Handbook of Plant and Crop Physiology

GERMINATION AND EMERGENCE 65

Some seeds may lose their requirement for

light after dry storage.

Most common in temperate herbaceous plant.Most common in temperate trees and shrubs.

Abnormal development of unchilled deepdormant seeds includes enlargement andgreening of the cotyledons, short thickradicles, no epicotyl growth, abnormalroots, physiological dwarfing.

In nature, or when sown outdoors, such seeds

require at least two full growing seasons tocomplete germination.

Thermal dormant seeds will not germinate

without treatment when temperaturesbecome lower.

Conditions include unfavorably high or low

temperatures, water stress, prolonged lightor darkness. Important survival adaptationfor seeds in nature but less so incultivation

Expose to light (positive photodormancy)

or darkness (negative photodormancy).

Moderate periods of moist chilling



2

months.

Long periods of moist chilling



2

months; gibberellic acid.

Eliminate dormancy conditions in proper

sequence.

Warm to induce embryo development,

then cold to eliminate physiologicaldormancy.

Warm to induce initial germination and

growth of radicle and hypocotyl, thencold to release epicotyl dormancy.

Cold followed by warm for radicle

growth, then another cold period torelease epicotyl dormancy.

Scarify then moist chill.Moist chilling; growth regulators.Chilling or warm treatment.

PhotodormantEmbryo germinates if seed coat removed.Embryo usually will not germinate if seed

coat removed or will developabnormally.

Combinations of two or more types of

primary dormancy; separate dormancyconditions for different parts of theembryo.

Underdeveloped embryos plus

physiological dormancy.

Epicotyl dormant; radicle and hypocotyl

nondormant.

Both epicotyl and radicle dormant.Example: seed coat dormancy plus

intermediate/deep physiologicaldormancy.

Induced by germination environment

although seed itself not dormant.

High temperatureUnfavorable seasonal conditions.

IntermediateDeep

3. Double or combinational

MorphologicalSimple Epicotyl Exo-endodormancy

B. Secondary1. Thermodormancy2. ConditionalSource

: Adapted from Refs. 8 and 24.