisfying chilling requirements which are critical to promote vegetative growth and budbreak
Tingting Zhao, Dawei Li, Lulu Li, Fei Han, Xiaoli Liu, Peng Zhang, Meiyan Chen, and Caihong Zhong
Shawn A. Mehlenbacher
Chilling requirements of 44 genotypes of Corylus avellana L. were estimated by cutting shoots in the field at weekly intervals and forcing them in a warm greenhouse for four weeks. The chilling requirements of catkins, female flowers, and leaf buds were assumed to have been met when development occurred on more than half of the respective plant parts. Chilling requirements were lowest for catkins and highest for leaf buds, and ranged from <100 to 860 hours for catkins, 290-1550 hours for female flowers, and 365-1395 hours for leaf buds. The lowest chilling requirements were observed for the leading cultivars of Turkey and southern Italy. The yellow-leafed ornamental C. avellana var. aure a had very high chilling requirements for all plant parts.
Clint Wall, William Dozier, Robert C. Ebel, Bryan Wilkins, Floyd Woods, and Wheeler Foshee III
of growth inhibition of kiwi is apparently in the bud scales because their removal was shown to promote budbreak ( Lionakis and Schwabe, 1984 ). Very little is known concerning the chilling requirement of different kiwi species and cultivars
G. R. McEachern, B. N. Wolstenholme, and J. B. Storey
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.
Chrislyn A. Drake and John R. Clark
Little research has been done to determine the chilling requirement for southern blackberry cultivars. However, field observations from areas where low amounts of chilling occur indicate that `Navaho' requires more hours of chilling than does `Arapaho'. The objective of the study was to determine a method for measuring chilling requirement using whole plants of two blackberry cultivars, Arapaho and Navaho. One-year-old bare-root plants of `Arapaho' and `Navaho' were field-dug and placed in a cold chamber at 3 °C. Ten single-plant replications of each cultivar were removed at 100-hour intervals up to 1000 hours. The plants were then potted and placed in a greenhouse (daily minimum temperature 15 °C) in a completely randomized design. Budbreak was recorded on a weekly basis. Data for budbreak was analyzed as a two-factor factorial (two cultivars and 10 chilling treatments) by SAS and means separated by lsd (P = 0.05). Data indicated that the chilling requirement for `Arapaho' is between 400 and 500 hours. This is evident as a 6-fold increase, which was the largest increase between two chilling treatments, occurred between 400 and 500 hours. For `Navaho', the largest increase (also 6-fold) occurred between 800 and 900 hours, which indicated a chilling requirement for `Navaho' of 800 to 900 hours. These data support previous observations and indicate the method used was successful in determining chilling requirement for blackberries.
Dr. John R. Clark and P. Manjula Carter
The chilling requirements of the University of Arkansas blackberry cultivars Apache, Ouachita, and Prime-Jim*, and the primocane-fruiting selections APF-25, APF-27, APF-40, APF-42, APF-44, APF-46, APF-52, and APF-53 were investigated using stem cuttings from field-grown plants. A biophenometer was used to measure chilling (hours below 7 °C) in the field and 12-node cuttings of lateral shoots were taken from the cultivars every 100 hours up to 1000 hours below 7 °C. However, only 500 chilling hours had occurred at the time of this writing, and the response of budbreak to higher chilling levels could not be reported. The cuttings were placed in a mistchamber in the greenhouse with a daylength of 16 hours and air temperature of 26–29 °C. Percent budbreak was measured weekly. The cultivar × chilling interaction was significant (P = 0.05). `Apache' and `Ouachita' showed little or no budbreak up to 500 h, indicating a higher chilling requirement. The chilling requirement of Prime-Jim was determined to be between 300 h and 400 h, and that of the APF selections appeared to be between 300 h and 500 h. The chilling requirement of APF-53 could not be determined since budbreak was consistent at all levels of chilling up to 500 h. In general, the primocane-fruiting genotypes appeared to require less chilling than floricane-fruiting `Apache' and `Ouachita', and they would therefore be more suitable for low-chill locations.
Iwan F. Labuschagné, J.H. Louw, Karin Schmidt, and Annalene Sadie
Genetic variation in chilling requirement was investigated over three growth periods using clonal progenies of six apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] families derived from crosses of high and low chill requiring cultivars. Two quantitative measurements related to chilling requirement, viz., the time of initial budbreak (vegetative and reproductive) and the number of breaking buds over a specified time interval, were used as evaluation criteria. Genetic and environmental variances of the traits are presented as intra-class correlation coefficients for clones within and between families. For budbreak time, reproductive and vegetative, broad-sense heritability averaged around 75% and 69% respectively, indicating a high degree of genetic determination in this material. For budbreak number, moderate to low genetic determination was found with broad-sense heritabilities around 30%. Estimates of genetic components of variance between families were generally very low in comparison to the variance within families and predict potentially favorable responses to truncation selection on the traits within these progeny groups. Analysis of the data showed that distribution of budbreak time is typical of quantitative traits with means distributed closely around midparent values. Skewed distributions towards low budbreak number were obtained in varying degrees in all families.
Gary A. Couvillon, Nelson Finardi, Marcio Magnani, and Claudio Freire
The rootstock has been shown to influence the chilling requirement of pear (Oregon) (9) and peach (New Jersey) (10). This is not surprising because the rest influence moves across graft unions (1) and the scion and stock differ genetically and may have different chilling requirements. However, it has been reported that under the chilling conditions characteristic of the major California pear districts, rootstock had little or no influence on bloom date or chilling requirement (5). Also, budbreak and/or bloom of ‘Croncels’ (3), ‘Delicious’, and ‘McIntosh’ (4) were not influenced by early and late leafing stocks.
P. Manjula Carter and John R. Clark
Chilling requirement, (the number of hours below 7 °C necessary to break dormancy) has been shown to vary with genotype in blackberry (Rubus subgenus Rubus). Previous work has demonstrated that the chilling requirement of field-grown plants could be accurately determined from stem cuttings of lateral shoots taken at 100-hour intervals of chilling up to 1000 hours, by placing them in a mist chamber maintained at 26 °C with a daylength of 16 hours, and observing budbreak over a period of 5 weeks. This technique has previously demonstrated clear differences in the chilling requirements of thorny and thornless floricane-fruiting cultivars. In the current study, a comparison of floricane-fruiting and primocane-fruiting blackberries using the stem-cutting technique illustrated a lower chilling requirement associated with the primocane-fruiting trait. The use of the stem-cutting technique can be a simple and effective tool for assessing blackberry adaptation to different hardiness zones.
Dale E. Kester
Effect of genotype on variation in chilling requirement among almond seed populations was studied. Pollen of different varieties used on the same seed tree changed embryo genotype and, subsequently, the chilling requirements of the populations of seeds produced. There was a direct correlation between time of bloom of seed and pollen parents and the length of chilling required by their offspring seeds. Chilling requirements were not significantly different in seed populations resulting from reciprocal crosses involving varieties of long and short chilling. Such seed populations had comparable genotypes but were exposed to different maternal effects. Embryo genotype was a controlling factor in determining seed chilling requirement in almond. A distinction between systems affecting inheritance of time of bloom in almond was shown in that ‘Tardy Nonpareil’, a late-blooming bud mutation of ‘Nonpareil’, transmits later bloom to its seedling offspring but did not transmit longer chilling to the seeds.