Genetic diversity and aggressiveness of Erwinia psidii on Eucalyptus spp. in Brazil

Abstract

The genetic variability and aggressiveness of Brazilian Erwinia psidii isolates from Eucalyptus spp. was studied and compared with reference isolates from guava (Psidium guajava). Repetitive element sequence (rep)‐based PCR markers of 101 isolates from Eucalyptus spp. and five from guava showed that the populations of E. psidii displayed a relatively low genetic variability. No correlation of genetic clustering based on rep‐PCR analysis with geographic origin or host of origin was observed, indicating that genome rearrangements associated with adaptation to a particular host were not detected by these molecular markers. A higher genotypic richness was detected in the Mato Grosso do Sul population, probably reflecting a pathogen dissemination associated with the recent expansion in eucalypt plantations. Wilcoxon and ANOVA tests of disease severity data indicated differences in aggressiveness among isolates and an isolate × clone interaction. The area under the disease progress curve (AUDPC) and disease severity for some isolates were significantly different between two susceptible clones tested. Notably, isolate LPF681 from guava was not able to cause disease on a susceptible Eucalyptus urophylla clone, suggesting that some co‐evolution between pathogen and host has taken place. The variability in aggressiveness and virulence among isolates of E. psidii observed in this study will be important for the establishment of appropriate screening approaches to select for disease resistance.

An agglutination test for fast and specific detection of Erwinia psidii

“…and three from P. guajava obtained in 13 different localities from the states of Mato Grosso do Sul, Rio Grande do Sul and São Paulo, the three major eucalypt producers in Brazil, were agglutinated by the anti‐ Ep antibody. These results are consistent with the high genetic homogeneity observed in the E. psidii population from those three states as assessed by rep‐PCR (Montoya‐Estrada et al, ). Importantly, even isolates LPF554 and LPF610, which are genetically very divergent with respect to other isolates (Montoya‐Estrada et al, ), were agglutinated by the antibody, suggesting that it recognizes a highly conserved epitope.…”

“…These results are consistent with the high genetic homogeneity observed in the E. psidii population from those three states as assessed by rep‐PCR (Montoya‐Estrada et al, ). Importantly, even isolates LPF554 and LPF610, which are genetically very divergent with respect to other isolates (Montoya‐Estrada et al, ), were agglutinated by the antibody, suggesting that it recognizes a highly conserved epitope. Such an epitope seems not to be present in other pathogenic and non‐pathogenic bacterial species naturally associated with eucalypt plants.…”

Host range ofErwinia psidiiand genetic resistance ofEucalyptusandCorymbiaspecies to this pathogen

“…Additionally, the possibility that there were differences in the effector complement between the E. psidii strains used in the two studies cannot be ruled out. This hypothesis is supported by the differential interactions observed between E. psidii isolates and distinctEucalyptus clones in a previous study(Montoya-Estrada et al, 2018).…”

“…Such an apparent high specificity of E. psidii towards the Myrtaceae family is not surprising considering the recent reports of this pathogen on Eucalyptus and Psidium species. It is likely that a long coevolutionary process between the pathogen and its host plants has not yet occurred, an interpretation that is supported by the low genetic diversity observed in the E. psidii population obtained from states that are the major eucalypt producers in Brazil (Montoya‐Estrada et al, ). Most of the Myrtaceae species evaluated in this study, other than some species of Eucalyptus and Corymbia , are not commercially exploited as crops and are instead found as small populations under natural conditions.…”

“…The LPF534 strain of E. psidii used in this study was isolated from Eucalyptus dunnii in Guaíba (Rio Grande do Sul, Brazil) and belongs to the culture collection of plant pathogenic bacteria of the Forest Pathology Laboratory/Bioagro at the Universidade Federal de Viçosa (CPBFPL-UFV). This strain was previously confirmed to belong to E. psidii by biochemical and molecular analyses (Arriel et al, 2014) and was shown to be highly virulent on Eucalyptus (Montoya-Estrada et al, 2018). Erwinia psidii was routinely grown on solid 523 medium at 28°C for 24 hr (Kado & Heskett, 1970).…”