Molecular characterization and diversity of phytoplasmas in citrus orchards in the Sao Paulo state

Author(s)

Júlio César Barbosa

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2011-03-01

Examining board members

Armando Bergamin Filho; Lilian Amorim; Renato Beozzo Bassanezi; Ivan Paulo Bedendo; Helvecio Della Coletta Filho

• Advisor: Armando Bergamin Filho

Abstract

Recently a phytoplasma of the 16SrIX group was associated with citrus trees exhibiting symptoms of huanglongbing (HLB) in Sao Paulo state. However, due to the wide diversity of phytoplasmas that have been observed in several crops in Brazil, it is possible that in addition to the phytoplasma of group 16SrIX other phytoplasmas could also be associated with citrus trees. Therefore, the objective of this study was to investigate if others phytoplasmas besides that of the 16SrIX group are associated with citrus plants in the São Paulo state. Leaf samples from citrus trees, weeds and cicadellids were collected between June and October of 2010 from citrus orchards of four municipalities of the Sao Paulo state: Araraquara, Bebedouro, Piracicaba and Taquarituba. Nested PCR analysis revealed the presence of phytoplasmas associated with citrus trees (symptom: leaf chlorosis), weeds: Bidens pilosa (symptoms: phyllody and virescence), Leonorus sibiricus (symptom: leaf distortion), Solanum americanus (symptom: witches broom), Erigeron bonariensis (symptoms: redning and witches broom) e Euphorbia heterophylla (symptom: leaf distortion); and cicadellids of specie Agallia albidula (Uhler, 1895) (subfamily Agalliinae). The confirmation of the phytoplasma presence and molecular characterization was carried out by RFLP analysis and sequencing of the 16S rDNA region. A wide diversity of phytoplasmas was verified. Phytoplasmas of the 16SrIII and 16SrIX groups were associated with citrus trees in Piracicaba, while a phytoplasma of the 16SrVII group was associated with citrus trees in Bebedouro. Phytoplasmas of the 16SrIII group were associated with weeds belonging to the species B. pilosa, S. americanus and L. sibiricus in Piracicaba and a phytoplasma of the 16SrVII group was identified associated with plants of E. bonariensis and E. heterophylla in Piracicaba and Taquarituba, respectively. A phytoplasma of the 16SrIII group was associated with A. albidula in Taquarituba, suggesting that this cicadelid is a potential vector of phytoplasmas in citrus orchards. Based on the analysis of the 16S rDNA region, many of the found phytoplasmas are distinct from those already reported. Due to this distinction, these phytoplasmas were proposed as representatives of new subgroups of the groups 16SrIII, 16SrVII and 16SrIX. The results of this study dont allow us associate the found phytoplasmas with HLB or any other described disease. Thus, more studies are needed to identify the role of theses phytoplasmas as pathogens of citrus trees and weeds. (AU)