A Review of Winter Chilling Requirements in Pecan. Eric T. Stafne Associate Extension and Research Professor Mississippi State University

Transcription

1 A Review of Winter Chilling Requirements in Pecan Eric T. Stafne Associate Extension and Research Professor Mississippi State University

2 What is Chilling? A physiologically mandated rest period Also called Dormancy Helps to regulate timing of budbreak Begins in late summer when shoot growth stops

3 Chilling Accumulation Occurs when temperatures are below 45 F but above 32 F If below 32 F, then no accumulation (too cold) If above 45 F, then no accumulation (too warm) If temperatures get too hot (above ~70 F) then chilling can be lost

4 Rest Control Rest is controlled by several factors: Exposure of buds to cold temperatures Homones such as abscissic acid Light intensity Day length

5 Quiescence A state that is temporary and of usually short duration The in-between period when chilling has been satisfied but heat accumulation not met No budbreak occurs

6 Heat Accumulation When temperatures are sufficiently warm enough to satisfy end the quiescent phase of dormancy If not enough chilling then more heat needed for budbreak

7 Budbreak Closely associated with chilling requirement Long chilling requirement = later initiation of growth Short chilling requirement = earlier initiation of growth

8 Budbreak Regulation An evolutionary survival mechanism Allows for adaptation of the species throughout a large range Varies throughout the native range

9 Deficiency of Chilling In southern areas Results in: Prolonged dormancy Delayed leafing out Increase in fruit drop Reduced yields

10 New Climate Concerns Early Spring re-initiation of growth Cold weather and damaging frosts still possible, more likely farther north Mississippi has a continental climate with wildly fluctuating winter temperatures (esp. N. MS)

11 The Role of Chilling Hours First described for pecans in 1925 by Waite A few studies done to determine chilling requirements for different pecan cultivars

12 McEachern et al Used non-terminal stem cuttings Desirable and Mahan required 500 hours of chilling Stuart required 600 hours

13 Amling and Amling 1980 Used detached cuttings Mahan, Success, Desirable, and Schley required hours Stuart required hours Rest intensity enhanced if trees have green leaves or fruit when exposed to chilling temperatures

14 Smith et al Used seedlings Found that terminal buds had lower chilling requirement than lateral buds (Kuden et al found differences between male and female flowers too) Days to budbreak declined as chilling hours increased

15 More Smith Uniformity of budbreak associated with increase in chilling hours Dodd seedling required 900 hours

16 Sparks 1993 Used own rooted Stuart Found that Stuart could break bud without any chilling

17 More Sparks Chilling decreased the number of days to budbreak 0 chilling hours = 44 days to budbreak 800 chilling hours = 22 days to budbreak

18 The Role of Heat Accumulation Heat is required for budbreak Budbreak occurs under an interaction of chilling and heating

19 Heat Accumulation Date of budbreak varies depending on the rate of heat accumulation following completion of chilling If sufficient heat is accumulated without chilling budbreak can still occur

20 Sparks 1993 Budbreak determined by interaction of low followed by high temperatures Heat requirement decreased with increased chill accumulation Budbreak could occur without chilling as long as heat accumulation met However, variability in budbreak occurred

21 Heat Requirements Sparks (1993) found that temperatures less than 36 F did not promote budbreak The most efficient temperature to base chill and heat accumulation was 39 F

22 Conclusions Budbreak is under an interaction between chilling and heat accumulation Variability among different pecan genotypes is under genetic, and not environmental, control Most pecans grown here fall between hours

23 More Conclusions Pecan genotypes are genetically programmed to have certain chilling requirements Mississippi has a wide range of chilling But, most years the chilling requirement is met

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27 Specific Location in Mississippi

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29 Just a Little Patience The calculations can take some time Complex calculations from another database (Weather underground) Let us know if you see areas that need improvement

30 Comments Most accurate measurement of chill hours is from a device within your field. Data in this application is based on actual measurements, but use as a general guideline and not as an exact value because weather varies from location to location. This app has been created to help Mississippi fruit/nut growers assess growing conditions that impact plant physiology and to help them prepare for events in the upcoming season. If you have questions or comments, please contact Eric Stafne at eric.stafne@msstate.edu

31 Computer or Mobile device 1. Type in this URL on mobile device (e.g. smartphone, tablet) also works on Desktop computers 2. It asks you to save it to your home screen 3. It creates icon like any other app 4. Done and enjoy!