High-throughput sequencing of African chikanda cake highlights conservation challenges in orchids

Sarina Veldman,Aline Nieman,Florent Martos,Barbara Gravendeel,Tinde R Van Andel,Benny Bytebier,Youri Lammers,Grace Ngugi,Joseph N Otieno,Hugo J De Boer,Elza Duijm

doi:10.1007/s10531-017-1343-7

Abstract

Chikanda is a traditional dish made with wild-harvested ground orchid tubers belonging to three orchidioid genera, Disa, Satyrium and Habenaria, all of which are CITES appendix II-listed. Identification of collected orchid tubers is very difficult and documentation of constituent species in prepared chikanda has hitherto been impossible. Here amplicon metabarcoding was used in samples of six prepared chikanda cakes to study genetic sequence diversity and species diversity in this product. Molecular operational taxonomic unit identification using similarity-matching reveals that species of all three genera were present in the chikanda samples studied. Disa was present in all of the samples, Satyrium in five out of six and Habenaria in one of the samples, as well as a number of other plants. The fact that each sample contained orchids and the presence of a wide variety of species from all genera in this traditional dish raise serious concerns about the sustainability of this trade and the future of wild orchid populations in the main harvest areas. This proof-of-concept study shows that Ion-Torrent PGM is a cost-effective scalable platform for metabarcoding using the relatively long nrITS1 and nrITS2 regions. Furthermore, nrITS metabarcoding can be successfully used for the detection of specific ingredients in a highly-processed food product at genus level, and this makes it a useful tool in the detection of possible conservation issues arising from commercialized trade or processed plant products.

Highlights

Chikanda is a traditional dish that consists primarily of wild-harvested terrestrial orchid tubers and peanuts (Davenport and Ndangalasi 2001)
Despite the fact that all orchids are CITES appendix II listed (2014), and their international trade is subject to specific rules and permits, an estimated 2.2–4.0 million orchid tubers are illegally exported from Tanzania to Zambia each year, and a total of 85 terrestrial orchid species are identified to be at risk of overharvesting (Davenport and Ndangalasi 2003; Veldman et al 2014)
If reads are clustered into molecular operational taxonomic units (MOTUs) based on a 97% sequence similarity, one assumes that species within the target genus have a sequence similarity of less than 97%, but this might not be the case among recently diverged species

Summary

Introduction

Chikanda is a traditional dish that consists primarily of wild-harvested terrestrial orchid tubers and peanuts (Davenport and Ndangalasi 2001). Despite the fact that all orchids are CITES appendix II listed (2014), and their international trade is subject to specific rules and permits, an estimated 2.2–4.0 million orchid tubers are illegally exported from Tanzania to Zambia each year, and a total of 85 terrestrial orchid species are identified to be at risk of overharvesting (Davenport and Ndangalasi 2003; Veldman et al 2014). This enormous pressure on Tanzanian orchid populations is unsustainable, and Tanzanian collectors are increasingly forced to look for alternative collection sites further away (Davenport and Ndangalasi 2003; Nyomora 2005; Challe and Price 2009)

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