Seed Dormancy
Introductory concepts
Dormancy
- 1: A state in which viable seeds (or buds; spores) fail to germinate under conditions of
moisture, temperature and oxygen favorable for vegetative growth
2: A state of relative metabolic quiescence
Dormancy can be seen as "dispersal in time"
Dispersal phase usually dormant; dehydrated seeds weight less (esp. wind dispersal) and
are metabolically slower
Dormancy:
- -rhythmic adaptation of weeds to the temporal rhythms in the environment
-strategic alternative to dispersal
Somatic Polymorphism and Dormancy
Production of seeds of different morphologies or behavior (phenotypes) on different
parts of the same plant
Seed somatic polymorphism represents an allocation of different fractions of the seed
output of a plant to different ends (different germination requirements)
- -adaptive advantage to producing seed on one plant with different qualities
-seed dormancy somatic polymorphism is common in weedy species of Gramineae, Compositae,
Chenopodiaceae and Cruciferae families
-somatic polymorphism allows sensitive adjustment to environment in the number of morphs
it produces
Seed and dormancy polymorphisms are so common amongst weed species that it is dangerous
to ascribe one set of dormancy mechanisms or germination breaking requirements to any one
species
Seed somatic polymorphism examples:
Example: Rumex crispus (curled dock)
- -progeny of individual plants vary enormously in ability to germinate in darkness or at
common temperature
-variation is greater between plants than between habitats, no one germination response
Example: Xanthium spp. (common cocklebur);
- -seed borne in pairs in capsule: large and small seed dispersed together
-upper seed in capsule usually dormant, lower germinates first
-dormancy breaking requirements different for 2: 12 month difference insurance second will
become established if first year unfavorable
Example: Avena fatua (wild oat), and Avena ludoviciana
- -grains borne on different parts of the spikelet have different germination requirements
-first grain of spikelet lacks dormancy, remainder have deep dormancy
Example: Compositae germination behavior differentiated by seed size, seed formed in
ray versus disc flowers
Example: Chenopodium album (common lambsquarters) may produce 4 different kinds
of seed on same plant
- -two color categories: brown and black; two seed coat categories: reticulate and smooth
-brown: thin-walled, larger, germinate quicker than black, even at low temperatures;
killed by winter, but if they survive have the capacity to produce very large plants with
high reproductive output; only 3% of seed on a plant; among the first to be produced by a
plant
-black: require cold treatment, nitrate to break dormancy
-ratio of brown:black govered by environmental conditions
Example: common purslane seed varies from nondormant to dormant on same plant)
