This research was carried out to study the effect of mycorrhizai inoculation and/or phosphatic fertilization on damping-off and root-rot diseases in sour orange. Obtained data showed that Fusarium oxysporum was the most destructive soil pathogen causing damping-off and root-rot of sour orange. Percentage of disease severity increased by the increasing of inoculum potential Soil infestation with F. oxysporum alone caused the highest percentage of pre- & post¬emergence damping-off and root-rot diseases. Mycorrhizai inoculation significant^ decreased the percentage of disease severity caused by F. oxysporum.
Moreover, the highest counts of total microbial flora were obtained from mycorrhizai inoculation alone. While, the highest counts of actinomycetes were resulted from mycorrhizai inoculation in combination with super-P. On the other hand, the lowest counts of total microbial flora and actinomycetes were resulted from soil infestation with F. oxysporum either alone or in combination with super-P. Soil inoculation with Glomus macrocarpum + F. oxysporum in combination with super-P led to decrease the populations of soil fungi.
Also, data showed that the treatment including G. macrocarpum + F. oxysporum gave the highest value of total phenols and lowest value of free phenols. The highest values of total carbohydrates were obtained from mycorrhizai inoculation combined with F. oxysporum whereas, the lowest ones were observed in the treatments including F, oxysporum either alone or in combination with super-P.
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