Bacterial Diseases That Shape How Crops Are Grown and Traded

Start with a disease named for how it looks: blossoms, shoots and branches blacken and wilt as though scorched, and young trees can die outright. Erwinia amylovora is native to North America and spread to Europe in the twentieth century, and no fully curative treatment exists once a tree is infected.

Xanthomonas citri raises corky lesions on citrus leaves, stems and fruit. Because infected fruit and nursery stock can carry it into new areas, producing regions run strict quarantine and eradication programs, including the large scale tree destruction campaigns in Florida in the early 2000s.

Also called citrus greening, this disease is caused by phloem limited Liberibacter bacteria and carried by the Asian and African citrus psyllids. It has no known cure and has devastated citrus industries in Florida, Brazil and parts of Asia since the early 2000s.

Xylella fastidiosa, spread by sharpshooter insects, blocks the water conducting tissue of grapevines and can kill a vine within one to five years. It devastated vineyards in Southern California in the nineteenth century, and related strains of the same bacterium now threaten olive groves in Europe.

Ralstonia solanacearum lives in the soil and causes rapid, often fatal wilting in potato, tomato, eggplant, banana and many other crops. Its very wide host range, long soil persistence and multiple aggressive races make it one of the hardest bacterial plant diseases to manage.

Xanthomonas oryzae pv. oryzae produces water soaked lesions along rice leaf margins and can cut yields by up to 50 percent in susceptible varieties under warm, humid conditions. First identified in Japan in the late nineteenth century, it has been a major target of resistance gene breeding.

Xanthomonas campestris pv. campestris causes V shaped yellow lesions on the leaf margins of cabbage, broccoli and cauliflower. Because it is seedborne and spreads fast through transplant production, certified disease free seed is central to managing it worldwide.

End with a disease whose mechanism became a tool. Agrobacterium tumefaciens causes tumor like galls on a very wide range of woody and herbaceous plants by transferring a piece of its own DNA into the host genome, a natural gene transfer later adapted into a standard method of plant genetic engineering.