Plant-Microbe Interactions: Life and Death at the Interface.

Abstract

Interactions between microorganisms and plants have undoubtedly had major effects on the development of civilization since humans began to rely extensively on cultivated crops for food. Indeed, ancient chronicles of famines, plagues, and epidemics show that some of the more serious plant diseases, such as rusts, smuts, and mildews, were recognized soon af? ter the emergence of organized agriculture. Theophrastus (~371 to 287 bc) described disease symptoms on a number of plants used for food and the Romans paid tribute to appease the rust god Robigo. More recently, plant disease outbreaks have resulted in catastrophic crop failures that have triggered famines and caused major social change. The effects of such epidemics have been particularly devastating in situations such as the Irish potato famine of the 1840s, in which communities depended on a single crop as their primary food source. The potential for se? rious crop disease epidemics still persists today, as evidenced by recent outbreaks of Victoria blight of oats and southern corn leaf blight. These diseases result from agricultural practices that rely on monoculture crops?planting closely related crop species over wide geographical areas provides, in effect, a large Petri dish for the evolution of increasingly virulent patho? gen forms. In addition to causing food shortages, microbial interactions with plants can directly affect the health of humans and livestock. One notable example is ergot poisoning, caused by toxins in the fruiting bodies of the fungus Claviceps purpurea, which can contaminate rye flour. These toxins cause a frightening syndrome typified by hallucinations, burning sensations, miscarriages, gangrene, and, in severe cases, death. The affliction, known as St. Anthony's fire or Holy fire, was most prevalent in the Middle Ages; present day outbreaks are only prevented by the strict cultural and sanitary standards that are now applied in the regulation of grain sales. Further problems resulting from the presence of allergens, carcinogenic com? pounds, and various mycotoxins in moldy grain, peanuts, and animal feed have recently been shown to affect human health. For readers interested in more fundamental information, a broad coverage of plant pathology is provided in the text by