Peter Zale and Matt Taylor, Longwood Gardens
Several species of Spiranthes native to the Eastern U.S. are considered rare, threatened or endangered by federal and state agencies. Using the Pennsylvania endangered Spiranthes casei as a model species, experiments were designed to determine optimal conditions for in vitro seed germination and seedling development. Seeds were collected in November 2015 from 10 individual plants found in three subpopulations in Elk and McKean counties, Pennsylvania, and air-dried for six weeks. Seeds were surface sterilized for 10 or three minutes in a 10% bleach solution, then plated onto a commercially available terrestrial orchid seed germination media: P723, M551 or K400 (Phytotechnology Labs, Shawnee Mission, KS) with 5 replicate plates. Seed germination ranged from 24 to 60 % and occurred on all three media only with the 3-minute treatment. None of the seeds treated with bleach for 10-minutes germinated and visual inspection revealed badly damaged embryos. After shoot initiation, 150 seedlings were transferred to individual test tubes on one of two media (P723 or P658) and each was given one of the three 24-hour light/dark photoperiod treatments for 10 months: 24/0, 18/6, or 0/24. Seedling survival and growth occurred in all treatments, but seedlings on P723 with the 24/0 or 16/8 photoperiod treatments had a significantly greater fresh weight, leaf length, number of roots and root length than light treatments on P658 and dark treatments. Results indicate Spiranthes seeds can be damaged by extended chemical scarification times and the light is essential for optimal seedling growth.