Factors affecting germinable seed yield in Cypripedium calceolus var. pubescens (Willd.) Correll and Epipactis helleborine (L.) Crantz (Orchidaceae)

Abstract

One of the challenges facing orchid conservationists is to get a betterunderstanding of seed parent fecundity. This can be especially laboriousfor orchids whose seed is difficult to germinate. Mature seeds ofCypripedium calceolus var. pubescens (Willd.) Correll (Orchidaceae) havebeen reported to require 8 weeks pre-chilling at 4 degrees C and afurther month at 20 degrees C to induce germination, but seedsprematurely harvested at 7-8 weeks post-pollination germinateasymbiotically without chilling in less than 1 month. Mature seeds ofEpipactis helleborine (L.) Crantz (Orchidaceae) have also presented achallenge but the identification of plants whose seeds are quick andeasy to germinate has provided us with a tool to study patterns ofproduction of this seed class. Preliminary field experiments suggestthat timing of pollination in these two taxa is critical for thedevelopment of seed. When seeds from capsules of C. calceolus var.pubescens harvested 7 weeks after pollination were examined, theproportion of fully mature embryos increased with increasinganthesis-pollination interval over the first 10 days. Paired flowersfrom five genets xenogamously hand-pollinated at 2-day intervals fromthe second day after anthesis until the flowers wilted weresignificantly less likely to produce fruits as the flowers aged but theflower age at which this occurred varied between genets. Thegerminability of seeds from different pollen and seed parentcombinations was tested on eight different media formulations and over arange of post-anthesis and post-pollination intervals. Different agedseeds germinated variably, the post-anthesis interval being the mostreliable predictor of germination outcomes. Intercrossing of plants ofC. calceolus var. pubescens suggests that seed production andgerminability are maternally mediated traits. With E. helleborine,germinable seed can be produced bath by self-and by cross-pollination ofselected plants but we have observed an influence of flower position inthe inflorescence on self-compatibility and on the production of theeasy-to-germinate seed class. The timing of pollination in these twounrelated orchids has a considerable influence upon seed production andseed quality in plants of established fecundity. These findings suggestthat flower age at pollination must he considered when interpretingsimilar studies in the Orchidaceae. (C) 1998 The Linnean Society ofLondon.