First Report of Xylella fastidiosa in Avocado in Costa Rica

Abstract

Since the late 1990s, chlorotic mottling, marginal scorch, deformation of leaves, defoliation, shortening of internodes, and branch dieback have been observed in avocado trees (Persea americana Mill.) in Costa Rica. The symptoms are not uniformly distributed in the tree, so some branches are symptomatic while others are not. These symptoms are similar to several leaf scorch diseases caused by the bacterium Xylella fastidiosa Wells (2,4). This bacterium has been detected in coffee and citrus plants in Costa Rica. Of 227 avocado trees tested by double-antibody sandwich (DAS)-ELISA with X. fastidiosa specific antiserum (Agdia Inc., Elkhart, IN) from 2000–2004, 188 were positive. Results of ELISA tests of individual trees varied with the season and branches tested. Fifteen greenhouse-grown, ELISA-negative avocado seedlings were grafted with budwood from an ELISA-positive tree. Eight of these developed scorch symptoms and one also showed chlorotic mottling and deformation, showing that the disease is graft transmitted. All of these features are characteristic of diseases caused by X. fastidiosa (2,4). Transmission electron microscopy of leaf petioles from three field trees positive by ELISA, revealed rod-shaped bacilli approximately 1.6 to 2.0 μm long and 0.3 μm in diameter with a rippled cell wall inside xylem vessels and embedded in a matrix; morphology and measurements that are consistent with those reported for X. fastidiosa (2). DNA extraction and PCR attempts have been limited by mucilaginous sap from avocado. Positive PCR results (approximately 472-bp band) were obtained from two of the grafted seedlings and seven field trees from two distinct geographical locations (Alajuela and San José provinces) with DNA extractions from the plant sap using DNeasy Plant Mini Kit (Qiagen GmbH, Hilden, Germany) following a modified protocol (1) and nested PCR (3). Four of the PCR products, including one from the grafted seedlings, were cloned and sequenced in duplicate. GenBank sequences EU021997 to EU022000 present 99 to 100% sequence identity to a Pierce's disease strain from California (Temecula1) and 94 to 95% to a citrus variegated chlorosis strain from Brazil (Found-5). Several attempts have been made to isolate the bacterium in ‘periwinkle wilt’ and buffered cysteine-yeast extract media with negative results, probably because of the rapid production of mucilaginous sap when the avocado tissues were sampled. To our knowledge, this is the first report of X. fastidiosa in avocado trees. References: (1) M. J. Green et al. Plant Dis. 83:482, 1999. (2) S. S. Hearon et al. Can. J. Bot. 58:1986, 1980. (3) M. R. Pooler and J. S. Hartung. Curr. Microbiol. 31:377, 1995. (4) A. H. Purcell et al. Phytopathology 89:53, 1999.

Living in two Worlds: The Plant and Insect Lifestyles ofXylella fastidiosa

“…The most economically important diseases caused by X. fastidiosa are Pierce's disease of grape (PD) and citrus variegated chlorosis (CVC) of citrus species, both of which have received more attention by far than the many other diseases caused by this pathogen. Alfalfa, peach, plum, almond, elm, coffee, sycamore, oak, maple, pear are among the many other plant species for which diseases caused by X. fastidiosa are described, and the pathogen can be detected in hundreds of asymptomatic plant species (14,27,57,59,60,62,64,65,78,83,93,125). This pathogen is obligately vector-transmitted from one plant to another by various xylem sap-feeding insects.…”

“…For this reason, the study of PD has dramatically increased since the last reviews of this pathogen, which focused mostly on descriptions of symptom development and etiology of disease (64,65,93). Perhaps due to the increasing attention to this pathogen, as well as better means of detection and discrimination of its many strains, this pathogen is being detected in large numbers of new host plant species in California and elsewhere (27,60,78,83); whether these numbers represent a broadening of its host range due to pathogen evolution or introduction of novel strains, or simply an appreciation of is exceptionally wide host range is unknown. Like-wise, the outbreak of CVC in Brazil has also stimulated extensive study of the strains that cause that disease, and led to the complete sequencing of the genome of a CVC strain of X. fastidiosa, the first plant pathogenic bacterium to be sequenced (111).…”

Bacterial Leaf Scorch, a New Blueberry Disease Caused by Xylella fastidiosa

“…Several reports in the past few years have revealed that X. fastidiosa is associated with diseases in a growing number of plant hosts (Almeida et al, 2005;Baumgartner and Warren, 2005;Hernandez-Martinez et al, 2007;Montero-Astua et al, 2008;Myers et al, 2007;Randall et al, 2007). No reports, however, specifically describe the aforementioned blueberry disease.…”

“…Almeida et al (2005) showed that Homalodisca coagulata was able to inoculate X. fastidiosa into dormant grapes, although field acquisition experiments did not result in transmission. Montero-Astua et al (2008) reported the finding of X. fastidiosa in avocado plants in Costa Rica based on the positive results of enzyme-linked immunosorbent assay (ELISA) and PCR, although attempts to cultivate the bacterium in periwinkle wilt (PW) medium (Davis et al, 1981) and buffered charcoal yeast extract medium (Feeley et al, 1979;Raju et al, 1982) were negative.…”

Susceptibility ofPhoenix roebeleniitoXylella fastidiosa

“…Hopkins, ; Purcell and Saunders, ; Hopkins and Purcell, ), while in other plants, it can be a serious pathogen causing a wilting or scorching disease (EFSA PLH Panel, ). X. fastidiosa is reported from many countries and from a great number of host plants including important tree crops like coffee (Rodriguez et al., ), citrus (Hartung et al., ; Aguilar et al., ), avocado (Montero‐Astua et al., ) and grapevine (Hill and Purcell, ; Aguilar et al., ). It can also infect many ornamental plants, like Nerium oleander (Oleander, Purcell et al., ; Montero‐Astua et al., ) and Polygala myrtifolia (Saponari et al., ; Martelli, ).…”