Murta (Ugni molinae Turcz.) and common chaura (Gaultheria phillyreifolia (Pers.) Sleumer) are native species of Chile. Plants of both species have shown over-branching like witches' broom. The causal agents of these symptoms in many plants are phytoplasma. To verify the presence of these microorganisms, DAPI (4',6-diamidino-2-phenylindole) staining analysis and polymerase chain reaction (PCR) were performed in symptomatic and asymptomatic plants. Positive PCR samples were sequenced to identify the pathogens involved. In individuals of both species with witches' broom symptoms, DAPI staining showed fluorescent bodies in the phloem tissues, but not in asymptomatic plants. Verification by nested-PCR, phytoplasmatic DNA was amplified from diseased murta and chaura, but not in apparently healthy plants. Sequencing of amplified products allowed locating phytoplasma within the ash yellows group (16SrVII) and related to Candidatus phytoplasma fraxini. This is the first report of phytoplasma in Chilean native species. Considering the diversity of plant species infected by the ash yellows group suggests that G. phillyreifolia and U. molinae could be a phytoplasma reservoir for other economically important agricultural crops.

RESUMENLa murta o murtilla (Ugni molinae Turcz., Myrtaceae), es un arbusto frutal siempre verde, nativo de Chile. Su fruto es una baya globosa muy aromática y sabrosa, de gran potencial en consumo fresco e industrializado. El arbusto presenta en el follaje una enfermedad caracterizada por una incontrolable ramificación conocida como "escoba de bruja", siendo la más común y destructiva, la cual podría estar relacionada con un agente biótico. Se realizaron cortes histológicos en tejidos con y sin síntomas de la enfermedad, los cuales se visualizaron mediante microscopía electrónica de transmisión. Se observó la presencia de microorganismos pleomórficos similares a fitoplasmas en los tejidos del floema en plantas enfermas. Pruebas moleculares mediante PCR permitieron confirmar la presencia de estos procariontes en tejidos enfermos, pero no en plantas asintomáticas, lo cual sugiere que estos microorganismos podrían estar asociados como agentes causales de la enfermedad escoba de bruja en murta. En futuros trabajos se espera obtener la identificación de este fitoplasma, sus vectores y dispersión en el sur de Chile. Palabras clave: Myrtaceae, molicutes, diagnosis, TEM, PCR. ABSTRACT Microscopic and molecular evidence of phytoplasma in murta plants (Ugni molinae Turcz.) affected by witches'-broom diseaseThe murta or murtilla (Ugni molinae Turcz., Myrtaceae) is an evergreen shrub fruit native to Chile. Its fruit is an aromatic and tasty globose berry, great potential as a fresh product and for industrialized production. The most common and destructive disease of the foliage of this shrub is characterized by uncontrolled branching and known as "witches'-broom" disease; this could be related to a biotic agent. Histological cuts were made in tissues with and without symptoms of the disease, which were visualized by transmission electron microscopy. Pleomorphic microorganisms similar to phytoplasma in phloem tissue of diseased plants were seen. PCR molecular testing confirmed the presence of these prokaryotes in diseased tissues, but not in asymptomatic plants, suggesting that these microorganisms could be associated as causal agents of witches'-broom disease in murta. Future research is expected to identify this phytoplasma, its vectors and its dispersion in southern Chile.

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