2 3 butanediol isomers

The following compounds were used as authentic standards in the GC-MS and GC-FID assays. Ethyl propanoate (99% purity), 2,3-butanediol isomers (98%), ethyl 2-methylpropanoate (≥ 98%), ethyl 2-methylbutanoate (≥ 98%), n-propyl 2-methylpropanoate (≥ 97%), 4-heptanone (98%), 2-ethyl-1-hexanol (≥ 99.6%), diethyl succinate (99%), 2-bornanone (≥ 97%), methyl dodecanoate (≥ 98%), ethyl dodecanoate (≥ 98%), methyl tetradecanoate (≥ 98%), ethyl tetradecanoate (99%), ethyl (Z)-9-tetradecenoate (97%), ethyl hexadecanoate (≥ 99%), ethyl (Z)-9-octadecenoate (98%) and n-hexane (≥ 97%) were procured from Sigma-Aldrich (St. Louis, MO, USA). Ethyl (Z)-9-hexadecenoate and ethyl (E)-9-octadecenoate, N-(2-methylbutyl)acetamide, N-(3-methylbutyl)acetamide, N-(2-methylbutyl)propanamide, N-(3-methylbutyl)propanamide, N-(2-methylbutyl)-2-methylpropanamide and N-(3-methylbutyl)-2-methylpropanamide, all at ≥ 98.0% purity (by GC), were synthesised previously [53 (link), 55 (link)].

The field trial was conducted in Geumsan-gun, Chungcheongnam-do, South Korea (36°35′ 32.27′′North, 127°30′ 34.75′′East), where plants are affected by multiple viral diseases each year, in mid-April of 2016 and 2017. For the field study, all necessary permits were obtained from the owners of private lands. Pepper seedlings (Capsicum annum L. cv. Bukwang) were transplanted at a distance of 30 cm. Before transplanting, the furrows were covered with black polyethylene plastic film to prevent weed problems. To test induced resistance under field conditions, 1-month-old seedlings were drenched with 100 ml per plant of 1 mM 2,3-butanediol isomers (2R,3R form, 2S,3S form, and 2R,3S form) (Sigma–Aldrich Corp., Korea) and 1 mM BTH solution three times per month. The same volume of sterilized water was used as a negative control. Each treatment was replicated five times in a completely randomized block design and consisted of 20 plants per treatment.