Abstract
Agave saponins are a valuable resource for the prospective development of new forms of agrochemicals. The extraction method was optimized and applied to 17 Agave species. Thirteen saponin fractions (SFs) were assayed on wheat etiolated coleoptiles, and analysed using UPLC-QTOF-MSE, NMR spectroscopy and the HMBC method for aglycone identification (HMAI). Six SFs were assayed on standard target species (STS) and weeds. The new extraction method reduces costs to obtain SFs with the same activity. The tested SFs assayed on etiolated wheat coleoptiles that belong to the subgenus Agave were among those with the highest activity levels. The combination of HMAI together with UPLC-MS allowed the identification of 20 aglycones in the SFs, and no isolation or hydrolysis of the saponins was required. A Principal Component Analysis (PCA) showed that for the active SFs the structural key would be the length of their sugar chain. The presence of a carbonyl group at C-12 implied an enhancement in phytotoxic activity. Six SFs were assayed on seeds, and no activity on Solanum lycopersicum (tomato) was observed; however, good activity profiles were obtained on weed E. crus-galli (IC50 < 80 ppm), better than the commercial herbicide Logran®. These findings represent a possible lead for the development of natural herbicides through the use of saponins of subgenus Agave species.
Highlights
Plants, because of their lack of mobility and their exposure to biotic and abiotic factors, have developed the most sophisticated chemical communication systems through the production of allelochemicals [1]. synthetic herbicides may control weeds in an effective way, can they lead to an enhancement in herbicide-resistant weed populations, but they can present several detrimental effects on the environment and on human health
In order to optimize such an extraction method, leaves from A. americana were used as the starting material, since the saponin content described [25,26] for this species includes structural characteristics that suggest that its saponin fractions (SFs) would exhibit phytotoxic activity
The extract that is normally obtained contains a large amount of sugars in addition to the saponins, so this is followed by a liquid–liquid extraction with n-butanol and water to produce what is known as “crude saponins extract”
Summary
Because of their lack of mobility and their exposure to biotic and abiotic factors, have developed the most sophisticated chemical communication systems through the production of allelochemicals [1]. synthetic herbicides may control weeds in an effective way, can they lead to an enhancement in herbicide-resistant weed populations, but they can present several detrimental effects on the environment and on human health. It has been estimated that without weed control, crop yield losses might scale up to 70% [2,3] For these reasons, research works on novel, sustainable, effective and more environmentally friendly alternatives for weed management has experienced a considerable increment in the last few years. Research works on novel, sustainable, effective and more environmentally friendly alternatives for weed management has experienced a considerable increment in the last few years In this respect, saponins are some of the products that can be found in nature with a noteworthy chemical composition and biological function [4]. The chemical structure of saponins consists of a hydrophobic backbone (sapogenin or aglycone) and a hydrophilic carbohydrate chain formed by monosaccharide units linked by a glycosidic bond (Figure 1). Antifungal, insecticidal and antifeeding properties, allowing them to act as a chemical barrier against potential pathogens [4] and, they represent a valuable resource for the prospective development of new forms of agrochemicals
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