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A Phytoplasma Closely Related to the Pigeon Pea Witches'-Broom Phytoplasma (16Sr IX) Is Associated with Citrus Huanglongbing Symptoms in the State of São Paulo, Brazil

First, second, third, fifth, and sixth authors: Fundecitrus, Araraquara, SP, CEP 14807-040, Brazil; fourth author: Universidade de São Paulo, CEP 13418-900, Piracicaba, SP, Brazil; and seventh, eighth, and ninth authors: Institut National de la Recherche Agronomique and Université de Bordeaux 2, UMR 1090, BP 81, 33883 Villenave d'Ornon, France.

In February 2007, sweet orange trees with characteristic symptoms of huanglongbing (HLB) were encountered in a region of São Paulo state (SPs) hitherto free of HLB. These trees tested negative for the three liberibacter species associated with HLB. A polymerase chain reaction (PCR) product from symptomatic fruit columella DNA amplifications with universal primers fD1/rP1 was cloned and sequenced. The corresponding agent was found to have highest 16S rDNA sequence identity (99%) with the pigeon pea witches'-broom phytoplasma of group 16Sr IX. Sequences of PCR products obtained with phytoplasma 16S rDNA primer pairs fU5/rU3, fU5/P7 confirm these results. With two primers D7f2/D7r2 designed based on the 16S rDNA sequence of the cloned DNA fragment, positive amplifications were obtained from more than one hundred samples including symptomatic fruits and blotchy mottle leaves. Samples positive for phytoplasmas were negative for liberibacters, except for four samples, which were positive for both the phytoplasma and ‘Candidatus Liberibacter asiaticus’. The phytoplasma was detected by electron microscopy in the sieve tubes of midribs from symptomatic leaves. These results show that a phytoplasma of group IX is associated with citrus HLB symptoms in northern, central, and southern SPs. This phytoplasma has very probably been transmitted to citrus from an external source of inoculum, but the putative insect vector is not yet known.

Additional keywords:PCR detection, plant-pathogenic mollicute.