Discovery of plant pathogenic bacteria: dispute and controversy between America and Europe.

The demonstration of a bacterial cause of some plant diseases has been clai med few years after it was commonly recognized that bacteria were able to c ause diseases of human and animal. Nevertheless. some sharp controversies t ook place, between German and American specialists (1897-1901). before the existence of bacterial diseases of plants was accepted by all phytopatholog ists. Nowadays. about 350 bacteria are described, which infect plants: they are pathovars, or subspecies, belonging to 21 genera, Bacterial diseases o f plants can be classified into three major categories according to the typ e of symptoms shown by the infected plant: necrosis and wilt, soft-rot, tum our. The interaction between bacteria and plant cells is usually establishe d from the apoplast, although SOI-ne bacteria are xylem or phloem limited, This interaction involves an original protein secretion system (which is al so described in bacteria pathogenic for animals), hydrolytic enzymes (pecti nases, cellulases), toxins and/or phytohormones, Bacteria of one group (Agr obacterium) modify the plant metabolism after gene transfer from a plasmid. on the economic and social point of view, these diseases may be limiting f actors of some key-productions (rice, cassava). In addition, they play a ro le in reducing the quality of agricultural products (reduced growth, spots on leaves and fruits). Control of bacterial diseases is limited, It relies usually on a combination of prophylaxy, chemical applications, and use of r esistant genotypes. (C) 2001 Academie des sciences/Editions scientifiques e t medicales Elsevier SAS.