Cucumber Disease Shows Genetic Uniformity, Promising Resistance StrategiesCucumber Disease Shows Genetic Uniformity, Promising Resistance Strategies Bacterial spot, caused by the pathogen *Xanthomonas cucurbitae*, has a devastating impact on cucumber fruit, leading to yield losses and potential rot. However, new research from the University of Illinois Urbana-Champaign reveals a surprising lack of genetic diversity in the pathogen’s genome. Genetic Similarity Over Time and Space By comparing the genomes of bacterial spot samples from 1926 and 2012-2013, researchers discovered that they were remarkably similar, with an identity of over 99%. This uniformity suggests that the pathogen has faced little evolutionary pressure, making it vulnerable to resistance strategies. Implications for Disease Resistance The lack of genetic diversity within the pathogen indicates that resistant plant cultivars could be highly effective in combating bacterial spot. Breeders can focus their efforts on developing resistance in new crop varieties, potentially minimizing the impact of the disease. Management Strategies and Future Directions The findings could also inform management practices, such as the use of antimicrobial sprays. Researchers believe that knowing the genetic makeup of the pathogen will help predict the effectiveness of such strategies in the long term. The study highlights the potential for genomic characterization in understanding the dynamics of plant pathogens and developing sustainable disease management solutions.
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Bacterial spot causes small lesions on cucumber fruit, resulting in yield losses when conditions are right. New research from the University of Illinois Urbana-Champaign shows that there is little diversity in the pathogen’s genome over time or space. The results suggest that finding cucumber germplasm with resistance to the disease could be highly effective.
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Photo: Sarah Hind, University of Illinois Urbana-Champaign
URBANA, Ill. — The pathogen that causes bacterial spot is very good at what it does. It forms small lesions on the skin of squash, melons, cucumbers and other cucurbits, marring the appearance of the fruit and carrying secondary pathogens that lead to rot and severe yield loss. The bacterium, Xanthomonas cucurbitaeis so successful that it has had no reason to evolve through time or space, according to new research from the University of Illinois Urbana-Champaign that characterizes the pathogen’s genetic diversity in the Midwest.
“Earlier we have the Xanthomonas cucurbitae genome from a sample taken in New York in 1926. In our current study, we sequenced the genomes of samples taken in 2012 and 2013 by our collaborators in the Midwest. All of the genomes were actually quite similar, more than 99% identical, but one isolate from Michigan was 99.9% identical to that 1926 isolate. Our results show that there has been very little pressure on this pathogen to evolve,” said Sarah Hind, an assistant professor in the Department of Crop Sciences, part of the College of Agricultural, Consumer and Environmental Sciences (ACES) at Illinois.
The surprising result suggests the pathogen is a one-trick pony. It grows reliably under specific conditions — warm and wet — and otherwise lurks quietly in the background. But the genetic uniformity could be good news for breeders looking to develop resistant crops.
“If we could deploy a resistant plant population, that should be quite effective against what they would likely encounter, at least in the Midwest and probably much of the U.S., because there’s not a lot of diversity in the pathogen populations,” she said.
Hind says there is currently no known resistance in commercially available cucumber crops, but she and her collaborators found bacterial spot resistance in experimental squash and zucchini lines in a 2021 study. Still, she says they need to screen many more varieties before breeding efforts for resistance can begin in earnest.
In addition to opening up potential avenues for developing disease-resistant cucurbits, the findings could inform current and future management strategies. For example, Hind says, bacterial spot doesn’t respond particularly well to industry-standard copper antimicrobial sprays. Knowing more about the pathogen’s genetic potential could predict whether such management strategies will be effective in the long term.
The study, “Comparative genomics of Xanthomonas cucurbitae isolates collected from pumpkin fields in the Midwestern United States,” is published in Plant pathology (DOI: 10.1111/ppa.13965). The research was supported in part by the USDA National Institute of Food and Agriculture.
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