In vitro, symbiotic germination of Platanthera species for conservation efforts
Ashley Clayton and Peter Zale, Longwood Gardens
At the Valmont Bog in Hazelton, PA, there are populations of three, state-listed taxa of Platanthera: P. ciliaris, P. blephariglottis, and P. xbicolor, a natural hybrid of the other two species. They are threatened by forest succession, climate change, silt-laden runoff, and herbicide spraying. However, as is the case for most native orchids, conservation efforts are hindered by limited propagation information. To support in situ and ex situ conservation of these species, this experiment was designed to determine the most effective mycorrhizal fungi for in vitro germination of each taxon. In August 2018, pelotons were isolated from the roots of each species and maintained in culture. Multiple capsules from each orchid species were then collected the following month. Seeds were surface sterilized in a 10% bleach solution for 18 minutes and rinsed with distilled water. They were plated on an agar-based medium containing powdered Liriodendron tulipifera wood and inoculated with one of the three fungal isolates. Visual inspection showed that at least 71% of seeds on each plate contained healthy embryos except for seeds originating from one capsule of P. xbicolor, which only about a third had embryos. Visual observation also revealed an association between the hyphae and the rhizoids of protocorms. The peak germination occurred between four and five weeks after sowing. After seven weeks, seed germination ranged from 0 to 27%. Compared to a previous preliminary experiment, the addition of mycorrhizae decreased the time of peak germination from several months to about one month. The effect of each mycorrhiza on germination percentage and protocorm development is still being determined.