Abstract
Allelochemicals that are present in trichome secretions of wild tomato species play a major role in mediating interactions with arthropods, often conferring a high level of resistance via antibiosis and antixenosis. Many accessions of the wild tomato relative, Solanum habrochaites (S.h), possess high levels of resistance to arthropods. The monocyclic sesquiterpene hydrocarbon, 7-epi-zingiberene, is a major defensive component found in trichome secretions of certain accessions of S.h. We have used LA2329, an S.h. accession, as a donor in a breeding program designed to introgress zingiberene into cultivated tomato. However, the composition of trichome secretions in our population of LA2329 is segregating, with some individuals producing mainly 7-epi-zingiberene in their secretions while others producing two additional, unidentified compounds in their trichome secretions. To investigate if these other compounds may also contribute to arthropod resistance, trichome secretions were collected from plants of S.h LA2329 grown under greenhouse conditions and then major compounds were isolated by silica gel column chromatography and tested for their ability to repel two spotted-spider mite (TSSM), Tetranychus urticae. Isolation and identification of allelochemicals were aided by use of gas chromatography/mass spectroscopy. The results revealed the presence of three predominate chromatographic peaks: 7-epi-zingiberene, 9-hydroxy zingiberene, and 9-hydroxy,10,11-epoxy-zingiberene. Results of testing isolated compounds for repellency to TSSM using bridge bioassays revealed that the repellent activities of 9-hydroxy zingiberene and 9-hydroxy,10,11-epoxy-zingiberene were each significantly higher than that for 7-epi-zingiberene. These results support the idea that the degree of repellency may differ among plant allelochemicals and also emphasize the potential value of introgressing the presence of 9-hydroxy zingiberene and 9-hydroxy,10,11-epoxy-zingiberene into cultivated tomato to enhance its arthropod resistance.
Highlights
The tomato, Solanum lycopersicum, is one of the most widely grown and important vegetables produced worldwide (Dorais et al, 2008)
In contrast there was only one major component in washes of LA2329, chemotype B (LA2329-B) (Figure 1). The presence of this qualitative difference in trichome secretion composition between the two chemotypes supports the idea that the synthesis of secondary metabolites is very different in the two chemotypes
The Gas Chromatography - Flame Ionization Detector (GC-FID) tracings for trichome secretions from LA2167 and PI127826 demonstrated the presence of three compounds each having a retention time that was identical to one of the three components present in LA2329A
Summary
The tomato, Solanum lycopersicum, is one of the most widely grown and important vegetables produced worldwide (Dorais et al, 2008). Numerous factors can affect tomato productivity dramatically. One of these factors is arthropod infestation, resulting in direct damage and/or disease transmission (Nault and Speese III, 2002). Most cultivated tomatoes are susceptible to diseases and pests, leading growers to apply pesticides and insecticides (Letourneau and Goldstein, 2001) to control these problems. Tomato has been greatly improved by introgression of disease resistance genes from wild relatives (Hajjar and Hodgkin, 2007; Firdaus et al, 2012). There are wild tomato accessions that are highly resistant to a wide range of arthropod pests (Freitas et al, 2002), but introgression of arthropod resistance into commercially accepted tomato varieties remains an unfulfilled goal
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