Fire blight resistance, irrigation and conducive wet weather improve Erwinia amylovora winter survival in cankers

Abstract

Erwinia amylovora causes fire blight, a disease responsible for enormous economic losses in the pome fruit-producing areas where it is present. Despite the abundant research on fire blight, information about E. amylovora population dynamics and survival in fire blight cankers and the plant defense responses to this pathogen in the infected bark are limited. In our study, we obtained fire blight cankers in apple, pear, and Asian pear cultivars showing differing resistance to the disease by shoot inoculation with E. amylovora. We collected cankers from irrigated and non-irrigated trees every 3 months in two independent field experiments and analyzed samples by viability digital PCR. We also assessed the expression of pathogenicity-related (PR) genes in the bark of selected apple and Asian pear cultivars. A logistic regression analysis revealed the impact of environmental and host factors on E. amylovora detection rates in cankers. The chances of detecting live E. amylovora cells in cankers increased significantly in those collected from irrigated trees, in July, and/or during an experiment performed in a year with an expected average rainfall when compared to samples from non-irrigated trees, collected in January, and/or during an experiment performed under environmental conditions dominated by drought. We found a positive correlation between the pathogen detection rates in cankers and the host resistance to fire blight that might be explained by lower E. amylovora survival rates in more damaged tissues of susceptible hosts. The genes PR-1, PR-2, PR-5, and PR-8 were induced in the bark surrounding apple and Asian pear fire blight cankers. Our study, involving the analysis of more than 800 canker samples, provides new knowledge about the fire blight disease cycle and lays the foundation for improved fire blight management and eradication strategies in pome fruit orchards.

Fire blight rootstock infections causing apple tree death: A case study in high-density apple orchards with Erwinia amylovora strain characterization

“…In fall 2017, the concentration of E. amylovora in rootstocks might have declined below the limit of detection of PCR (EPPO, 2013;Ham et al, 2022). The 10.1% -28.5% higher rootstock canker incidence in fall 2017, in comparison to the precent of E. amylovora detections with PCR in fall 2016, aligns well with the faster death of susceptible host wood from cankers and lower linked incidence of E. amylovora-positive cankers on their branches (Santander et al, 2022b). Viability digital PCR this work showed that more E. amylovora cells die in cankers on highly susceptible pome fruit tree hosts due to large extent of damage on branches and faster tissue death, thus causing lower detection rates of E. amylovora-positive cankers.…”

“…The life cycle of fire blight pathogen, Erwinia amylovora (Burrill; Winslow et al, 1920) starts by survival in apple wood bark around fire blight canker edges and below the visible canker necrosis (Santander et al, 2019, Santander et al, 2022b. In spring, E. amylovora emerges on the surface of cankers and can be disseminated by insects, rain, or wind to flowers and shoots.…”

Proof of concept for management of shoot blight and fire blight cankers on pear with preventive spray applications of giant knotweed extract

“…When fire blight cankers develop on the trunks, limbs, and rootstock, they can girdle the stem and kill branches, treetop, or whole mature or young trees in highdensity pear orchards. Pear trees are much more susceptible to fire blight in comparison to apple trees (Santander et al, 2022a). Canker damage is much worse on young tree tissues of juvenile trees and cankers can serve as inoculum sources for future infections on mature trees.…”

“…After E. amylovora invades wood tissues from infected flowers and shoots, new fire blight cankers develop on wood, thus repeating the life cycle (Acímovićet al, 2014a, Acímovićet al, 2019a. However, even though cankers have great importance in disease epidemiology, understanding the parts of E. amylovora life cycle on shoots and in fire blight cankers is still limited (Santander et al, 2022a).…”

“…The commercial varieties with the most desirable fruit texture and flavor generally display high susceptibility to infection and destruction by fire blight (Van Der Zwet and Beer, 1995;Montanari et al, 2016;Mertoglu and Evrenososglu, 2017;Paraschivu et al, 2020). In recent work, 'Bartlett' was classified as highly susceptible cultivar to this disease (Santander et al, 2022a), with many other popular commercial pear cultivars like 'Bosc', 'Comice', and 'D'Anjou' being very susceptible to extremely susceptible to fire blight. Overall, bacterial diseases on tree fruit, including fire blight, are harder to control in comparison to fungal diseases.…”