Where do plant diseases that suddenly appear come from? A disease that is catastrophic in one place is often caused by a bacterial, viral or fungal pathogen from another region of the world where it currently co-exists with plants without drama. It may be that long ago large numbers of those plants did succumb to the disease, and that the current plants are the offspring of the lucky individuals that survived because of slightly different genes that turned out to be disease-resistant. In its home country, a disease may continue to live on plants, but only kill offspring that lack the resistant gene, or individuals weakened by stressors like drought.
soil, wood products, etc.). Suppose it then comes into contact with a population of plants (say oak trees) in North America. If the majority of the trees turn out to be genetically resistant, the non-native pathogen may remain undetected and never cause harm. If large numbers of the trees start dying, however, the disease quickly makes a name for itself! (It’s these kinds of catastrophic diseases that are discussed in this website.) The disease may spread rapidly, wiping out whole populations and altering natural communities as it goes.Halfway across the world, however, the plants are at least slightly different genetically. A pathogen may move across oceans, undetected, on any number of carriers (plants in the nursery trade,
Over hundreds or even thousands of years, the remaining genetically resistant plants may reproduce sufficiently to make a comeback and repopulate the landscape. Humans sometimes speed up the process by propagating and planting disease-resistant plants.