Solanum habrochaites, S. Knapp & D. M. Spooner

Wang, Fumin, Park, Yong-Lak & Gutensohn, Michael, 2020, Glandular trichome-derived sesquiterpenes of wild tomato accessions (Solanum habrochaites) affect aphid performance and feeding behavior, Phytochemistry (112532) 180, pp. 1-11 : 2

2.1. Solanum habrochaites chemotypes produce distinct sets of glandular trichome derived sesquiterpenes

To identify glandular trichome derived terpene traits in tomato that have the potential to improve the plant defense against piercing-sucking pests such as the potato aphid ( M. euphorbiae ) we have assembled and screened a collection of two S. lycopersicum cultivars and ten S. habrochaites accessions that based on previous analyses ( Gonzales-Vigil et al., 2012) represent five distinct chemotypes with specific terpene profiles. To test if the results of this previous characterization of glandular trichome derived terpenes could be verified for tomato plants grown under our conditions, we performed leaf dip extractions for these tomato accessions and analyzed the resulting extracts by combined gas chromatography-mass spectrometry (GC-MS). Indeed, our analysis confirmed that the blend of terpenes produced in glandular trichomes differed significantly between S. lycopersicum and S. habrochaites , as well as among different S. habrochaites accessions (Table S1). The two S. lycopersicum cultivars (c.v. M82 and c.v. Moneymaker) produced a mixture of monoterpenes with β- phellandrene being the most prominent compound besides smaller amounts of α- pinene, δ-2-carene, and α- phellandrene. In addition, both cultivars produced minor amounts of the sesquiterpenes β- caryophyllene and α- humulene, while δ- elemene was only found in extracts of c.v. M82. In contrast to the S. lycopersicum cultivars the S. habrochaites accessions lack monoterpenes and can be sorted into five different chemotypes based on the profile of sesquiterpenes produced (Table S1). Chemotype 1 includes the S. habrochaites accessions LA1691 and LA2650, and primarily produces 7-epizingiberene and smaller quantities of R -curcumene. Leaf dip extracts from chemotype 2, represented by the accessions LA 1721 and LA1927, contained large amounts of γ- elemene in addition to smaller amounts of δ- elemene. A similar qualitative composition was found for extracts from chemotype 3, including accessions LA1978 and LA2155; however, these contained large amounts of δ- elemene and only small quantities of γ- elemene. Extracts from chemotype 4, represented by accessions LA1775 and LA1779, also contained large amounts of γ- elemene and small amounts of δ- elemene like those from chemotype 2. However, accessions of chemotype 4 are characterized by the production of substantial amounts of α- santalene, α- bergamotene and β- bergamotene as well as a few minor compounds including β- elemene and (Z)-α- farnesene. Extracts from chemotype 5, comprised of accessions LA 1624 and LA2860, contained the two sesquiterpenes β- caryophyllene and α- humulene that were also found in S. lycopersicum , however, at up to 26- and 51-fold higher quantities, respectively. While δ- elemene, γ- elemene, and β- elemene were found in the extracts of many accessions, including those of chemotypes 2, 3, 4, and c.v. M82, these are likely the result of Cope rearrangements occurring upon sample injection into the hot (220 ◦ C) GC injector port ( Colby et al., 1998), thus suggesting that glandular trichomes of these accessions produce germacrene C, B, and A, respectively.

The analysis of tomato leaf dip extracts revealed the accumulation of terpenes in glandular trichomes, which can affect aphids once they are on the leaf surface. However, the behavior of aphids could already be modified prior to landing on the host plant through terpenes emitted from leaves into the atmosphere. Thus, we also performed headspace collections from leaves followed by GC-MS analysis to characterize the profile of emitted terpenes for all the tomato accessions qualitatively and quantitatively. In summary the results of this analysis of emitted terpenes (Table S2) are in line with the previous analysis of leaf dip extracts and further confirm the observed differences in the terpene profiles between S. lycopersicum and the five S. habrochaites chemotypes .