Abstract
The initiation, progression, and natural variation of autumn senescence in European aspen (Populus tremula) was investigated by monitoring chlorophyll degradation in (1) trees growing in natural stands and (2) cloned trees growing in a greenhouse under various light regimes. The main trigger for the initiation of autumn senescence in aspen is the shortening photoperiod, but there was a large degree of variation in the onset of senescence, both within local populations and among trees originating from different populations, where it correlated with the latitude of their respective origins. The variation for onset of senescence with a population was much larger than the variation of bud set. Once started, autumn senescence was accelerated by low temperature and longer nights, and clones that started to senescence late had a faster senescence. Bud set and autumn senescence appeared to be under the control of two independent critical photoperiods, but senescence could not be initiated until a certain time after bud set, suggesting that bud set and growth arrest are important for the trees to acquire competence to respond to the photoperiodic trigger to undergo autumn senescence. A timetable of events related to bud set and autumn senescence is presented.
Highlights
The initiation, progression, and natural variation of autumn senescence in European aspen (Populus tremula) was investigated by monitoring chlorophyll degradation in (1) trees growing in natural stands and (2) cloned trees growing in a greenhouse under various light regimes
Useful materials to meet these objectives include appropriate germplasm resources for phenotypic evaluations of the trait(s) of interest and a reliable set of candidate genes, since we have shown that association mapping is a powerful technique for identifying the genetic bases, down to single nucleotides, that may be responsible for phenotypic variations in aspen (Ingvarsson et al, 2008)
The plant materials used included a free-growing aspen tree at the Umea University campus described in several previous works (Bhalerao et al, 2003; Andersson et al, 2004; Keskitalo et al, 2005), the Swedish aspen (SwAsp) collection of genotypes sampled throughout Sweden (Ingvarsson et al, 2006; Hall et al, 2007; Luquez et al, 2008), and a local population of aspen from the Umearegion
Summary
The initiation, progression, and natural variation of autumn senescence in European aspen (Populus tremula) was investigated by monitoring chlorophyll degradation in (1) trees growing in natural stands and (2) cloned trees growing in a greenhouse under various light regimes. We would like to identify the genes that regulate autumn senescence in aspen and the alleles that are responsible for their adaptation to northern climates. To achieve this goal, we need better understanding of the mechanisms that initiate senescence in. We need to elucidate (1) the interactive effects of photoperiod and temperature changes on the induction and progression of senescence and (2) the relationship between the timing of bud set/growth cessation and the initiation of autumn senescence. The plants were examined in a series of experiments under both controlled and natural conditions
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