Mutational studies on virulence in Erwinia atroseptica

Plant pathology

Duncan, James Moffat

University:University of Glasgow

关键词: Plant pathology;   

Others  :  http://theses.gla.ac.uk/73127/1/10647504.pdf

来源: University of Glasgow

【 摘 要 】

The roles of various physiological systems in the ability of Erwinia atroseptica to cause soft rets of potato tuber tissue were investigated by studying isolates, mutant for these different characters. One of these characters was pectic enzyme production where it was shown that the only detectable pectic enzyme produced both in vitro and in vivo was endo-polygalacturonate trans-eliminase. Mutants which were selected out on their inability to liquefy pectate gels proved to be abnormal for the production of this enzyme as well as having greatly reduced virulence. Culture filtrates of these different mutants caused maceration and browning of potato tissue in amounts corresponding approximately to the levels of enzyme activity they contained. Different types of soft rots were observed for isolates with different colony appearance on glucose minimal medium agar. It was possible to select from one single colony isolate of one colony type, creamy, mutants which had the appearance of the other colony type, diffuse. These isolates caused soft rots characteristic of the other diffuse isolates. Various diffuse isolates differed from one another, and the creamy isolates, in different characteristics according to the particular isolate under study. However, they always differed from the creamy isolates in the type of soft not they caused, the levels of endo-P.G.T.E. produced in vitro, and their colonial morphology on glucose containing media. Changes in ph occurring in infected host tissue might explain the differences in the soft rots produced by creamy and diffuse isolates. The higher pllo found on infection with isolats my result in the prevention of the browning infected host tissue by reversing the effect of the through the action of bacterial dehydrogeness. Differences found in the ph of infected tissues did not occur in vitro. Other studies on colonial morphology produced evidence to suggest that the metabolism of pectic substrances and their breakdown products by the bacterium may be associated with its metabolism of galactose and lactose. However, this dees not appear to be directly related to the ability of an isolate to cause soft rots. Similarly evidence is presented to show that the motility and the production of proteolytic enzyme by this organism do not appear to be directly involved in the production of disease symptoms by an isolate. It would appear that the characters most closely associated with an isolate's virulence are its ability to produce endo-P.G.T.E. and its colonial morphology, which is possibly related to an ability to raise the ph of the hot tissue being infected.