LIGHT ENHANCEMENT OF SYMBIOTIC SEED-GERMINATION AND DEVELOPMENT OF ANENDANGERED TERRESTRIAL ORCHID (PLATANTHERA-INTEGRILABIA)

Seeds of an endangered orchid, Platanthera integrilabia, were exposed to one of three light treatments: 7 days initial darkness followed by 16 h per day photoperiods, 16 h per day photoperiods for 7 days follow ed by darkness, and 16 h per day photoperiods. Alternatively, a contin uous dark treatment in symbiotic and asymbiotic culture was provided. Seeds exposed to 16 h per day photoperiods or an initial 7 days of dar kness followed by 16 h per day photoperiods were largely inhibited fro m germinating. Seeds exposed to 16 h per day photoperiods during the f irst 7 days after fungal inoculations followed by darkness had a signi ficantly higher percent germination than the other treatments, includi ng those in continuous darkness. Seedling (protocorm) development (i.e ., formation of leaf primordia) was also enhanced by initial light com pared to seedlings under continuous darkness. We speculate that light exposure followed by darkness occurs naturally starting with the shedd ing of seeds from capsules to their immersion in a substrate where ger mination occurs. The beneficial effects of light in this study argues in support of light usage to stimulate germination and seedling develo pment of temperate terrestrial orchids.