Effects of saponin-rich quinoa (Chenopodium quinoa Willd.) bran and bran extract in diets of adapted and non-adapted quinoa pests in laboratory bioassays

Nathaniel B Mccartney,Angélica M Fierro,M Isabel Ahumada,Rodrigo A Chorbadjian,Marcela Muñoz,Marlene Rosales

doi:10.7764/rcia.v46i2.2159

Nathaniel B Mccartney, Angélica M Fierro + Show 4 more

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https://doi.org/10.7764/rcia.v46i2.2159

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Abstract

Quinoa ( Chenopodium quinoa Willd.) produces bitter-tasting triterpene saponins that must be removed prior to consumption, significantly adding to production costs. Breeders have therefore prioritized the development of low-saponin “sweet” cultivars with little concern for the ecological benefits these compounds may confer. Quinoa saponins are thought to provide protection against herbivores and microbial pathogens, although there is very little data to support these assumptions. Here we begin to address the question of whether biologically relevant concentrations of saponins exert negative effects against insects and pathogens that attack quinoa, as well as against species not associated with quinoa. Using bran of the coastal genotype Cahuil as the source of saponins, we conducted feeding assays with larvae of 3 noctuid insect species. Antifungal activity against 8 species was assayed using bran extract incorporated into PDA media. Quinoa bran showed insecticidal activity against only the non-quinoa feeder Pseudaletia impuncta , while the quinoa feeders T richoplusia ni and Feltia subterranea were not affected. The bran extract inhibited fungal colony growth of Alternaria arborescens , Botrytis cinerea , and Phytophthora cinnamomi by approximately 50% but had less growth inhibitory effect on Fusarium oxysporum f. sp. cepae, Pestalotiopsis clavispora , Penicillium digitatum , Geotrichum sp ., and the quinoa pathogen Phoma sp. The relatively higher inhibitory activity against some pathogen species did not necessarily correlate with their expected pathogenicity against quinoa. The results of this study suggest that, while the quinoa saponins present in bran and bran extracts may provide some protection against certain insects and phytopathogens, species-specific responses need further exploration.

Highlights

Chenopodium quinoa Willd. is a crop plant from the Amaranthaceae family that has been domesticated and widely cultivated throughout the Andean region of South America since the pre-Columbian era
Four of the seven previously described triterpene saponin aglycones were identified in the extracts of Cáhuil seeds and bran, including hederagenin, oleanolic acid, phytolaccagenic acid, and serjanic acid, with oleanolic acid being the most abundant sapogenin observed in this genotype at about 40% of the total sapogenin mass
Feeding quinoa bran to the quinoa pests F. subterranea and T. ni produced no observable negative effects on survival or developmental time, suggesting that the abundances and/or types of saponins produced by Cáhuil plants are not sufficient to provide protection against these adapted species

Summary

Introduction

Chenopodium quinoa Willd. is a crop plant from the Amaranthaceae family that has been domesticated and widely cultivated throughout the Andean region of South America since the pre-Columbian era. Mechanical dehulling may be used to debitter the seeds by abrasion of the pericarp (Reichert et al, 1986), which has the advantages of reducing water usage and producing as a byproduct a dry powder at a rate of 3 to 8% by weight (Lozano et al, 2012). This byproduct, referred to as bran or “mojuelo” (Flores et al, 2005), is increasingly utilized by industry for its saponin content, which may be between 17 and 35% (San Martin et al, 2008; Lozano et al, 2012)

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