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weed seed dormancy ppt

Somatic polymorphism: Production of seeds of different morphologies or behavior (phenotypes) on different parts of the same plant; not a genetic segregation but a somatic differentiation

Breaking Dormancy
Block to Dormancy
Dormancy Trigger
Biochemical Trigger
Dormancy Switch
Switch for Germination

In this unit we will learn the established model of seed germination and dormancy. We will also discuss how a better model might be developed. Warning signs that you are headed in the wrong direction in your thinking can be signaled by the following terms, often used. BEWARE!:

Enforced Dormancy

After-ripening: period after dispersal when the seed, spores and bud cannot germinate, even under favorable conditions, and during which changes occur allowing it to germinate.

2. Often this trigger is a seasonally related stimulus which can switch on germination at an adaptively appropriate time of year

Reading assignment: Harper: Ch. 3: pp. 61-82; summary p. xiv-xv

2. Dormancy caused by mechanical restriction of growth by embryo coverings (pericarp, testa, perisperm, endosperm)
-example: cocklebur: upper seed (of two in capsule) radicle is restricted, insufficient thrust to rupture testa and germinate

The weed seedbank is the reserve of viable weed seeds present on the soil surface and scattered in the soil profile. It consists of both new weed seeds recently shed and older seeds that have persisted in the soil for several years. Agricultural soils can contain thousands of weed seeds per square foot and understanding the factors impacting the dynamics of weed seedbanks can help in the development of integrated weed management (IWM) programs. Instead of solely considering crop yield loss, management could also include strategies to deplete the weed seed bank.