Abstract
Recent climate change has resulted in warmer temperatures. Warmer temperatures from autumn to spring has negatively affected dormancy progression, cold (de)acclimation, and cold tolerance in various temperate fruit trees. In Japan, a physiological disorder known as flowering disorder, which is an erratic flowering and bud break disorder, has recently emerged as a serious problem in the production of the pome fruit tree, Japanese (Asian) pear (Pyrus pyrifolia Nakai). Due to global warming, the annual temperature in Japan has risen markedly since the 1990s. Surveys of flowering disorder in field-grown and greenhouse-grown Japanese pear trees over several years have indicated that flowering disorder occurs in warmer years and cultivation conditions, and the risk of flowering disorder occurrence is higher at lower latitudes than at higher latitudes. Susceptibility to flowering disorder is linked to changes in the transcript levels of putative dormancy/flowering regulators such as DORMANCY-ASSOCIATED MADS-box (DAM) and FLOWERING LOCUS T (FT). On the basis of published studies, we conclude that autumn–winter warm temperatures cause flowering disorder through affecting cold acclimation, dormancy progression, and floral bud maturation. Additionally, warm conditions also decrease carbohydrate accumulation in shoots, leading to reduced tree vigor. We propose that all these physiological and metabolic changes due to the lack of chilling during the dormancy phase interact to cause flowering disorder in the spring. We also propose that the process of chilling exposure rather than the total amount of chilling may be important for the precise control of dormancy progression and robust blooming, which in turn suggests the necessity of re-evaluation of the characteristics of cultivar-dependent chilling requirement trait. A full understanding of the molecular and metabolic regulatory mechanisms of both dormancy completion (floral bud maturation) and dormancy break (release from the repression of bud break) will help to clarify the physiological basis of dormancy-related physiological disorder and also provide useful strategies to mitigate or overcome it under global warming.
Highlights
Asian pears (Oriental pears), such as Japanese pear (Pyrus pyrifolia Nakai), Pyrus bretschneideri, and Pyrus ussuriensis, are cultivated worldwide, but mainly in east Asian countries including Japan and China
Global climate change from autumn to spring influences both flowering and dormancy in Rosaceae fruit trees. It is still unclear whether flowering disorder of Japanese pear results from abnormal flowering or abnormal dormancy or both. Because this disorder mainly occurs in reproductive organs but not or rarely in vegetative organs, we hereafter refer to this physiological disorder as “flowering disorder.”
The transcript level of DORMANCY-ASSOCIATED MADS-box (DAM) (MADS13-3), a dormancyrelated gene, increased in NTs on November 11 and from January 13 to February 3, showing a negative correlation with the depth of dormancy. No such correlation was detected in the flowering disorder trees” (FDTs). These results suggest that flowering disorder of FDTs may be caused by abnormal dormancy progression between the endodormancy and ecodormancy periods
Summary
Asian pears (Oriental pears), such as Japanese pear (Pyrus pyrifolia Nakai), Pyrus bretschneideri, and Pyrus ussuriensis (family Rosaceae), are cultivated worldwide, but mainly in east Asian countries including Japan and China. Since the 2000s, erratic flowering has occurred in Japanese pear trees in years with mild winters This has been observed in trees growing in greenhouses (irrespective of artificial heating) and in warmer regions (low latitudes) and in field-grown (open-air) trees. The symptoms of this disorder include delayed blooming, flower bud abortion, reduced number of florets, smaller size of flowers and peduncles, injured or dead flower buds, lack of uniformity in bud break and blooming, lower bud break rate of both floral and vegetative buds, and ultimate bud loss, especially in the basal parts of the long (succulent) shoots (Sugiura et al, 2010; Figure 2). In pome fruit trees in the Rosaceae, including Japanese pear, the tree bears floral buds at terminal and upper lateral positions of 1-year-old shoots These are mixed buds containing inflorescence and vegetative meristems and floral primordia. From floral initiation in summer and autumn until blooming in spring, robust mechanisms allow buds to align at a certain developmental stage, thereby preventing unexpected blooming until spring, and ensuring uniform blooming in spring
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