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First Report of ‘Candidatus Phytoplasma pyri’ on Pear in Chile

    Affiliations
    Authors and Affiliations
    • R. Facundo
    • N. Quiroga
    • P. Méndez
    • A. Zamorano
    • N. Fiore , Universidad de Chile, Facultad de Ciencias Agronómicas, Departamento de Sanidad Vegetal, La Pintana, Santiago, Chile.

      Pear decline (PD) is one of the most devastating diseases that affects pear trees and it has been detected in the Mediterranean basin and in the United States. The causal agent is ‘Candidatus Phytoplasma pyri’ (‘Ca. P. pyri’), belonging to the apple proliferation group (16SrX), ribosomal subgroup C. Cacopsylla pyri L. has been found as the main vector in European countries, while in the United States and U.K., the phytoplasma can be naturally spread by Cacopsylla pyricola (Förster). In Chile, pear production has been increasing since 2006, in direct relation with the introduction of European cultivars. During the beginning of autumn 2014, in one pear orchard planted in 2012 located in Biobío Region in the central zone of Chile, 26 out of 1,120 trees (cv. Williams on quince BA29 rootstock) showed a remarkable decline with reddening of leaves and branch phloem necrosis. Samples from eight plants with symptoms and two asymptomatic plants were collected. Total nucleic acids were extracted from 1 g of a mixture of midribs and petioles of leaves, using phenol-chloroform method (Prince et al. 1993). Phytoplasma detection was performed using universal nested PCR primer pairs for two target genes: P1/P7 and F2n/R2 for 16S rRNA gene (Gundersen and Lee 1996; Schneider et al. 1995) and Tuf340/Tuf890 followed by Tuf400/Tuf835 for tuf gene (Makarova et al. 2012). Positive results were obtained only in symptomatic samples after nested amplification, obtaining a 1,250 and 450 bp amplicon for 16S rRNA and tuf genes, respectively. All amplified fragments showed an identical nucleotide sequence that was deposited in GenBank under accession numbers KX644930 (16S rRNA gene) and KX644931 (tuf gene). Both genes sequences showed 100% nucleotide identity with isolate PD1 from Germany (AJ542543 and JQ824247 for 16S rRNA and tuf genes, respectively). Additionally, restriction fragment length polymorphism analysis was carried out in order to confirm phytoplasma identification. After digestions with TruI and SspI (16S rRNA sequence) and TruI (tuf sequence), the profiles obtained were identical to those observed for ‘Ca. P. pyri’ reference isolates (Makarova et al. 2012; Seemüller and Schneider 2004). This is the first report of ‘Ca. P. pyri’ in Chile and South America. Currently, survey is being extended to other commercial pear tree orchards and nurseries to obtain more information about the spread and origin of ‘Ca. P. pyri’ in Chile. At the same time, epidemiological studies are in progress to identify the possible presence of insect vectors, considering that in Chile, C. pyri and C. pyricola have never been found.

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      This study was funded by National Fund for Scientific and Technological Development (FONDECYT), Chile (No. 1140883).