Volatile Signals From Guava Plants Prime Defense Signaling and Increase Jasmonate-Dependent Herbivore Resistance in Neighboring Citrus Plants.

Siquan Ling,Syed Arif Hussain Rizvi,Siwei Wang,Xinnian Zeng,Jiali Liu,Ting Xiong,Yanping Gu

doi:10.3389/fpls.2022.833562

Abstract

Intercropping can reduce agricultural pest incidence and represents an important sustainable alternative to conventional pest control methods. Citrus intercropped with guava (Psidium guajava L.) has a lower incidence of Asian citrus psyllid (ACP, Diaphorina citri Kuwayama) and huanglongbing disease (HLB), but the mechanisms are still unknown. In this study, we tested whether volatile organic compounds (VOCs) emitted by guava plants play a role in plant–plant communications and trigger defense responses in sweet orange (Citrus sinensis L. Osbeck) in the laboratory. The results showed that the behavioral preference and developmental performance of ACP on citrus plants that were exposed to guava VOCs were suppressed. The expression of defense-related pathways involved in early signaling, jasmonate (JA) biosynthesis, protease inhibitor (PI), terpenoid, phenylpropanoid, and flavonoid biosynthesis was induced in guava VOC-exposed citrus plants. Headspace analysis revealed that guava plants constitutively emit high levels of (E)-β-caryophyllene and (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), which can induce the accumulation of JA and promote stronger defense responses of citrus to ACP feeding. In addition, exposure to guava VOCs also increased the indirect defense of citrus by attracting the parasitic wasp Tamarixia radiata. Together, our findings indicate that citrus plants can eavesdrop on the VOC cues emitted by neighboring intact guava plants to boost their JA-dependent anti-herbivore activities. The knowledge gained from this study will provide mechanisms underlying citrus-guava intercropping for the ecological management of insect pests.

Highlights

Volatile organic compounds (VOCs), which are continuously produced and emitted by plants into their surroundings, are the crucial signals in long-distance plant-plant communications (Ninkovic et al, 2016)
The number of eggs laid by female A on the guava VOC-exposed plants was reduced but did not show a significant difference compared with the control in the choice test (P = 0.055; Figure 1B)
Current results identified that guava VOCs were able to prime and induce defense responses involving early defense signaling and the production of defense proteins and metabolites in neighboring citrus plants, thereby increasing herbivore resistance

Summary

Introduction

Volatile organic compounds (VOCs), which are continuously produced and emitted by plants into their surroundings, are the crucial signals in long-distance plant-plant communications (Ninkovic et al, 2016). Some plant species can emit high levels of VOCs, such as aromatic compounds and sesquiterpenes, even when they are not damaged or stressed (Sukegawa et al, 2018; Huang et al, 2019) These constitutively emitted VOCs can induce or prime defense responses in neighboring plants, as demonstrated in volatile chemical interactions between weed species and barley (Glinwood et al, 2004; Ninkovic et al, 2009; Dahlin and Ninkovic, 2013), onion and potato (Ninkovic et al, 2013; Vucetic et al, 2014; Dahlin et al, 2015), mint varieties and soybean (Sukegawa et al, 2018), and molasses grass and maize (Tolosa et al, 2019). This study revealed a new mechanism that affects insect pests in intercropping systems These effects only occur in specific combinations of plant species, indicating that the adaptive strategy of the plants exposed to VOCs depends strongly on the emitter’s identity and physiological status (Ninkovic et al, 2016; Kigathi et al, 2019)

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Conclusion