ONE HUNDRED AND ONE YEARS OF RESEARCH ON BACTERIAL WILT
Kelman A.
Department of Plant Pathology, North Carolina State University, Raleigh, N. C.
Since the description by Erwin F. Smith in 1896 of a wilt disease of tomato, eggplant and potato caused by Pseudomonas solanacearum, over 4,000 papers have been published on this disease. The unique characteristics of bacterial wilt delineated in these publications combine to place it in the front rank of diseases caused by phytopathogenic bacteria. It affects over 200 species of plants in a wider range of different genera and plant families than any other bacterial disease, with the possible exception of crown gall. However, more individual plants have been killed by bacterial wilt than by any other bacterial disease of plants. Although searching through the publications on bacterial wilt for landmark contributions presents a challenging assignment, identification of key advances is warranted after a full century of research. The contributions in the listing that follows are not ranked in order of importance, but are selected as examples for possible inclusion in a projected master list: recognition of the relationship between colony type and virulence; rapid loss in virulence in culture; role of extracellular polysaccharide in wilt induction in concert with pectic enzymes and other cellular secretions; the use of a tetrazolium chloride medium for differentiation of colony types; differentiation of strains into biovars based on ability to utilize and oxidize several hexose alcohols and disaccharides and distinctive host ranges; discovery of the production of IAA and ethylene ; discovery that hrp and related genes are involved in control of disease development and induction of the hypersensitive reaction; importance of optimal temperatures in symptom development for specific strains; long distance dissemination in infected tomato transplants, seed tubers of potatoes and rhizomes of bananas; dissemination by pruning knives and by insects on bananas; role of weed hosts in survival of biotypes that affect solanaceous hosts; synergistic interaction between root knot nematodes and P. solanacearum; survival of P. solanacearum in rhizospheres or in roots of symptomless weed species; demonstration of induction of systemic resistance following infiltration of tobacco leaves with avirulent strains; and the discovery of resistance in peanuts in Java and in tobacco in North Carolina. Designation of landmark status to the many rapid advances now being made in the molecular biology and genetics of the wilt pathogen awaits the assessment that can only come with the passage of time.
