Journal Article

Desiccation tolerance, longevity and seed-siring ability of entomophilous pollen from UK native orchid species

Timothy R. Marks, Philip T. Seaton and Hugh W. Pritchard

in Annals of Botany

Published on behalf of The Annals of Botany Company

Published in print July 2014 | ISSN: 0305-7364
Published online July 2014 | e-ISSN: 1095-8290 | DOI: https://dx.doi.org/10.1093/aob/mcu139
Desiccation tolerance, longevity and seed-siring ability of entomophilous pollen from UK native orchid species

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Background and Aims

Pollinator-limited seed-set in some terrestrial orchids is compensated for by the presence of long-lived flowers. This study tests the hypothesis that pollen from these insect-pollinated orchids should be desiccation tolerant and relatively long lived using four closely related UK terrestrial species; Anacamptis morio, Dactylorhiza fuchsii, D. maculata and Orchis mascula.

Methods

Pollen from the four species was harvested from inflorescences and germinated in vitro, both immediately and also after drying to simulate interflower transit. Their tolerance to desiccation and short-term survival was additionally assessed after 3 d equilibration at a range of relative humidities (RHs), and related to constructed sorption isotherms (RH vs. moisture content, MC). Ageing of D. fuchsii pollen was further tested over 2 months against temperature and RH, and the resultant survival curves were subjected to probit analysis, and the distribution of pollen death in time (σ) was determined. The viability and siring ability, following artificial pollinations, were determined in D. fuchsii pollen following storage for 6 years at –20 °C.

Key Results

The pollen from all four species exhibited systematic increases in germinability and desiccation tolerance as anthesis approached, and pollen from open flowers generally retained high germinability. Short-term storage revealed sensitivity to low RH, whilst optimum survival occurred at comparable RHs in all species. Similarly, estimated pollen life spans (σ) at differing temperatures were longest under the dry conditions. Despite a reduction in germination and seeds per capsule, long-term storage of D. fuchsii pollen did not impact on subsequent seed germination in vitro.

Conclusions

Substantial pollen desiccation tolerance and life span of the four entomophilous orchids reflects a resilient survival strategy in response to unpredictable pollinator visitation, and presents an alternative approach to germplasm conservation.

Keywords: Anacamptis morio; Orchis mascula; Dactylorhiza maculata; Dactylorhiza fuchsii; orchid pollination; pollen germination; storage; longevity; desiccation tolerance; seed-set; entomophilous pollen

Journal Article.  6746 words.  Illustrated.

Subjects: Plant Reproduction and Propagation

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