L limonene

Ten microliters of D-limonene (product no. 62,118, analytical standard, Sigma-Aldrich, St. Louis, MO, USA) or L-limonene (product no. 62,128, analytical standard, Sigma-Aldrich) was dissolved in 10 mL ethanol (95%) as a stock solution, which was used within one week. For the Y-maze olfactometer experiment, about 30–960 µL of stock solution was bought up to 10 mL with water, and then 2 mL of the solution was transferred onto a cotton ball beside the rice plants. The final concentration of limonene (1.5–48 nL/L) in the container was calculated by dividing the actual amount of limonene by the volume of the glass container (~4 L). Solvent blanks (cotton balls with an equal volume of solvent) served as controls. For the solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) analysis (see below), the stock solution was further diluted 10-fold to 1 nL/10 µL with ethanol (95%). Finally, 10–50 µL of the solution was used.

Phytochemicals such as 1-cyclohexyl-2-pyrrolidone, camphene, cinnamaldehyde, citral, geraniol, L-carvone, L-limonene, L-menthol, β-myrcene, ocimene, α-terpinene, and β-terpinene (Figure 1) and other essential chemicals were purchased from Sigma-Aldrich Chemicals Pvt. Ltd., India.