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 and uniformity:

• All introgression lines, recombinant inbreds or other prebred lines, as they tend to be weak, or partially dormant.

• Seed of the following wild species, L. cheesmanii (S. cheesmaniae), L. cheesmanii f. minor (S. galapagense), L. chilense (S. chilense), L. peruvianum (S. peruvianum, S. arcanum, S. cornelio-mulleri, S. huaylasense), 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. After bleaching, seed should be rinsed thoroughly, then sown directly (i.e. without redessication) in germination boxes or in soil.

   In addition to bleaching, seed may also be encouraged to sprout by knicking 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. We recommend knicking after the bleaching step.

   Germination boxes and paper can be obtained from: www.hoffmanmfg.com and www.seedpaper.com/seedpapers.htm

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 95° 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.