Systemic resistance in citrus to Tetranychus urticae induced by conspecifics is transmitted by grafting and mediated by mobile amino acids

Recent research suggests that systemic signalling and communication between roots and leaves plays an important role in plant defence against herbivores. In the present study, we show that the oviposition of the two-spotted spider mite Tetranychus urticae in the systemic leaves of citrus rootstock Citrus aurantium (sour orange) was reduced by 50% when a lower leaf was previously infested with conspecifics. Metabolomic and gene expression analysis of the root efflux revealed a strong accumulation of glutamic acid (Glu) that triggered the expression of the citrus putative glutamate receptor (GRL) in the shoots. Additionally, uninfested sour orange systemic leaves showed increased expression of glutamate receptors and higher amounts of jasmonic acid (JA) and 12-oxo-phytodienoic acid in plants that were previously infested. Glu perception in the shoots induced the JA pathway, which primed LOX-2 gene expression when citrus plants were exposed to a second infestation. The spider mite-susceptible citrus rootstock Cleopatra mandarin (C. unshiu) also expressed systemic resistance, although the resistance was less effective than the resistance in sour orange. Surprisingly, the mobile signal in Cleopatra mandarin was not Glu, which suggests a strong genotype-dependency for systemic signalling in citrus. When the cultivar Clemenules (C. clementina) was grafted onto sour orange, there was a reduction in symptomatic leaves and T. urticae populations compared to the same cultivar grafted onto Cleopatra mandarin. Thus, systemic resistance is transmitted from the roots to the shoots in citrus and is dependent on rootstock resistance

Systemic resistance in citrus to Tetranychus urticae induced by conspecifics is transmitted by grafting and mediated by mobile amino acids

Recent research suggests that systemic signalling and communication between roots and leaves plays an important role in plant defence against herbivores. In the present study, we show that the oviposition of the two-spotted spider mite Tetranychus urticae in the systemic leaves of citrus rootstock Citrus aurantium (sour orange) was reduced by 50% when a lower leaf was previously infested with conspecifics. Metabolomic and gene expression analysis of the root efflux revealed a strong accumulation of glutamic acid (Glu) that triggered the expression of the citrus putative glutamate receptor ( GRL ) in the shoots. Additionally, uninfested sour orange systemic leaves showed increased expression of glutamate receptors and higher amounts of jasmonic acid (JA) and 12-oxo-phytodienoic acid in plants that were previously infested. Glu perception in the shoots induced the JA pathway, which primed LOX-2 gene expression when citrus plants were exposed to a second infestation. The spider mite- susceptible citrus rootstock Cleopatra mandarin ( C. unshiu ) also expressed systemic resistance, although the resistance was less effective than the resistance in sour orange. Surprisingly, the mobile signal in Cleopatra mandarin was not Glu, which suggests a strong genotype-dependency for systemic signalling in citrus. When the cultivar Clemenules ( C. clementina ) was grafted onto sour orange, there was a reduction in symptomatic leaves and T. urticae populations compared to the same cultivar grafted onto Cleopatra mandarin. Thus, systemic resistance is transmitted from the roots to the shoots in citrus and is dependent on rootstock resistance

Could Plant Hormones Provide a Reliable Tool for Early Detection of Rhynchophorus ferrugineus (Coleóptera: Curculionidae) Infested Palms?

Rhynchophorus ferrugineus (Olivier) (Coleoptera: Curculionidae) is one of the most important pest of palms worldwide. A serious management problem is the difficulty of detecting early infestation stages, which is critical for successful control. Our main objective has been to characterize the metabolic response of Phoenix canariensis hort. ex Chabaud to R. ferrugineus injury to identify candidate biomarkers for early detection. Mechanical wounding and R. ferrugineus infestation resulted in different patterns of plant hormone and secondary metabolite production: SA and caffeic acid concentrations increased by several orders of magnitude following R. ferrugineus development within the palm 7 days after infestation. These compounds did not change in mechanically wounded palms. Therefore, these substances could be further exploited as early warning signs of infestation

From virus resistance to arthropod susceptibility

Resumen de la ponencia presentada en el Annual Meeting on Crop-arthropod-microorganism interactions (CAMo), celabrado en Ljubljana, January 31st to February 2nd, 201

Citrus defense responses against Tetranychus urticae

En la presente tesis doctoral se han estudiado los mecanismos de defensa de cítricos frente al ataque de T. urticae a diferentes niveles. En primer lugar se analizaron los mecanismos de defensa directa utilizando dos patrones con diferente nivel de susceptibilidad. Se llegó a la conclusión de que la ruta de defensa del ácido jasmónico (JA) es la efectiva frente a la araña roja. Mediante análisis metabolómicos se observó una gran acumulación de diferentes flavonoides como naringenina o hesperetina en el patrón más resistente. Estos flavonoides con posible actividad acaricida posiblemente estén regulados por la ruta JA, fenómeno que se ha confirmado en otras especies vegetales. A continuación se estudió si los volátiles liberados por los cítricos tenían algún efecto sobre las plantas vecinas o sobre el propio fitófago. Los experimentos demostraron que los volátiles del patrón resistente naranjo amargo infestado con T. urticae eran capaces de inducir resistencia en el patrón susceptible mandarino Cleopatra y además que estos volátiles creaban un efecto de repelencia en el fitófago. Se observó que T. urticae evitaba las plantas de naranjo amargo previamente infestadas por conspecíficos. La identificación y cuantificación de los volátiles indicó que estos efectos eran causados por limoneno, ocimeno y 4-hidroxi-4-metil-2-pentanona. La última parte del trabajo se basó en estudios sistémicos para tratar de dilucidar las señales que eran transmitidas desde el patrón a la variedad. Se muestreó el eflujo de la raíz en plantas de la variedad Clemenules injertadas sobre los dos patrones ya citados. Posteriormente el análisis metabolómico de estas muestras indicó que el ácido glutámico parecía ser la señal que se transporta desde el patrón hasta la variedad

Can Plant Defence Mechanisms Provide New Approaches for the Sustainable Control of the Two- Spotted Spider Mite Tetranychus urticae?

Tetranychus urticae (T. urticae) Koch is a cosmopolitan, polyphagous mite which causes economic losses in both agricultural and ornamental plants. Some traits of T. urticae hamper its management, including a short life cycle, arrhenotokous parthenogenesis, its haplodiploid sex determination system, and its extraordinary ability to adapt to different hosts and environmental conditions. Currently, the use of chemical and biological control are the major control methods used against this mite. In recent years, some studies have focused on plant defence mechanisms against herbivores. Various families of plant compounds (such as flavonoids, glucosinolates, or acyl sugars) have been shown to behave as acaricides. Plants can be induced upon appropriate stimuli to increase their resistance against spider mites. This knowledge, together with the understanding of mechanisms by which T. urticae detoxifies and adapts to pesticides, may complement the control of this pest. Herein, we describe plant volatile compounds (VOCs) with repellent activity, and new findings about defence priming against spider mites, which interfere with the T. urticae performance. The use of VOCs and defence priming can be integrated into current management practices and reduce the damage caused by T. urticae in the field by implementing new, more sustainable crop management tools

Different metabolic and genetic responses in citrus may explain relative susceptibility to Tetranychus urticae

Background: Life history parameters of the phytophagous spider mite Tetranychus urticae in citrus depend on the rootstock where the cultivar is grafted. To unveil the mechanisms responsible for this effect, the authors have carried out comparative experiments of T. urticae performance on two citrus rootstocks, the highly T. urticae-sensitive Cleopatra mandarin and the more tolerant sour orange. Results: Sour orange showed reduced leaf damage symptoms, supported lower mite populations and reduced oviposition rates compared with Cleopatra mandarin. Hormonal, metabolomic and gene expression analyses of the main defence pathways suggest a relevant role of the oxylipin and the flavonoid pathways in the response against T. urticae. Sour orange showed an increased activity of the JA pathway, which was hardly active in the most susceptible rootstock. Moreover, treatments with the LOX inhibitor Phenidone abolished the enhanced tolerance of sour orange. Therefore, oxylipin-dependent defence seems to be rootstock dependent. The metabolomic analysis showed the importance of the flavonoid pathway, which is implicated in the interaction between plants and their environment. Conclusion: The findings suggest that sour-orange enhanced tolerance to spider mites can be sustained by a combination of pre-existing and induced responses depending on high levels of flavonoids and a fast and effective activation of the oxylipin pathway

Tetranychus urticae-triggered responses promote genotype-dependent conspecific repellence or attractiveness in citrus

The citrus rootstocks sour orange and Cleopatra mandarin display differential resistance against Tetranychus urticae. Sour orange plants support reduced oviposition, growth rates and damage compared with Cleopatra mandarin plants. Jasmonic acid signalling and flavonoid accumulation have been revealed as key mechanisms for the enhanced resistance of sour orange plants. In this study, we observed that the release of T.urticae herbivore-induced plant volatiles (HIPVs) from sour orange plants has a marked repellent effect on conspecific mites associated with the production of the terpenes -ocimene, -farnesene, pinene and d-limonene, and the green leaf volatile 4-hydroxy-4-methyl-2-pentanone. By contrast, T.urticae HIPVs from Cleopatra mandarin plants promote conspecific mite attraction associated with an increase in (2-butoxyethoxy) ethanol, benzaldehyde and methyl salicylate levels. HIPVs released from sour orange plants following T.urticae infestation induce resistance in Cleopatra mandarin plants, thereby reducing oviposition rates and stimulating the oxylipin biosynthetic gene lipoxygenase2 (LOX2). Cleopatra HIPVs do not affect the response to T.urticae of these rootstocks. We conclude that sour orange plants promote herbivore-induced resistance in Cleopatra mandarin plants and, despite the weak basal resistance of these rootstocks, herbivore resistance can be induced through the combination of HIPVs, such as -ocimene and d-limonene