Fire Blight Bactericide Shows Low Resistance Risk in Xinjiang Pear Orchards

The bactericide zhongshengmycin, used in Xinjiang for more than 30 years to control bacterial plant diseases, currently faces a low resistance risk from Erwinia amylovora, the pathogen behind pear fire blight.

Fire blight is one of the most destructive bacterial diseases of pear, causing significant economic losses in production. Because zhongshengmycin has been a recommended control agent in Xinjiang for decades, the research team set out to quantify whether prolonged use had already eroded its effectiveness and to assess the likelihood that resistant strains could spread in the field.

To build the baseline, the team used the broth microdilution method to test 131 isolates of E. amylovora. The results split into two groups: 80 strains were classified as sensitive and 51 as showing low resistance. Across all isolates, the mean concentration needed to inhibit half of growth, the EC50, was 8.34 plus or minus 3.88 micrograms per milliliter, a value now established as the sensitivity baseline against which future shifts in the population can be measured.

The relatively low frequency of isolates with even reduced sensitivity led the authors to conclude that resistance risk in the field is currently low, supporting the continued use of zhongshengmycin for fire blight management.

Resistance, however, can be forced into existence in the laboratory. Through stepwise domestication, gradually exposing the bacterium to increasing concentrations of the antibiotic, the researchers obtained four resistant mutants. These mutants displayed resistance factors ranging from 61.92 to 7,611.20, meaning that some could tolerate thousands of times more drug than their parental strains. Such high resistance factors indicate that the pathogen carries genetic capacity for resistance evolution, even if it has not yet become widespread in orchards.

A key question for any resistance management program is whether resistance to one agent automatically undermines other control options. In cross-resistance assays, the team found no cross-resistance between zhongshengmycin and two alternative bactericides, kasugamycin and copper oxychloride, with correlation coefficients below 0.75 in absolute value. In practical terms, rotating zhongshengmycin with these unrelated agents should not select for strains that evade all of them simultaneously.

Resistance often comes at a cost, and the study confirmed this pattern. The resistant mutants showed significantly reduced survival fitness compared with their parental strains. Reduced fitness suggests that, in the absence of continued drug pressure, resistant variants may be less competitive in the field, further tempering the immediate resistance threat.

The authors caution that a low current risk does not justify complacency. Alongside the baseline data, they recommend implementing science-based application strategies, including rotation with non-cross-resistant agents, to preserve the long-term efficacy of zhongshengmycin. The defined sensitivity baseline now provides growers and plant health authorities in the region with a quantitative reference point for monitoring whether EC50 values drift upward over successive seasons, an early warning signal that resistance is beginning to establish itself in the pathogen population.

Subject of Research: Sensitivity baseline and resistance risk of the pear fire blight pathogen Erwinia amylovora to the bactericide zhongshengmycin

Article Title: Sensitivity baseline and resistance risk assessment of Erwinia amylovora to zhongshengmycin

Article References: Yu, R., Qu, M., Jiang, F., Liu, Q., Wen, Y., & Chen, J. (2026). Sensitivity baseline and resistance risk assessment of Erwinia amylovora to zhongshengmycin. BMC Biotechnology. https://doi.org/10.1186/s12896-026-01229-8

Image Credits: AI Generated

DOI: 10.1186/s12896-026-01229-8

Keywords: Erwinia amylovora, fire blight, zhongshengmycin, antibiotic resistance, pear, sensitivity baseline, cross-resistance, kasugamycin, copper oxychloride, plant pathology, Xinjiang, bactericide