Bacterial stem rot of dieffenbachia in Egypt

This work was carried out to isolate and identify the causal organism. Studies included also the host range of the organism. The causal organism was isolated from naturally infected stems of Dieffenbachia picta showing typical rot symptoms. All plants used for isolation were grown in the greenhouse of Faculty of Agriculture in Menia. Four isolates of motile, rod shaped, Gram-negative bacteria were isolated from soft rotted areas. The disease was induced by artificial inoculation of healthy stems of Dieffenbachia with any of these isolates. The bacterial isolates differed in their virulence. Host range studies revealed that the pathogen is able to produce soft rot on fruits or stems of eggplant, tomato, pepper, squash, potato tubers, carrot, turnip and table beet roots. Inoculated stems of chrysanthemum and potato became soft and the softened areas spread rapidly to cause wilting and death of affected plants. Stems of maize and cowpea show no symptoms and remain unaffected. Diagnostic tests and electron microscopic examination suggested that the pathogen as a new species for which the name Erwinia dieffenbachii is proposed. This is the first report on the occurrence of E. dieffenbachii in Egypt

Pectolytic and cellulolytic activity of enzymes secreted by erwinia dieffenbachia, causing stem soft rot on dieffenbachia plants

Fourteen isolates of Erwinia dieffenbachia were isolated from dieffenbachia stem rot, four of them were rated as highly, moderately and weakly virulent and were active in secreting pectin methylesterase, polygalacturonase and cellulase enzymes in vivo and in vitro. They varied in their enzyme production. The highly virulent isolate produced in the culture filtrates 3-5 times higher PME, PG and cellulase activities than the low virulent one. Dieffenbachia stems inoculated with any of the tested isolates showed higher activity of such enzymes than healthy stems. A correlation between the PME, PG and cellulase activities and the pathogenicity of the tested pathogen isolates was detected

Response of cactus and nicotiana glutinosa leaves to infection by soft rot bacteria

All tested isolates of E. carotovora subsp. carotovora were able to induce hyperseitsitive reactioin [HR] in leaves of cactus and Nicotiana glutinosa plants. Unwashed cells of the less virulent isolate Et of the subsp. carotovora induced HR in cactus leaves after a longer period. Moreover, unwashed cells of E.carotovora subsp. atroseptica isolate Epo2 induced the weakest reaction. When cactus leaves were injected with washed cells of the same isolates the latent period decreased to 3 days and the browning of lesion colour occurred faster, at the 10th day, the more virulent isolates induced HR within a shorter period, whereas with the less virulent isolates, the time required for such reaction was not affected or even increased. When N.glutinosa leaves were injected with unwashed cells of highly [EP2] and moderately [Et] virulent isolates of subsp. carotovora the HR become visible after a short period. This time period increased when the washed cells of those two isolates [EP2 and Et] were used for injection. In contrast E.c.subsp. atroseptica did not induce HR in N.glutinosa leaves. Cell-free culture filtrates prepared of any tested bacterial isolates of both subsp. caused in leaves of cactus and N.glutinosa a HR moderate in intensity and after a shortest time period

Extracellular polysaccharides and agglutination to soft rot bacteria

Erwinia caratovora subsp. carotovora and subsp. atroseptica produced viscous substances in 5% sucrose culture medium. The chemical analysis of alcohol-insoluble precipitate was positive for carbohydrate, negative for protein and consist of xylose and galactose and sometimes of galactose only. The subspecies carotovora produced free-EPS two-three-fold more than the subsp. atroseptica. Exopolysaccharides of the subsp. carotovora was found to cause reversible wilting of tomato cuttings. Moreover, the unwashed cells induced soft rot for potato and pepper fruits two-five fold more than the washed ones, indicating the important role of EPS in pathogenesis. The highest concentration [600 micro, g/ml]of the three buffered fractions [A,B and C] prepared from corn grains strongly agglutinated the bacterial cells of E.carotovora subsp. carotovora and subsp. atroseptica. At the lower concentrations [150 micro.g/ml] of fractions A and C, the washed cells of both subsp. were agglutinated, whereas the unwashed were not. These results indicate the necessity of EPS for full virulence of subsp. carotovora

Effect of some plant extracts on growth and enzyme activities of soft rot bacteria

The water - soluble extracts prepared from com foliage, soybean seeds, cotton foliage and anise seeds inhibited growth of soft rot bacteria. At higher concentrations, 78 mg, 32mg, 80mg and 67 mg dry weight / ml of corn, soybean, cotton and anise extracts respectively the bacterial cells were killed. Moreover, isolated varied greatly in their sensitivity to the substances present in soybean and anise extracts. When the crude extract of soybean seeds was added to the growth medium of E. carotovora subsp. carotovora its population was substantially checked and consequently its total pectolytic and cellulolytic enzyme activities decreased, but not as sharp as its growth. Thus, when the activity was calculated on basis of a constant number of bacterial cells [108 / ml], it appeared that the extract enhanced these enzyme activities. In addition polyphenoloxidase activity of E. carotovora subsp. carotovora was affected by the soybean seed extract almost similarly as in case of pectolytic and cellulolytic enzymes. Contrary to the results obtained with the above enzymes, soybean seed extract supplemented to the growth medium of E.C. subsp. carotovora isolates either strongly or completly inhibited their peroxidase activity

Bacterial leaf blight of cowpea in Egypt: 1 Causal organism and factors affecting its growth

Naturally infected plants showed leaf blight and stem canker symptoms. Leaf inoculated plants exhibited irregular reddish brown blotches followed by leaf wilting, while stem or pod inoculated ones develop either cankers or brownish water-soaked spots, respectively, at the sites of inoculation. Diagnostic tests suggested the pathogen to be Xanthomonas campestris p.v. vignicola. Varietal response test showed that isolate varied as regards the severity of symptoms they initiated in a given variety of bean or cowpea. Host range studies revealed that the pathogen is able to initiate a hypersensitive reaction in tobacco, tomato, squash, braod bean and common apricot. Trials on antibacterial compounds revealed that Terramycin, Penicillin, Chloramphenicol, Streptomycin and Erythromycin as well as Marfazin and formaldehyde had the most pronounced inhibitory effect on growth of the bacterial isolates tested