Atratividade de variedades de citros cultivadas no Estado da Bahia sobre a Diaphorina citri Kuwayama (Hemiptera: Sternorrhyncha: Liviidae) e identificação dos compostos orgânicos voláteis emitidos

Abstract

Huanglongbing (HLB) is a citrus disease caused by bacteria of the genus Candidatus which induces blotchy mottling, diminishment of fruit size and irregular fruit maturation, phloem degeneration and abortion of the seeds. Currently, HBL is the most devastating disease of citrus in the world. In Brazil, HLB can be disseminated in the orchards through the insect vector, the psyllid Diaphorina citri or through grafting of contaminated propagative material. There is still no resistant variety to the pathogens and the management of the disease includes the eradication of all symptomatic plants, the use of disease-free seedling produced in insect-proof nurseries and control of D. citri. In Brazil, the disease is restricted to São Paulo, Minas Gerais and Paraná states. The state of Bahia is considered HLB-free area, even though the state presents all of the suitable conditions for the occurrence of the disease. Therefore, the objective of this study was to evaluate the attractiveness of citrus varieties grown in the State of Bahia on Diaphorina citri and to identify the volatile organic compounds emitted. For this purpose, the following varieties were analysed: 'Valencia', 'Westin' and 'Pera' sweet orange scions (Citrus sinensis Osbeck) and the rootstocks, ‘Rangpur lime’ (Citrus limonia Osbeck), 'Sunki Tropical' (Citrus sunki (Hayata) hort ex. Tanaka), and 'HTR059' (Poncirus trifoliata - hybrid). The 'Flying Dragon' rootstock (Poncirus trifoliata L. (Raf.) was used as the least attractive control and the orange jasmine (Murraya paniculata L. Jack), as the most attractive control to the vector. The olfactometer bioassays were conducted in a four-way olfactometer to identify the most and the least attractive variety to the psyllid and the data obtained were submitted to the Shapiro-Wilk test for normality, and t test for assessing differences between the average of the treatments. The VOCs were extracted according to the SPME technique and identified through GC-MS. The data obtained were evaluated through the principal component analysis (PCA) and hierarchical clustering (HCA) in Metaboanalyst software. The results showed that only the varieties 'Sunki Tropical', ‘Rangpur lime' and 'Valencia' were more attractive than the less attractive control ‘Flying Dragon’. Regarding to the more attractive control orange jasmine, the ‘HTR 059' rootstock was the least attractive. The main compounds found in the least attractive varieties were β-pinene and linalol for 'Pera', β-pinene and decanol for 'Westin', β-caryophyllene and γ- element for 'HTR 059'. In this way, ‘HTR 059’ hybrid and ‘Pera’ and ‘Westin’ sweet orange scions are the varieties indicated to implement actions to prevent the introduction and spread of the disease in the State of Bahia. The Valencia sweet orange and the 'Sunki Tropical' and ‘Rangpur lime' rootstocks were the most attractive cultivars, and therefore less suitable for cultivation in Bahia when HLB prevention is required.