Abstract
Acylsugars are secondary metabolites exuded from type IV glandular trichomes that provide broad-spectrum insect suppression for Solanum pennellii Correll, a wild relative of cultivated tomato. Acylsugars produced by different S. pennellii accessions vary by sugar moieties (glucose or sucrose) and fatty acid side chains (lengths and branching patterns). Our objective was to determine which acylsugar compositions more effectively suppressed oviposition of the whitefly Bemisia tabaci (Gennadius) (Middle East—Asia Minor 1 Group), tobacco thrips, Frankliniella fusca (Hinds), and western flower thrips, Frankliniella occidentalis (Pergande). We extracted and characterized acylsugars from four S. pennellii accessions with different compositions, as well as from an acylsugar-producing tomato breeding line. We also fractionated the acylsugars of one S. pennellii accession to examine the effects of its components. Effects of acylsugars on oviposition were evaluated by administering a range of doses to oviposition sites of adult whiteflies and thrips in non-choice and choice bioassays, respectively. The acylsugars from S. pennellii accessions and the tomato breeding line demonstrated differential functionality in their ability to alter the distribution of whitefly oviposition and suppress oviposition on acylsugar treated substrates. Tobacco thrips were sensitive to all compositions while western flower thrips and whiteflies were more sensitive to acylsugars from a subset of S. pennellii accessions. It follows that acylsugars could thus mediate plant-enemy interactions in such a way as to affect evolution of host specialization, resistance specificity, and potentially host differentiation or local adaptation. The acylsugars from S. pennellii LA1376 were separated by polarity into two fractions that differed sharply for their sugar moieties and fatty acid side chains. These fractions had different efficacies, with neither having activity approaching that of the original exudate. When these two fractions were recombined, the effect on both whiteflies and thrips exceeded the sum of the two fractions’ effects, and was similar to that of the original exudate. These results suggest that increasing diversity of components within a mixture may increase suppression through synergistic interactions. This study demonstrates the potential for composition-specific deployment of acylsugars for herbivore oviposition suppression, either through in planta production by tomato lines, or as biocides applied by a foliar spray.
Highlights
Plants produce an enormous diversity of secondary metabolites with specialized functions [1,2]
Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) Middle East—Asia Minor 1 Group (MEAM1), causes direct damage to tomato through its saliva’s toxic effects and plant debilitation from sap removal [10]and indirectly as it is the vector of tomato yellow leaf curl virus, which is capable of causing severe stunting, reduced leaf size, chlorosis, and premature flower drop
Seeds from S. pennellii accessions LA1732, LA1376, and LA2560 were obtained from the Tomato Genetics Resource Center (TGRC) at the University of California at Davis
Summary
Plants produce an enormous diversity of secondary metabolites with specialized functions [1,2] These compounds exist in a wide range of classes with vast numbers of smaller modifications and serve vital roles in plant-environment interactions, in plant defense where they can act as antagonists to insect herbivores [3]. Levels of defensive secondary metabolites are thought to have been reduced as a result of domestication in several important crop species [4,5,6] One such plant is the cultivated tomato [7], Solanum lycopersicum, a vegetable of world-wide economic importance, thought to have been domesticated from its weedy relative S. lycopersicum var cerasiforme [8]. Breeding defensive secondary metabolic production into cultivated tomato may supplement current defenses, and provide a durable means of controlling insect-mediated damage to plants
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