TOW: Dormancy, Seed and Bulb

Roy M. Sachs
Sun, 11 Jan 2004 17:33:14 PST
Dormancy is one of the terms used to describe a state of seeds, bulbs 
and buds when they do not grow even though environmental conditions 
are otherwise favorable for growth. As a TOW the subject of dormancy 
will be divided into two parts, a) dormancy in seed and b) in bulbs.

SEED. Most seed during, and for sometime after, formation in fruit do 
not germinate and some require special treatments that will be 
considered below.

After-ripening is the time between the formation of a mature seed and 
its ability to germinate; in some species there is no after-ripening 
period and seed germinate in the fruit (a highly undesirable feature 
in most edible fruit where the germinating seed resemble large white 

I have observed that seed of some freesia and alstroemeria  taken 
from green fruit rarely germinate,  but they do fairly quickly when 
taken from dried fruit.  Thus the after-ripening period is satisfied 
in the fruit as it dries.  But there may be other cases where 
germinability increases for some period during seed storage.  Forum 
members can help here.

Immature embryo. Seed of many orchids do not germinate unless 
provided with a medium that nurtures embryo development, without at 
the same time nurturing the development of fungi and bacteria.  We 
know that orchid seed propagation in sterile culture is a major 
horticultural industry, but I don't know of other geophyte 
species/genera where immature embryos are commonly produced (certain 
hybrids aside, where embryos must be removed from an apparent 
inhibiting influence of the endosperm).

Impermeable/Mechanically Resistant Seed Coats. Many legumes and some 
grasses have very hard, mechanically resistant, or gas or water 
impermeable, seed coats. How many geophytes have seed that fall in 
this category? Is the problem solved by a brief treatment in strong 
acid, by nicking the seed coats with a scalpel, rolling them in emery 
cloth, etc? These are the measures that classroom teachers employ to 
eliminate the seed coat as the barrier to germination.

The forum has had several reports from members who recommend not 
giving up on seed that don't germinate quickly, even in a year or 
two, and I suspect that they're waiting for the seed coats to be 
digested or weakened by weathering or soil-borne bugs (microbial and 

Physiological dormancy. There are embryos that will not grow  for 
internal, mostly unknown, reasonsÅ ..this is often termed, 
physiological dormancy.

Methods of breaking physiological dormancy:

Chilling. Germination in most alstroemeria  is hastened by a 3 to 4 
week  chilling treatment following imbibition. This is not an 
uncommon requirement for seed, but I have not been able to find 
references for other species, particularly in the literature on 
breeding of bulbs or seed producers where breaking seed dormancy 
would be emphasized. Hopefully, forum members, particularly seed 
suppliers, will be able to contribute specific information.

Leaching of seed, say for 24 hours, also works well to promote 
germination in some seed that contain water soluble inhibitors. These 
are mostly phenolic compounds that turn the leachate brown.  I 
suspect that seed-borne inhibitors might be quite common. Work with 
lower Mojave desert annuals showed that germination, following 
precise amounts of rain, is related to leaching of inhibitors. Some 
of the recommendations for floating seed on water may promote 
leaching of inhibitors.

Although I have not shown that leaching is necessary in alstroemeria 
I do soak them for 24 hours to ensure imbibition and in the process I 
remove a lot of phenolics as shown by the dark-brown leachate.

Growth Regulators. Gibberellic acid and relatives promote germination 
of many seed, but I've seen nothing specific for geophytes, nor have 
i seen literature on applications of cytokinins or ethylene that 
would apply to us.  We need help from PBS members who have been 
successful with growth regulators.

I tried gibberellic acid treatments on alstroemeria seed since some 
of the  species of interest seemed slow to germinate or had low 
germination percentage; although there was more rapid (but not 
desirable) elongation of the emerging shoot; at least in the small 
trials that I ran there was no improvement in germination percentage 
so I discontinued the trials.

Light promotes the germination of some seed and slows the germination 
of others, but once more I've seen nothing of interest regarding 
geophytes. As a routine I bury all seed with approximately one inch 
(2+ cm) of the perlite:///vermiculite/ mix that I use for germination and 
have observed no difficulties.

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