High-temperature tolerance by the endangered Mexican mayflower orchid, Laelia speciosa

Abstract

The Mayflower orchid, Laelia speciosa, is an endangered orchid endemic to oak forests of central Mexico. Because of extractive pressure on remaining natural populations, in vitro propagation has been proposed as an alternative for the massive propagation of this plant for conservation and commercial purposes. However, it is unknown whether this orchid will be able to tolerate the increased air temperature that is projected to occur during the present century, especially for in vitro propagated individuals at early developmental stages. A laboratory assay that measured electrolyte leakage, a common indicator of cell membrane integrity, was utilized to determine the high-temperature tolerance for 8-year-old individuals rescued from a wild population and for 2-year-old micropropagated individuals of the Mayflower orchid. The plants were incubated under day/night air temperatures of 25/15, 30/20, or 35/25 °C. Chlorophyll fluorescence measurements of the quantum yield of photosystem II (Fv/Fm) averaged 0.74 ± 0.01, except for the micropropagated individuals incubated under 35/25 °C, whose quantum yield of 0.64 ± 0.02 was indicative of stress. Electrolyte leakage also responded to incubation temperature. An observed increase of temperature tolerance of 0.6-1.0 °C per increased degree of incubation temperature indicates an ability to acclimate to rising air temperatures. However, the LT50 (the temperature that causes half of the maximum electrolyte leakage to occur) dramatically decreased (by 6.7-10.9 °C) for plants kept under 35/25 °C. In this case, the in vitro propagated individuals were less able to resist high air temperatures. It appears that the Mayflower will be able to survive climate change, provided that in vitro propagated individuals are sufficiently hardened.