الفهرس 
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Abstract
M.S. Thesis title: New Biological Trends in Extending Storage Life of Orang Fruit
By: Ahmed Nagah Akle - Environmental Studies and Research Institute (ESRI) – University of Sadat City
The present work was carried out in order to evaluate the ability of some rhizobial strains isolated from root nodules of wild legumes to act as biocontrol agent against the pathogenic fungi (Penicillium digitatum (Pers.:Fr.) Sacc (AUMC6258), Penicillium italicum Wehmer (AUMC 522) and Botrytis cinerea Pers (AUMC 11572) that cause green, blue and grey molds, respectively on Navel orange in vitro, to determine and select the best strains of rhizobia that have high antagonistic effect on green, blue and grey molds of Navel orange in vivo and to evaluate the effect of the best rhizobial antagonist on quality and store ability of orange fruits stored at room temperature (25±1°C) and cold storage (7±).
The work began by pathogenicity test to study ability of each one to of the three pathogenic fungi (P. digitatum, P. italicum and B. cinerea) to infect orange fruits at different incubation periods at room temperature (25±1°C). The Pathogenicity tests of the tested fungi on Navel orange fruits revealed that all the studied fungi were pathogenic and caused various degrees of fruit rot symptoms.
The antibiosis activity of the 11 rhizobial strains was screened against citrus postharvest pathogenic fungi P. digitatum, P.italicum and B. cinerea by dual-culture method. The results showed that four rhizobial strains NHBM10A, NHBM14, NHBM22B and NHBM24 have antibiosis activity against all the tested postharvest pathogenic fungi, while rhizobial strain NHBM16 has antibiosis activity against P.italicum and B. cinerea only.
The five rhizobial strains that had antibiosis activity were tested against citrus postharvest pathogenic fungi P. digitatum, P.italicum and B. cinerea (in vitro) to evaluate their ability in biologically control of the pathogenic fungi by agar well diffusion method. Almost all bacterial strains performed significant antifungal activity against the tested pathogens. Percentage of growth inhibition of the fungus treated with the bacterial strains changed from 50 to 100%. The most effective rhizobial strains on mycelial growth of the pathogenic fungi were the rhizobial bacteria Ensifer meliloti LMG 6133T strains NHBM14 and NHBM22B
The efficiency of the rhizobial strains to biologically control the citrus postharvest pathogenic fungi P. digitatum, P.italicum and B. cinerea on Navel orange (In vivo assays) was examined as follow: the orange fruits dipped into the suspension of the most potent two selected rhizobial strains (NHBM14) and (NHBM22B), then artificially wounded and inoculated with postharvest pathogenic fungi P. digitatum, P.italicum and B. cinerea, then stored at room temperature for 21 d. This test showed that the two selected rhizobial bacteria reduced decay on orange fruits surface in comparison to the control. The development of lesions (severity) of P. digitatum and P. italicum were significantly reduced in wounded orange fruits treated with rhizobial strains NHBM14 or NHBM22B, at all the periods of storage in comparison to the control treatment. However, the treatment with rhizobial strain NHBM14 or strain NHBM22B was not effective in reducing the development of lesions of B. cinerea at all storage periods in comparison to the control treatment.
The results of this study demonstrated for the first time that the rhizobial bacteria Ensifer meliloti LMG 6133T strains NHBM14 and NHBM22B could be developed as a biocontrol agent against the postharvest disease caused by P. digitatum, and P.italicum on citrus fruit.