Effects of development, temperature, and calcium hypochlorite treatment on in vitro germinability of Phalaenopsis seeds

Abstract

There are no standardized procedures for sanitizing orchid seeds for propagation by tissue culture and there is insufficient information about the optimum stage of orchid seed development for best germination. Phalaenopsis amabilis flowers were hand-pollinated and fruits harvested 90, 105, and 120 d after pollination (DAP) for seed developmental analysis. Embryo cell number per seed was counted after staining with 4′-6-diamidino-2-phenylindole and viewing through a confocal microscope. Germination percentage and cell number per embryo increased from 14 to 61% and 41 to 66%, respectively, during fruit development from 90 to 120 DAP. Seeds from mature, browning (∼140 DAP) Phalaenopsis Sogo Lit-Angel and Phalaenopsis spp. breeding line 9450 seed pods failed to germinate until frozen at -196, -80, or -18 °C and thawed or chilled at 4 °C for 10 d. Germinability in 140 DAP seeds was correlated with cracked testa after freezing and thawing. P. amabilis seeds were treated with 0, 5, 10, or 15% calcium hypochlorite (CH) for 5, 10, or 15 min. Ninety six percent of untreated seeds from 90 DAP fruit produced protocorms within 40 d after sowing (DAS). Exposing seeds to 5% CH for 10 or 15 min decreased germination to 85 and 73%, respectively. Exposure to 10 or 15% CH for 5, 10, or 15 min produced seed germination percentages of less than 40%. Protocorms developed root hairs and shoot primordia by 50 DAS and an average of one leaf and root by 85 DAS after treatment with either 0 or 5% CH. Higher concentrations delayed or inhibited protocorm development. Green fruits 120 DAP produced the highest percentage of protocorms, while ∼140 DAP seeds from browning fruit were dormant but cold treatments increased germination. © 2008 Elsevier B.V.