Contemporary understanding of bacterial plant-diseases and their causal organisms

Abstract

At the turn of the century, the study of bacterial plant-diseases had already attracted much attention and provoked considerable discussion. Today it has acquired an impetus and a significance which warrant its recognition as an independent branch of science. After it had once been indisputably established that certain plant diseases are definitely caused by bacteria alone, it is not surprising that many diseases whose causes had previously remained unknown were also regarded as bacterial in origin. A most heterogeneous array of bacteria were then described as alleged causal organisms. Many of these earlier claims, however, have since been proved erroneous. At that time, for instance, it was said to be definitely established that Bacillus amtylobacter is the cause of damp-rot of potato and that Micrococcus populi is the causal organism of a disease affecting poplars in southern France. Passalacqua (78) described a leaf-disease of aloe in Palermo, attributing it to a sporeforming bacterium to which he gave the name Bacterium aloes. There was indeed a priori evidence for these early claims, since spore-forming bacteria were already definitely known in human diseases, such as tetanus and anthrax. It is well to regard all these early allegations with skepticism, since not one of the spore-forming bacteria, among which B. amylobacter is numbered, is conclusively known to be a true plant parasite. The cocci likewise play no role in plant pathology, in contrast with their importance in human and animal pathology. The alleged pathogenicity of Micrococcus populi has not been proved (83, 84) and the claims of Brussoff concerning Micrococcus ulmi as causing death of elm trees have already been refuted (104, 109, 126). This lack of evidence is significant, notwithstanding claims to the contrary, as those of Lendner (61), who attributes death of elms in the streets, gardens and parks of Geneva primarily to Micrococcus ulmi and Pseudomonas lignicola and only secondarily to the fungus Ceratostomella ulmi, which is the real cause. 405