Improving Seed Germination using Bleach
We recommend that seed of the following types of tomato accessions
be treated with bleach (see protocol below for details) to improve germination rate
All introgression lines, recombinant inbreds or other prebred lines,
as they tend to be weak, or partially dormant.
Seed of the following wild species: S. cheesmaniae, S. galapagense, S. chilense,
S. peruvianum, S. arcanum, S. corneliomulleri,
S. lycopersicoides, S. sitiens, S. juglandifolium, S. ochranthum.
Seed of the other
wild species often benefit from bleach treatment as well.
Weak or slow mutants.
Any seed older than 10 years or stored under suboptimal conditions.
Any other tomato
seed that does not germinate well without treatment.
For general use, seeds are soaked
in 2.7% sodium hypochlorite (half-strength standard household bleach) for 30 min. (60 min. for S. cheesmaniae, S. galapagense, S. ochranthum, and S. juglandifolium).
After bleaching, seed should be rinsed thoroughly, then sown directly (i.e. without allowing to dry) in germination boxes or in soil.
In addition to bleaching, it is sometimes beneficial to knick
the seed coat near the radicle end using a sharp scalpel. Though not practical for
large seed samples, knicking may be worth while for very weak seed and/or when seed
quantities are extremely limited. Knicking should be done after the bleaching step.
Germination boxes and paper can
be obtained from: www.hoffmanmfg.com and
www.seedpaper.com/seedpapers.htm . For best results we prefer the 4-5/16" x 4-5/16" x 1-3/8" OD plastic boxes, with the Steel Blue Blotter paper. For large numbers of samples, such as for germination tests, we use the Regular Weight Germination Papers, and Noblot Indelible Pencils to record sample numbers.
A METHOD FOR IMPROVING SEED GERMINATION OF SOLANACEOUS SPECIES
C. M. Rick and F. H. Borgnino
Our most notorious problem is with
L. cheesmanii, seeds of which
will not germinate for us without pretreatment, no matter what the age of seeds, temperature regime,
soil mixture, or other conditions of sowing. Seeds of certain accessions of
L. chilense, L. hirsutum, L. peruvianum, S. lycopersicoides,
and S. juglandifolium are also refractory, although a small percentage
often sprout without special measures. The germination of seeds of any species that are old or
otherwise in poor condition can likewise benefit. Such pretreatments as vernalization, sulfuric
acid, gibberellic acid, high temperatures, and other stresses were applied to cheesmanii seeds
without success. It finally became apparent that the dormancy is vested in the seed coats,
the virtual removal of which is essential to sprouting. Laborious chipping of the seed coat with
a sharp scalpel provided the clue. Passage through the gut of Galapagos tortoise is more effective,
but cumbersome, nasty, and otherwise too inconvenient for general use. The
method finally adopted is commonly used by agronomists for seeds of
certain cantankerous legumes.
For general use, seeds are soaked
in 2.7% sodium hypochlorite (half-strength standard household bleach) for
30 min, then thoroughly rinsed in tap water and sown directly or dried for
sowings within the next few days. A single treatment hardly ever suffices
for cheesmanii seeds, which must be treated at weekly intervals for
as long as two months. The entire testa may thereby be removed, but the
endosperm and embryo appear to withstand such seemingly violent treatment.
These repeated applications cannot be applied, of course, to seeds planted
directly in soil. Instead, we incubate the seeds on moist blotting paper
in plastic sandwich boxes or any other suitable transparent container. The
boxes are kept in an illuminated incubator maintained at 25°C day, 18°C
night temperatures, but ordinary room conditions are satisfactory. Keeping
the seeds in the dark until sprouted seems to be advantageous. When the
seeds have germinated and the cotyledons are well developed, the seedlings
are transplanted to nursery flats filled with sterilized soil and placed
in partial shade in the greenhouse.
For more information:
Rick, C.M., and R. I. Bowman (1961) Galapagos tomatoes and tortoises. Evolution 15: 407-417
Rick, C.M., and D. Hunt (1961) Improved seed germination with the use of sodium hypochlorite. Report of the Tomato Genetics Cooperative 11: 22.