In greenhouse experiment, three strains of effective plant growth-promoting rhizobacteria (PGPR), Pseudomonas fluorescens, Paenibacillus polymyxa and Azospirillum lipoferum were evaluated for biological control of Fusarium wilt of pepper caused by Fusarium oxysporum f. sp. lycopersici. Visual inspections of root colonization by
water-agar tubes technique indicated that, all the tested bacteria were able to colonize pepper root systems, whereas in separated greenhouse experiment, inoculation of bacteria by the over head-soil method caused higher colonization of the tested PGPR than root soaking technique either in the rhizosphere or in the root material. Significant decrease of dehydrogenase and phosphatase activity was observed when soil was infested with F oxysporum. Maximum values of dehydrogenase activity were obtained by using over head-soil technique with triple inoculation while, dual inoculation with P. polymyxa and
Az. lipoferum gave the maximum records of phosphatase activity. The percentage of disease incidence caused by F. oxysporum of plants after treatment with PGPR as biocontrol agents were lower than those infected with pathogen only. Moreover, Ps. fluorescens or P. polymyxa singularly or in mixture were the best strains for controlling of Fusarium wilt of pepper since they recorded the lowest percentage of disease incidence and the maximum percentage of biocontrol efficacy. Also, inoculation of the antagonistic bacteria by over head-soil method gave lower percentage disease incidence and higher biocontrol efficacy than root-soaking technique. Data also indicated that peroxidase and
polyphenol oxidase increased in plants those infected with the pathogen singularly than healthy plants those no infestation. Also, remarkable increase was observed in peroxidase and polyphenol oxidase in the plants inoculated with Ps. fluorescens either individually or in combination with the other PGPR. Data also demonstrated that, soil infestation with F. oxysporum significantly decreased root size, root dry weight, plant height and shoot dry weight of pepper as compared with control (plants not infested with F. oxysporum). Growth characters were significantly increased in the infested plants those inoculated
with PGPR individually or the mixture of them, especially Az. lipoferum and P. polymyxa.
------------
Key words: biocontrol, Pseudomonas fluorescens, Paenibacillus polymyxa, Azospirillumlipoferum, soil enzymes, Fusarium wilt, disease incidence |
