*Review* **Research Advances in Allelopathy of Volatile Organic Compounds (VOCs) of Plants**

**Yiqi Xie 1,2, Libo Tian 2, Xu Han 1,\* and Yan Yang 1,\***

<sup>2</sup> College of Horticulture, Hainan University, Haikou 570228, China; faiy7play@163.com

**\*** Correspondence: hanxu@catas.cn (X.H.); yangyan@catas.cn (Y.Y.); Tel.: +86-186-8976-3830 (X.H.); +86-135-1803-1806 (Y.Y.)

**Abstract:** Allelopathy is an ecological phenomenon in which organisms interfere with each other. As a management strategy in agricultural systems, allelopathy can be mainly used to control weeds, resist pests, and disease and improve the interaction of soil nutrition and microorganisms. Volatile organic compounds (VOCs) are allelochemicals volatilized from plants and have been widely demonstrated to have different ecological functions. This review provides the recent advance in the allelopathic effects of VOCs on plants, such as growth, competition, dormancy, resistance of diseases and insect pests, content of reactive oxygen species (ROS), enzyme activity, respiration, and photosynthesis. VOCs also participate in plant-to-plant communication as a signaling substance. The main methods of collection and identification of VOCs are briefly summarized in this article. It also points out the disadvantages of VOCs and suggests potential directions to enhance research and solve mysteries in this emerging area. It is necessary to study the allelopathic mechanisms of plant VOCs so as to provide a theoretical basis for VOC applications. In conclusion, allelopathy of VOCs released by plants is a more economical, environmentally friendly, and effective measure to develop substantial agricultural industry by using the allelopathic effects of plant natural products.

**Keywords:** allelochemicals; VOCs properties; VOCs action; VOCs detection; green agriculture
