Seed germination in Ormosia macrocalyx, an endangered tropical forest tree

Abstract

<p><strong>Background </strong><em>Ormosia macrocalyx</em> is a tropical forest tree classified as endangered. Its seeds experience problems of dispersion and apparent physical dormancy due to their hard seed coating.</p><p><strong>Hypotheses </strong>1) The stages of dehiscence of the fruits of <em>Ormosia macrocalyx</em> influence the germinative behavior of its seeds. 2) Pregerminative treatments will improve the germination process of the seeds stored under refrigeration.</p><p><strong>Study species</strong> <em>Ormosia macrocalyx </em>Ducker.<em></em></p><p><strong>Study site and period </strong>Villahermosa, Tabasco, Mexico from October 2012 to October 2014.<strong></strong></p><p><strong>Methods </strong>Two completely randomized experiments were conducted in order to analyze the germination process by 1) evaluating germination in seeds from fruit at three stages of dehiscence (closed, semi-open, and open fruit) and 2) applying four treatments, including three pregerminative treatments (water soaking for 24 h, mechanical scarification and scarification+1 % gibberellic acid) plus an untreated control, to seeds stored under refrigeration for 17 months.</p><p><strong>Results</strong> Differences were found in germination rate (GR), corrected germination rate (CGR) and time to attain 50 % germination (T₅₀) among treatments in the first experiment, with the seeds from open fruits presenting the lowest response (3.31 % day^-1 for GR and CGR, and 15.8 days for T₅₀), although all treatments showed similar times for the initiation of germination (GI) and final germination percentage (GP). In the second experiment, the effect of scarification was greater than both the control and soaking treatments. Scarification treatment values were 68.0 % (GP), 12.0 days (GI), 4.53 % day^-1 (GR), 6.65 (CGR) and 14.5 days (T₅₀). Addition of gibberellic acid did not produce any further advantage over scarification alone.</p><p><strong>Conclusions</strong> Seeds from open fruits have lower germination rates, although the final GP is not affected. Stored seeds present physical dormancy but lose viability with storage and, when collected after remaining attached to the tree for undefined periods, scarification can greatly improve their germination rate. </p>