**Fan Yang** †**, Xiaoxue Liu** †**, Hui Wang, Rui Deng, Hanhan Yu and Zhihui Cheng \***

College of Horticulture, Northwest A&F University, Taicheng Road No.3, Yangling, Shaanxi 712100, China

**\*** Correspondence: chengzh@nwsuaf.edu.cn; Tel.: +86-151-2918-3300

† These authors contributed equally to the article.

Academic Editor: Igor Jerkovi´c Received: 13 August 2019; Accepted: 5 September 2019; Published: 7 September 2019

**Abstract:** Garlic and formulations containing allicin are used widely as fungicides in modern agriculture. However, limited reports are available on the allelopathic mechanism of green garlic volatile organic compounds (VOCs) and its component allelochemicals. The aim of this study was to investigate VOCs of green garlic and their effect on scavenging of reactive oxygen species (ROS) in cucumber. In this study, green garlic VOCs were collected by HS-SPME, then analyzed by GS-MS. Their biological activity were verified by bioassays. The results showed that diallyl disulfide (DADS) is the main allelochemical of green garlic VOCs and the DADS content released from green garlic is approximately 0.08 mg/g. On this basis, the allelopathic effects of green garlic VOCs in vivo and 1 mmol/L DADS on scavenging of ROS in cucumber seedlings were further studied. Green garlic VOCs and DADS both reduce superoxide anion and increase the accumulation of hydrogen peroxide of cucumber seedlings. They can also regulate active antioxidant enzymes (SOD, CAT, POD), antioxidant substances (MDA, GSH and ASA) and genes (*CscAPX*, *CsGPX*, *CsMDAR*, *CsSOD*, *CsCAT*, *CsPOD*) responding to oxidative stress in cucumber seedlings.

**Keywords:** green garlic volatile organic compounds; volatiles isolation and analysis; allelochemicals; GC-MS; biological activity; reactive oxygen species
