Secondary metabolites of the leaf surface affected by sulphur fertilisation and perceived by the diamondback moth

Abstract

Summary. Oilseed rape, Brassica napus L. (cv Express), plants were grown under three different sulphur regimes: sulphur-free (S 0 ), normal sulphur (S n , normal field concentration) and a sulphur-rich (S + , 2 × concentration of S n ). We performed dual choice oviposition assays with the diamondback moth, Plutella xylostella, using real plants and, for the first time with this insect, artificial leaves sprayed with methanolic leaf-surface extracts. The results mirrored those of a separate study of preferences for whole plants. Females laid more eggs on surrogate leaves that were treated with S n extracts than on S 0 plants, while only a slight, not significant, difference was observed between extracts of normal and sulphur-rich plants. This shows that chemical compounds on the leaf surface mediate the oviposition preference and that the female insect can perceive the quality of the host-plants in terms of their fertilisation status.Since leaf volatiles are known to be oviposition stimulants, we investigated the effects of leaf-surface extracts on insect olfactory responses using electroantennograms (EAGs). In agreement with the behavioural data, we found that extracts of sulphur-treated plants yielded higher EAG amplitudes than the S 0 extracts. Since the leaf content of the volatiles isothiocyanates is influenced by sulphur nutrition, we analysed the extracts for these compounds. Above the detection threshold of our GC-MS system, no isothiocyanates were found. Thus, other compounds present in the surface extracts must be perceived by the antenna.However, the HPLC analysis revealed 11 different glucosinolates. Progoitrin (2-Hydroxy-3-butenyl) and gluconapoleiferin (2-Hydroxy-4-pentenyl), which belong to the hydroxy-alkene class of glucosinolates, were the most abundant compounds. The total glucosinolate content sharply increased from S 0 to S n plants, whereas it was slightly lower in S n versus S + plants. Since it is known that glucosinolates can stimulate oviposition, it seems likely that the increased content we observed was influencing the insect preference in this study too.

Defence mechanisms of Brassicaceae: implications for plant-insect interactions and potential for integrated pest management. A review

“…Furthermore, surrogate leaves treated with methanolic leaf surface extracts of B. napus plants that received three different sulphur fertilisation treatments showed even more marked differences by the oviposition choice of cabbage root fly than the potted plants. The oviposition data was shown to be positively correlated either with CIF or glucosinolates (Marazzi et al, 2004a). Investigation on application of eleven cruciferspecific phytoalexins and related synthetic compounds on surrogate paper leaves, being offered to cabbage root flies in oviposition assays, showed three of them (methoxybrassinin, cyclobrassinin and brassicin) to be significantly stimulatory, whereas the remaining metabolites had no effect, suggesting that the reaction of the fly appears to be structure-specific (Baur et al, 1998).…”

“…Apart from glucosinolates, Brassica phytoalexins have been documented as playing a significant role in oviposition (Roessingh et al, 1997;Baur et al, 1996Baur et al, , 1998De Jong et al, 2000;Hurter et al, 1999;Marazzi et al, 2004a, b). Two compounds, the so-called "Cabbage Identification Factors" (CIFs) are isolated from the surface of B. oleracea cv.…”

“…alba and B. nigra) and demonstrated that the constituents of host plants affected larval feeding and oviposition of P. xylostella. In order to observe sulphur perception by the diamondback moth, Marazzi et al (2004a) raised B. napus plants under three different sulphur regimes: sulphur-free, normal field concentration and sulphur-rich (twice the normal field concentration). In addition, they performed dual oviposition assays with the diamondback moth, using either Brassica plants or artificial leaves sprayed with methanolic leaf-surface extracts.…”

Consumo foliar da traça-das-crucíferas em couve e brócolis tratados com sinigrina

“…: Plutellidae), é uma praga especialista encontrada em mais de 40 espécies de brássicas, causando danos e reduzindo significativamente a produção em diversas regiões do mundo (Marazzi et al, 2004;Cheng et al, 2008).…”

“…Os glicosinolatos são um grupo de químicos secundários de plantas característicos na família Brassicaceae (Reichelt et al, 2002;Marazzi et al, 2004;Barker et al, 2006;Cartea et al, 2011), que podem reduzir o ataque de insetos herbívoros (Van Poecke et al, 2003;Renwick et al, 2006). A sinigrina (2-propenylglucosinolate) pertence ao grupo dos glicosinolatos e ocorre naturalmente em plantas de brássicas, possuindo também propriedades anticarcinogênicas (Shelton;Nault, 2004;Halkier;Gershenzon, 2006;Martin;Müller, 2007;Velasco et al, 2007;Kehr;Buhtz, 2011;Peres, 2013).…”