Antimicrobial Terpenes Suppressed the Infection Process of Phytophthora in Fennel-Pepper Intercropping System

Yuxin Yang; Ying Li; Xinyue Mei; Min Yang; Huichuan Huang; Fei Du; Jiaqing Wu; Yiyi He; Junwei Sun; Haining Wang; Xiahong He; Shusheng Zhu; Yingbin Li; Yixiang Liu

doi:10.3389/fpls.2022.890534

Antimicrobial Terpenes Suppressed the Infection Process of Phytophthora in Fennel-Pepper Intercropping System

Front Plant Sci. 2022 Jun 9:13:890534. doi: 10.3389/fpls.2022.890534. eCollection 2022.

Authors

Yuxin Yang^{1

2}, Ying Li^{1

2}, Xinyue Mei^{1

2

3}, Min Yang^{1

2

3}, Huichuan Huang^{1

2

3}, Fei Du^{1

2

3}, Jiaqing Wu^{1

2}, Yiyi He^{1

2}, Junwei Sun^{1

2}, Haining Wang^{1

2

3}, Xiahong He^{1

2

3}, Shusheng Zhu^{1

2

3}, Yingbin Li^{1

2

3}, Yixiang Liu^{1

2

3}

Affiliations

¹ State Key Laboratory for Conservation and Utilization of Bio-Resources in Yunnan, Yunnan Agricultural University, Kunming, China.
² Key Laboratory for Agro-Biodiversity and Pest Control of Ministry of Education, College of Plant Protection, Yunnan Agricultural University, Kunming, China.
³ China France Plantomix Joint Laboratory, Yunnan Agricultural University, Kunming, China.

Abstract

The interactions between non-host roots and pathogens may be key to the inhibition of soilborne pathogens in intercropping systems. Fennel (Foeniculum vulgare) can be intercropped with a wide range of other plants to inhibit soilborne pathogens in biodiversity cultivation. However, the key compounds of fennel root exudates involved in the interactions between fennel roots and pathogens are still unknown. Here, a greenhouse experiment confirmed that intercropping with fennel suppressed pepper (Capsicum annuum) blight disease caused by Phytophthora capsici. Experimentally, the roots and root exudates of fennel can effectively interfere with the infection process of P. capsici at rhizosphere soil concentrations by attracting zoospores and inhibiting the motility of the zoospores and germination of the cystospores. Five terpene compounds (D-limonene, estragole, anethole, gamma-terpenes, and beta-myrcene) that were identified in the fennel rhizosphere soil and root exudates were found to interfere with P. capsica infection. D-limonene was associated with positive chemotaxis with zoospores, and a mixture of the five terpene compounds showed a strong synergistic effect on the infection process of P. capsici, especially for zoospore rupture. Furthermore, the five terpene compounds can induce the accumulation of reactive oxygen species (ROS), especially anethole, in hyphae. ROS accumulation may be one of the antimicrobial mechanisms of terpene compounds. Above all, we proposed that terpene compounds secreted from fennel root play a key role in Phytophthora disease suppression in this intercropping system.

Keywords: Phytophthora capsici; intercropping; reactive oxygen species; synergistic antimicrobial ability; terpene compounds.