Red mite (Panonychus citri) attack amplifies citrus rootstock-driven responses in physiological and biochemical traits, VOC emission, and expression of defence-related genes in mandarin scions

TOMMY RIOJA^1*KARINA B RUIZ²RICARDO CEBALLOS³

• ¹University of Tarapacá, Arica, Chile
• ²Universidad Arturo Prat, Iquique, Chile
• ³Instituto de Investigaciones Agropecuarias, Santiago, Chile

Citriculture faces several limitations in expanding its surface to new environments and agroecological conditions. However, grafting techniques and tolerant rootstocks have facilitated its development. Plants also produce several metabolites to defend themselves from herbivores; however, little information is available on whether rootstocks affect these defences. To this aim, we evaluated 18-month-old 'W. Murcott' plants grafted onto 'Macrophylla', 'C35', 'Citrumelo', and 'Carrizo citrange' rootstocks in response to infestation by the red mite Panonychus citri. Seven days after infestation, the number of P. citri eggs ranged between 100 to 160 eggs/leaf. The malondialdehyde, proline and salicylic acid contents were differentially affected by both rootstock and P. citri. Physiological parameters associated with photosynthesis, like net assimilation, and chlorophyll, and sugar contents exhibited a declining trend after herbivory; the same happened with total flavonoids content. Volatile organic compounds were affected by rootstocks and, after infestation, their production was significantly accentuated. Expression of biotic stress-related genes like ABA4, EIN, PRs, GLR, and PITY showed a differential response to mite attack dependent on the rootstock. The highest transcript levels relative to controls was found in the 'W. Murcott/Carrizo citrange' combination, especially regarding EIN and GLR target genes. Results demonstrate the influence of four citrus rootstocks on the physiological and metabolic responses in mandarin scion and how herbivory by P. citri exacerbated them under semi-field conditions.