The role of pectinase enzyme in the development of soft rot caused by Pseudomonas fluorescens in the purple variety of onions (Allium cepa)


Simbo Aboaba

Pectic enzyme production was induced in vitro by culturing the pathogen (P flourescens) in minimal salt medium containing citrus pectin as the only carbon source and in vivo by inoculating the pathogen into healthy onion bulbs. The spent broth and onion rot extract were obtained and enzyme detection was done using viscometric method and cup plate assay. The crude enzyme was partially purified by precipitating with ammonium sulphate and dialyzed against water at 4o C for 24 h before use. The activity of the purified enzyme was determined based on the macerating ability on Onion and Potato discs and later by estimation of reducing sugars (galacturonic acid) level. The type of cleavage reaction of the enzyme was determined using the thiobarbituric acid reaction and the presence of antimicrobial substance in the rot tissue was also investigated. The pathogen produced a hydrolytic polygalacturonase in vitro and in vivo. The purified enzyme showed appreciable activity with all the assay methods used. Activity was highest at pH 5 in the culture filtrate sample and at pH 4 in the rot extract. Maceration was observed in potato and onion discs. The detection of increasing concentration of polyphenols in the rot tissue during rot development demonstrated the plant’s response to the pathogen.

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