Sesquiterpene lactone composition of wild and cultivated sunflowers and biological activity against an insect pest

Authors: Prasifka, Jarrad; SPRING, OTMAR - University Of Hohenheim; CONRAD, JURGEN - University Of Hohenheim; Cook, Leonard; Palmquist, Debra; Foley, Michael

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2015
Publication Date: 4/29/2015
Citation: Prasifka, J.R., Spring, O., Conrad, J., Cook, L.W., Palmquist, D.E., Foley, M.E. 2015. Sesquiterpene lactone composition of wild and cultivated sunflowers and biological activity against an insect pest. Journal of Agricultural and Food Chemistry. 63(16):4042-4049. doi:10.1021/acx.jafc.5b00362.

Interpretive Summary: Chemicals known as sesquiterpene lactones (STL) are important to sunflowers’ interactions with pathogens, weeds and insects. Across 60 different sunflowers grown under field conditions, differences in composition of STL extracted from florets were found between wild and cultivated sunflowers, but also between distinct groups of inbreds used to produce commercial hybrids. Relative amounts of STL were influenced by the number of glandular trichomes (= hairs) per floret, but even after accounting for the effect of trichome number, strong correlations remained between one compound, argophyllone B, and three other compounds. Statistical analysis indicated the presence and abundance of argophyllone B, niveusin B, and 15-hydroxy-3-dehydrodesoxyfruticin were usually effective at classifying wild sunflowers, cultivated inbreds and hybrids. However, there were entries that would be grouped incorrectly (e.g., wild sunflowers which resembled inbred maintainers) based solely on STL content. In laboratory tests, argophyllone B reduced the mass of sunflower moth larvae by over 30%, but only at a very high dose. Lower doses of mixed extracts from cultivated sunflower florets produced a similar (about 40%) reduction in larval mass after 7 days, suggesting multiple STL act together. Though results support the idea that STL are valuable for defense against some sunflower insects, more information is needed to use these compounds purposefully in breeding.

Technical Abstract: Sesquiterpene lactones in sunflowers, Helianthus spp., are important to interactions with pathogens, weeds and insects. Across a broad range of H. annuus, differences in composition of sesquiterpene lactones extracted from florets were found between wild and cultivated sunflowers, but also between distinct groups of inbreds (heterotic groups) used to produce sunflower hybrids. Relative amounts of sesquiterpene lactones were correlated with the estimated density of glandular trichomes per floret, but strong (r > 0.70) partial correlations remained between argophyllone B and three other compounds. Discriminant function analysis showed the presence and relative abundance of argophyllone B, niveusin B, and 15-hydroxy-3-dehydrodesoxyfruticin were usually (75%) effective at classifying wild sunflowers, cultivated inbreds and hybrids. However, there were entries that would be grouped incorrectly (e.g., wild sunflowers which resembled inbred maintainers) based solely on composition of sesquiterpene lactones. In bioassays with larvae of the sunflower moth, Homoeosoma electellum, argophyllone B reduced sunflower moth larval mass by >30%, but only at a dose greater than that found in wild or cultivated florets. Relatively low doses of mixed extracts from cultivated sunflower florets produced a similar (˜40%) reduction in larval mass after 7 d, suggesting that combinations of sesquiterpene lactones act additively. Though results support a role of sesquiterpene lactones in herbivore defense for cultivated sunflowers, additional information on the relative effects and basis for quantitative differences of sesquiterpene lactones is needed to use these compounds purposefully in breeding.