South African Journal of Botany 96 (2015) 78–84 Contents lists available at ScienceDirect South African Journal of Botany journal homepage: www.elsevier.com/locate/sajb Chemical variations, trichome structure and antifungal activities of essential oils of Helichrysum splendidum from South Africa M. Mashigo a,⁎,S.Combrincka,T.Regnierb,W.DuPlooyc,W.Augustyna,N.Mokgalakaa a Department of Chemistry, Tshwane University of Technology, PO Box 56208, Arcadia, Pretoria 0001, South Africa b Department of Biotechnology and Food Technology, Tshwane University of Technology, PO Box 56208, Arcadia, Pretoria 0001, South Africa c 25 Kaptein Jan Street, Rietondale 0084, South Africa article info abstract Article history: The chemical profiles of essential oils isolated from nine populations of Helichrysum splendidum were obtained by Received 23 June 2014 gas chromatography. Plants were harvested in both summer and winter seasons in two provinces of South Africa. Received in revised form 15 October 2014 Essential oils originating from Limpopo Province were characterized by high levels of β-phellandrene, 1,8-cineole, Accepted 24 October 2014 δ-cadinene, α-cadinol, τ-cadinol, and β-pinene. These could be clearly distinguished through multivariate analysis Available online xxxx from those collected in Mpumalanga Province. The Mpumalanga oils contained germacrene D, spathulenol and bicyclogermacrene as major constituents. Seasonal variations in the volatile compositions and yields were observed. Keywords: Helichrysum splendidum A prediction model obtained through orthogonal projection to latent structures discriminant analysis was used to Essential oils compare the essential oil profiles to that of a commercial H. splendidum sample, in addition to those reported for Trichomes Zimbabwean specimens. One of the specimens from Zimbabwe differed substantially from all the others, indicating Chemometric analysis the existence of more chemotypes. The structures of the oil-bearing trichomes, as observed on the leaf surfaces Fruit decay pathogens using scanning electron microscopy, were investigated and are described for the first time. Since this investigation forms part of an ongoing screening of plants to identify natural alternatives to synthetic fungicides, the essential oils were tested in vitro against several economically important pathogens of fruit. Essential oils from Mpumalanga specimens totally inhibited the growth of Alternaria alternata from avocado and Colletotrichum gloeosporioides isolated from mango at a concentration of 500 μL/L in a toxic medium assay. The presence of high concentrations of germacrene D, spathulenol and bicyclogermacrene probably contributed to the antifungal properties of these essential oils. © 2014 SAAB. Published by Elsevier B.V. All rights reserved. 1. Introduction (Chagonda et al., 1999; Marongiu et al., 2006)havereportedonthe constituents of EOs from H. splendidum growing in Zimbabwe. The genus Helichrysum (Asteraceae) comprises about 600 species Chagonda et al. (1999) identified α-pinene, β-pinene, α-phellandrene, worldwide, with almost 250 species distributed throughout South α-terpinene, 1,8-cineole, bicyclogermacrene, δ-cadinene and cubebol as Africa (Hillard, 1983). Helichrysum splendidum (Thunb.) Less., a perenni- major constituents of the hydrodistillate. More recently, Marongiu et al. al shrub, occurs throughout South Africa, as well as in Swaziland, (2006) reported high concentrations of δ-cardinene and α-cadinol Lesotho and Zimbabwe (Chagonda et al., 1999; Germishuizen et al., in the EO, together with β-phellandrene, α-cadinol, germacrene D, 2006). The plant is used as a fuel source and for the treatment of various δ-cardinene, bicyclogermacrene, γ-cadinene and α-muurolol. These conditions associated with rheumatism (Pooley, 2003). In Zimbabwe, reports confirm the existence of different profiles for the same the Shona people use the plant to combat colds, flu and pneumonia, Helichrysum species from different localities. Variation in EO composi- and as a general antiseptic (Chagonda et al., 1999). Volatile compounds tion has been reported for a related species, Helichrysum cymosum released from boiling the leaves are inhaled to promote sweating (Bougatsos et al., 2004; Van Vuuren et al., 2006), but no comparative (Tramed Database, Index card 547 as cited by Swanepoel, 1997). The studies on the chemotypic variations of EOs from H. splendidum have plant has a pleasant fragrance, explaining its popularity as a perfume been described. In this study, EOs were obtained in summer and winter amongst rural communities (Dlamini, 1981). from nine populations growing in two provinces of South Africa and Since the chemical composition of an essential oil (EO) is inextricably analysed by gas chromatography (GC)-mass spectrometry (MS) and linked to its pharmacological properties, it is vital that the composition is GC-flame ionization detection (FID). Chemometric models were con- known prior to the development of antimicrobial agents. Two studies structed from the data to establish trends and clustering patterns within the dataset. ⁎ Corresponding author. Tel.: +27 12 382 6396. Volatile organic compounds are produced and stored in glandular E-mail address: [email protected] (M. Mashigo). trichomes, which can be used as reliable taxonomic characters for the http://dx.doi.org/10.1016/j.sajb.2014.10.006 0254-6299/© 2014 SAAB. Published by Elsevier B.V. All rights reserved. M. Mashigo et al. / South African Journal of Botany 96 (2015) 78–84 79 identification of species and for resolving taxonomic conflicts (Hayat ionization detector (FID) and a mass spectrometer (Model 5973). et al., 2009). Histochemical studies of surface appendages shed light Using an autosampler, a 1.0 μL sample volume was introduced into on the location and type of secondary metabolites produced by the the inlet, maintained at 250 °C, and split according to a 1:200 ratio. plant (Afolayan and Meyer, 1995). Although the glandular trichomes Separation was achieved on an HP-Innowax polyethylene glycol of a few Helichrysum species have been described (Afolayan and column (60 m × 250 μmi.d.;0.25μm film thickness). The oven temper- Meyer, 1995; Ascensão et al., 2001; Mathekga, 2001), such reports are ature was held at 60 °C for the initial 10 min, then increased to 220 °C at sparse, considering the size of the genus Helichrysum worldwide. To a rate of 4 °C/min and held for 10 min, before increasing to 240 °C at a contribute to the available knowledge, a preliminary investigation of rate of 4 °C/min. Helium was used as carrier gas at a constant flow the glandular structures of H. splendidum was conducted using scanning rate of 1.2 mL/min. The FID was maintained at 250 °C. Mass spectra electron microscopy. were obtained, after ionization in electron impact mode at 70 eV, over Effective natural mycobiocides are needed to protect the supply the scanning range m/z 35 to 550. A transfer line temperature of 280 °C chains of fresh products against fungal decay, while minimizing envi- was maintained. The relative percentage peak areas of the individual ronmental problems by eliminating synthetic fungicides (Du Plooy components were obtained from the FID data, while the MS data were et al., 2009). High costs associated with the removal of hazardous used for identification. Compound identities were verified by comparing chemical waste in packhouses may result in the irresponsible disposal their retention indices and mass spectra with those of authentic stan- of fungicide residues, with detrimental effects on the environment. dards and compounds contained in the NIST®, Mass Finder® and Flavor® The fate of crop protection products in soils is associated with a series spectral libraries. of intricate processes, which sometimes result in the migration of resi- dues into ground water (Taube et al., 2002). Our research team has 2.3. Chemometric analysis of data been involved in the identification of plant extracts and particularly EOs as green alternatives to synthetic crop protection products. Data obtained from GC analyses were exported to SIMCA-P 13.0 Towards this aim, the EOs isolated in this study were evaluated for chemometrics software (Umetrics AB, Malmo, Sweden). Pareto scaling their abilities to inhibit the growth of important fungal decay pathogens was applied, but no preprocessing of the data was done. Principal compo- of fruit. nent analysis (PCA) models were constructed from individual and com- bined datasets and the resulting scores plots were visually inspected to 2. Materials and methods determine the presence of possible outliers. Orthogonal projections to latent structures discriminant analysis (OPLS-DA) were applied to distin- 2.1. Collection of plant material and isolation of essential oils guish the populations from the two provinces, as well as the EOs obtained from specimens harvested in different seasons. Loading plots generated Aerial parts, including flowers, of H. splendidum (Genspec nos: from the model statistics indicated constituents contributing significantly 3240-397A to I) were collected in the Limpopo and Mpumalanga to the differences observed between the EOs obtained from the various provinces of South Africa in summer (November 2010). Five specimens populations. Results from the analysis of the commercial oil and results were harvested from each of nine populations (Table 1). Herbarium published by Chagonda et al. (1999) and Marongiu et al. (2006) were in- specimens were prepared and identified by staff of the South African corporated into the data