Author
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Foley, Michael |
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Submitted to: Leafy Spurge News
Publication Type: Trade Journal Publication Acceptance Date: 9/18/2005 Publication Date: 10/1/2005 Citation: Foley, M.E. 2005. Seed dormancy in leafy spurge. Leafy Spurge News. XXVII(1):2. Interpretive Summary: Leafy spurge reproduces asexually via crown and root buds and sexually by seeds. Our unit has largely focused on dormancy in buds and vegetative reproduction. However, dormant seeds in the soil play a key role in the persistence of weeds. For example, leafy spurge seeds can remain dormant and viable in the soil from three to eight years. I designed an experiment to answer two questions: What type of dormancy occurs in leafy spurge seeds and what environmental conditions shift the seeds from a dormant to non-dormant state? There are two main types of seed dormancy: Embryo-imposed and seed covering-imposed. Our investigations revealed that removal of the hard seed coat surrounding the endosperm and embryo caused rapid germination. Removal of the soft nutrient-containing endosperm tissue from around the embryo did not increase the rate of germination. Therefore, leafy spurge displays covering-imposed dormancy due to a hard seed coat. To examine what environmental conditions facilitate afterripening, that is “breaking dormancy”, we exposed seeds to warm, dry; warm, moist; cool, dry; and cool, moist conditions for periods of 12 and 24 weeks. Seeds harvested in one year afterripened best under warm-moist conditions, while seeds harvested in a second year responded nearly the same to both warm- and cool-moist conditions. In addition, 24 weeks of afterripening, followed by 21 days of incubation in water, was required to break dormancy and achieve nearly complete germination, respectively. The mixed response to temperature under moist conditions, relatively long duration of afterripening to break dormancy, and protracted incubation to complete germination, suggests we have yet to determine what environmental conditions or factors facilitate germination of hard-seeded leafy spurge. Follow-up studies should focus on defining environmental factors or conditions that weaken or break the seed coat and environmental and genetic factors that provide leafy spurge seeds with a hard coat. Unit scientists have been discussing how we might use the genomic tools (i.e., expressed sequence tag database and microarrays) that we are developing, in follow-up studies. As with all our research, the goal is to provide new biological insights that will give rise to practical ways to manage weeds. Technical Abstract: Leafy spurge reproduces asexually via crown and root buds and sexually by seeds. Our unit has largely focused on dormancy in buds and vegetative reproduction. However, dormant seeds in the soil play a key role in the persistence of weeds. For example, leafy spurge seeds can remain dormant and viable in the soil from three to eight years. I designed an experiment to answer two questions: What type of dormancy occurs in leafy spurge seeds and what environmental conditions shift the seeds from a dormant to non-dormant state? There are two main types of seed dormancy: Embryo-imposed and seed covering-imposed. Our investigations revealed that removal of the hard seed coat surrounding the endosperm and embryo caused rapid germination. Removal of the soft nutrient-containing endosperm tissue from around the embryo did not increase the rate of germination. Therefore, leafy spurge displays covering-imposed dormancy due to a hard seed coat. To examine what environmental conditions facilitate afterripening, that is “breaking dormancy”, we exposed seeds to warm, dry; warm, moist; cool, dry; and cool, moist conditions for periods of 12 and 24 weeks. Seeds harvested in one year afterripened best under warm-moist conditions, while seeds harvested in a second year responded nearly the same to both warm- and cool-moist conditions. In addition, 24 weeks of afterripening, followed by 21 days of incubation in water, was required to break dormancy and achieve nearly complete germination, respectively. The mixed response to temperature under moist conditions, relatively long duration of afterripening to break dormancy, and protracted incubation to complete germination, suggests we have yet to determine what environmental conditions or factors facilitate germination of hard-seeded leafy spurge. Follow-up studies should focus on defining environmental factors or conditions that weaken or break the seed coat and environmental and genetic factors that provide leafy spurge seeds with a hard coat. Unit scientists have been discussing how we might use the genomic tools (i.e., expressed sequence tag database and microarrays) that we are developing, in follow-up studies. As with all our research, the goal is to provide new biological insights that will give rise to practical ways to manage weeds. |
