Seed dormancy breaking of temperate region deciduous tree species

Kidd, Mark and Roberts, Mike (2021) Seed dormancy breaking of temperate region deciduous tree species. Masters thesis, Lancaster University.

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Abstract

Tree seeds often exhibit dormancy and require several months of moist chilling (cold stratification) before germination can proceed. Seed dormancy is poorly understood with no clear identified mechanism as to why cold stratification works. Endogenous plant hormones and chemicals have been implicated in this process. The requirement for a lengthy cold stratification period (often 2-4 months) limits the popularity of growing trees from seed in the amateur gardening market and reduces productivity for professional tree growers. A treatment product or protocol which breaks dormancy would address these issues. We have been able to define the seed dormancy status of a range of temperate region tree species. The deeply physiologically dormant seeds of Acer tataricum (tartar maple) were chosen as a test seed species. It was determined that water and oxygen permeability of the seed coats were not a major factor in maintaining dormancy in this seed. Nor was the oxygen concentration that the seed was incubated in. There was also no indication of inhibitory substances (to germination of lettuce seeds) within the seed. The testa of A. tataricum was found to weaken over time after imbibition in both cold and warm conditions and it's physical restriction of the embryo is likely to be a secondary factor in prolonging dormancy. It was found that cytokinins can break the dormancy of A. tataricum. A treatment for breaking the dormancy in temperate region tree seeds is proposed using a 350 mg/l kinetin/20% dimethylsulphoxide solution. This treatment successfully removed the dormancy and substituted for up to 3 months of cold stratification in these species in Acer platanoides (Norway Maple 'Crimson King') and Tilia cordata (Small-leaved Lime). It also increased the germination percentage of Acer pseudoplatanus (Sycamore). Possible mechanisms of how cold stratification breaks dormancy in relation to this finding are discussed. Other species and varieties of dormant seed respond to other plant hormones such as A. platanoides to jasmonic acid. Future areas of study in order to understand the mechanism of dormancy release are suggested along with further ideas to develop a dormancy breaking seed treatment.