Dormancy in temperate fruit trees in a global warming context: A review

Responses of spring phenology in temperate zone trees to climate warming: A case study of apricot flowering in China

Flowering plants initially diversified during the Mesozoic era at least 140 million years ago in regions of the world where temperate seasonal environments were not encountered. Since then several cooling events resulted in the contraction of warm and wet environments and the establishment of novel temperate zones in both hemispheres. In response, less than half of modern angiosperm families have members that evolved specific adaptations to cold seasonal climates, including cold acclimation, freezing tolerance, endodormancy, and vernalization responsiveness. Despite compelling evidence for multiple independent origins, the level of genetic constraint on the evolution of adaptations to seasonal cold is not well understood. However, the recent increase in molecular genetic studies examining the response of model and crop species to seasonal cold offers new insight into the evolutionary lability of these traits. This insight has major implications for our understanding of complex trait evolution, and the potential role of local adaptation in response to past and future climate change. In this review, we discuss the biochemical, morphological, and developmental basis of adaptations to seasonal cold, and synthesize recent literature on the genetic basis of these traits in a phylogenomic context. We find evidence for multiple genetic links between distinct physiological responses to cold, possibly reinforcing the coordinated expression of these traits. Furthermore, repeated recruitment of the same or similar ancestral pathways suggests that land plants might be somewhat pre-adapted to dealing with temperature stress, perhaps making inducible cold traits relatively easy to evolve.

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Adaptation to seasonality and the winter freeze

Apple pollination: A review

In the current context of global warming, an analysis is required of spatially-extensive and long-term blooming data in fruit trees to make up for insufficient information on regional-scale blooming changes and determinisms that are key to the phenological adaptation of these species. We therefore analysed blooming dates over long periods at climate-contrasted sites in Western Europe, focusing mainly on the Golden Delicious apple that is grown worldwide. On average, blooming advances were more pronounced in northern continental (10 days) than in western oceanic (6-7 days) regions, while the shortest advance was found on the Mediterranean coastline. Temporal trends toward blooming phase shortenings were also observed in continental regions. These regional differences in temporal variability across Western Europe resulted in a decrease in spatial variability, i.e. shorter time intervals between blooming dates in contrasted regions (8-10-day decrease for full bloom between Mediterranean and continental regions). Fitted sequential models were used to reproduce phenological changes. Marked trends toward shorter simulated durations of forcing period (bud growth from dormancy release to blooming) and high positive correlations between these durations and observed blooming dates support the notion that blooming advances and shortenings are mainly due to faster satisfaction of the heating requirement. However, trends toward later dormancy releases were also noted in oceanic and Mediterranean regions. This could tend toward blooming delays and explain the shorter advances in these regions despite similar or greater warming. The regional differences in simulated chilling and forcing periods were consistent with the regional differences in temperature increases.

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A comprehensive overview of the spatial and temporal variability of apple bud dormancy release and blooming phenology in Western Europe.

ADDITIONAL INDEX WORDS. rest, chilling requirements, apical dominance, Malus sylvestris ABSTRACT. The relative contribution of various temperatures to dormancy completion of lateral vegetative apple (Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.) buds was studied quantitatively on whole container-grown trees. Trees were exposed continuously to 10 different temperatures and also to daily alternating temperatures in a 24-hour cycle. In addition, fully chilled vertically and horizontally positioned shoots were compared under forcing conditions. No budbreak occurred in shoots chilled above 12.5 OC. There was a steep increase in budbreak as the chilling temperature fell from 12.5 to 7.5 OC. There was little difference in the level of budbreak on shoots chilled between 7.5 and 0 OC. The relative contribution of temperature to chilling accumulation in apple found in our study differs from what has been proposed for stone fruit and for apple in previous studies, especially at temperatures <6 OC. The length of exposure to forcing conditions required to initiate budbreak diminished as the chilling temperature was reduced. No additional bud- break was apparent on shoots chilled longer than 2100 chilling hours. The chilling requirement found here for lateral vegetative buds is much higher than that needed for terminal vegetative and flower buds. Trees that were exposed to daily alternating temperatures had lower levels of budbreak when the high temperature in the diurnal cycle was greater than 14 OC. Practically no budbreak was apparent on trees that were exposed to diurnal cycles with a high temperature of 20 OC for 8 hours. Budbreak on horizontally positioned trees was more than twice that on the vertically positioned trees, emphasizing the magnitude of the apical dominance effect and its strong masking of the chilling effect on lateral buds in vertically grown apple trees. Based on the data collected here we propose a new response curve for vegetative budbreak in 'Golden Delicious∑ apple, within a temperature range between 0 to 15 OC. Buds of most temperate-zone deciduous trees have a dormancy period in the winter. Low temperatures are the most significant fac- tor affecting dormancy completion, although, there are indications that heat, light intensity, and mist, during the endodormancy phase affect dormancy completion to a certain extent (Chandler, 1960; Erez et al., 1966; Erez et al., 1968; Freeman and Martin, 1981). Knowing the exact response of apple (Malus sylvestris var. do- mestica) buds to temperature is important for a basic understanding of dormancy and for the practical application of dormancy release or bloom delay techniques. Spring frost may cause severe damage to flowers and young foliage in temperate zones; therefore, predic- tion of the date of budbreak is an important issue for growers in those regions. Budbreak is affected by two temperature-dependent processes: a) the accumulation of chilling to the level required for dormancy completion; and b) the accumulation of the heat units required for the buds to develop to bloom and foliation. These two processes were shown to be interdependent, i.e., fewer degree-days of heating are required as the previously accumulated chilling in- creases (Couvillon and Erez, 1985a). In warm regions, temperatures in the winter are not low enough, or the duration of exposure is not

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Aharon Moshe

Papers

Temperature Effects on Dormancy Completion of Vegetative Buds in Apple