## 2 Materials and Methods
### Analysis of Volatile Compounds from Aphid-Infested, Endophytically-Colonized Leaves  
Treated and control plants were produced as described previously. Five adult aphids were retained in clip cages on one sprayed and one unsprayed leaf from each replicate treated and control plant and incubated for 6 days at 25 \(\pm\) 2 \({}^{\circ}\)C, 16:8 h lightdark regime, and 70% RH. There were 18 replicate treated  
Figure 1: Design of an experimental arena for the choice bioassay. The set-up consists of one large Petri dish (150 mm \(\times\) 15 mm) with two holes (diameter 25 mm each) in the bottom and covered by the lid. The area in contact with the plant was lined with eva rubber to avoid damaging the leaves. Aphids could choose between an unsprayed but endophytically-colonized leaf and a leaf from the control plant, or they could remain in the neutral area (no choice). The final position (endophytically-colonized leaf, control leaf, or neutral area) was recorded.  
plants per isolate and 18 control plants. After 6 days, the leaves on which the aphids had been feeding were sampled and the volatiles evaluated. Homogenates of each leaf were prepared according to [PERSON] et al. [28]. Briefly, 3 g from each leaf was homogenized for 1 min at 19,500 rpm in 6 mL of distilled water using an A 11 IKA analysis mill (IKA, Werke GmbH & Co.KG, Staufen, Germany). The sample was allowed to equilibrate for 5 min at 25 \({}^{\circ}\)C; 1 mL aliquots of homogenate were placed in vials containing the same volume of a saturated CaCl\({}_{2}\) solution, sealed and stored at \(-20\) \({}^{\circ}\)C prior to analysis.  
Volatile compounds were extracted from the samples using solid-phase microextraction (SPME) and analyzed using a High-Resolution Gas Chromatograph with Triple Quadrupole systems Mass Spectrometry (HR-GC-TQ MS) (Bruker model Scion 456-GC-TQ MS system; Bruker, MA, USA). Method parameters were set based on previous work [28]. Briefly, each sample was heated to 40 \({}^{\circ}\)C and allowed to equilibrate for 10 min; a preconditioned SPME fiber (50/30 \(\upmu\)m DVB/CAR/PDMS Stableflex 23 Ga, Autosampler, SUPELCO, Bellefonte, PA, USA) was then introduced into the vial and volatile compounds were adsorbed for 50 min. Desorption of volatile compounds was done directly into the GC injector at 250 \({}^{\circ}\)C for 5 min. A Supelcowax 10 capillary column (30 m \(\times\) 0.25 mm, 0.25 \(\upmu\)m, Sigma-Aldrich Co. LLC, St. Louis, MO, USA) was used with the following parameters: Helium as the carrier gas; injector and detector set at 250 \({}^{\circ}\)C; column held for 5 min at 40 \({}^{\circ}\)C and then the temperature programed to increase at a rate of 4 \({}^{\circ}\)C min\({}^{-1}\) until it reached 200 \({}^{\circ}\)C.  
Identification of the volatile compounds detected was done by comparing their retention times against available standards purchased from Sigma-Aldrich-Merck, matching them to the NIST Library, or by comparing their MS spectra with reference spectra from different libraries (resemblance percentage above 80%). The method used for the identification was as follows: EI mode (70 eV), ion source and transfer line temperatures were all fixed at 250 \({}^{\circ}\)C. Mass spectra were obtained in full scan mode in the 300 to 400 mass-to-charge ratio range at a scanning speed of 7 scan/s. Chromatograms and spectra were recorded and processed using the Bruker MS Workstation version 8.2 (Bruker, Billerica, MA, USA). Volatile compounds were organized according to their chemical structure with respect to aldehydes, alcohols, ketones, terpenoid and phenolic derivatives and they were semi-quantified using an external standard calibration for each chemical group using hexanal, 1-octen-3-ol, 6-methyl-5-hepten-2-one, farnesene and ethylbenzene as standards, respectively. Each compound was semi-quantified against the external standard calibration of the corresponding chemical group in mg/L of homogenate and analyzed three times in duplicate experiments.