Nut crop yield records show that budbreak-based chilling requirements may not reflect yield decline chill thresholds

Abstract

TitleNut crop yield records show that budbreak-based chilling requirements may not reflect yield decline chill thresholds Abstract Warming winters due to climate change may critically affect temperate tree species. Insufficiently cold winters are thought to result in fewer viable flower buds and the subsequent development of fewer fruits or nuts, decreasing the yield of an orchard or fecundity of a species. The best existing approximation for a threshold of sufficient cold accumulation, the "chilling requirement" of a species or variety, has been quantified by manipulating or modeling the conditions that result in dormant bud breaking. However, the physiological processes that affect budbreak are not the same as those that determine yield. This study sought to test whether budbreak-based chilling thresholds can reasonably approximate the thresholds that affect yield, particularly regarding the potential impacts of climate change on temperate tree crop yields. County-wide yield records for almond (Prunus dulcis), pistachio (Pistacia vera), and walnut (Juglans regia) in the Central Valley of California were compared with 50 years of weather records. Bayesian nonparametric function estimation was used to model yield potentials at varying amounts of chill accumulation. In almonds, average yields occurred when chill accumulation was close to the budbreak-based chilling requirement. However, in the other two crops, pistachios and walnuts, the best previous estimate of the budbreak-based chilling requirements was 19-32 % higher than the chilling accumulations associated with average or above average yields. This research indicates that physiological processes beyond requirements for budbreak should be considered when estimating chill accumulation thresholds of yield decline and potential impacts of climate change.

Warming Winters Reduce Chill Accumulation for Peach Production in the Southeastern United States

“…Despite research suggesting that declines in crop suitability due to climate change may not be as severe as shown in our results [45], it is worth noting that we examined changes in chill accumulation under a conservative, moderate warming scenario. Provided that some degree of reductions in suitability are anticipated for peach crops across the SEUS-as well as for other crops with similar chill requirements-adaptive measures may be warranted to maintain production.…”

“…While this warming may offer range expansion for cold-intolerant crops, the related reduction in the winter chill accumulation in subtropical climates like the SEUS is projected to have negative impacts on warm-region fruit and nut crops, particularly those with moderate and high chill requirements [20,21]. However, the degree to which these declines may impact crop yield is unclear as uncertainties remain regarding the chill requirements that are physiologically needed for production, and the overall effect of marginal chill accumulation on crop yield and quality [44,45]. For example, while a common commercial peach cultivar grown in central Georgia has a stated chill requirement of 850 h, Georgia peach specialists have suggested that only 800 h are needed for a suitable crop [4].…”

Temperature-related Variables Associated with Yield of ‘Kerman’ Pistachio in the San Joaquin Valley of California

“…To further complicate the logistics of harvesting and marketing the crop, the ability of the pistachio industry to estimate the size of the crop in advance is limited (Klein, 2016). The alternate-bearing nature of pistachio and years with what appears to be insufficient winter chilling complicate estimating annual crop production (Jackson et al, 2009;Pope et al, 2015). Basic physiological information on how annual yield is affected by winter Ta and Ta during the growing season is lacking (Pope et al, 2015).…”

“…The alternate-bearing nature of pistachio and years with what appears to be insufficient winter chilling complicate estimating annual crop production (Jackson et al, 2009;Pope et al, 2015). Basic physiological information on how annual yield is affected by winter Ta and Ta during the growing season is lacking (Pope et al, 2015). Timely advance knowledge of the magnitude of the yield of the next pistachio harvest would be beneficial for the pistachio industry for efficient allocation of harvest and postharvest resources, such as personnel, harvesting machinery, trucks, processing facility capacity, crop storage facilities, and for making marketing decisions.…”

“…Warm Ta occurring during the rest period of temperate fruit and nut trees may delay or prevent the development of adequate rest (Erez et al, 1979;Richardson et al, 1974;Saure, 1985). The dynamic model appears to be gaining support for use in estimating the effectiveness of the rest period (Elloumi et al, 2013;Guo et al, 2013;Pope et al, 2015;Zhang and Taylor, 2011). Zhang and Taylor (2011) determined that a CP accumulation of 59 was sufficient to achieve normal bloom for 'Sirora' pistachio in Australia, whereas Elloumi et al (2013) proposed a CP accumulation of 36 as the threshold for 'Mateur' in Tunisia.…”