Newswise — The Vidalia onion, a distinctive sweet variety, is protected by trademark and can only be cultivated in specific counties in Georgia as mandated by law. Unfortunately, these highly prized onions face a significant threat from the bacterial pathogen Pantoea ananatis, which causes severe damage by causing rot in both the onion bulbs and leaves. As a result, onion growers in Georgia suffer substantial losses, as there are currently no disease-resistant cultivars available to combat this issue. The bacterium produces a plant toxin called pantaphos, which is responsible for the rotting symptoms in onions. Within the bacterium, a cluster named HiVir (high virulence) contains eleven genes that produce this toxin. However, the precise roles of most of these genes within the cluster in the bacterial pathogenesis remain unknown, leaving much to be discovered about how this bacterium infects onions.
In response to this critical plant disease, Dr. Brian Kvikto and Dr. Bhabesh Dutta from the University of Georgia have initiated an intensive research program. Recently, Dr. Gi Yoon (Gina) Shin, leading a study in Dr. Kvikto's laboratory, has successfully identified the essential genes within the HiVir cluster and determined which genes contribute partially to this disease.
A recent publication in Molecular Plant-Microbe Interactions (MPMI) has shed light on the HiVir gene cluster, which is commonly found in many P. ananatis strains that are pathogenic to onions. The study discovered that natural mutations occurring in these essential genes render them ineffective in causing onion infections. The researchers in the laboratory devised an ingenious assay to isolate the toxin produced by the pathogen. Dr. Shin elaborates that when this toxin is applied to plants other than onions, it induces the formation of lesions. This observation suggests that the toxin produced by P. ananatis might possess broad-spectrum activity, potentially targeting conserved functions or pathways within the plant.
Although the precise mechanism by which this toxin induces lesions on different plants is still unknown, Dr. Shin affirms, "Identifying the specific target of the toxin holds great promise for facilitating the development of pantaphos-resistant onion cultivars. Such a breakthrough would effectively mitigate the economic losses faced by the onion industry." This study offers exciting insights that bring us closer to the goal of producing disease-resistant Vidalia onions.
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