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

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 Cáhuil 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 Trichoplusia 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.