الفهرس 
ACKNOWLEDGEMENT
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Abstract
The first part of this investigation concerned with isolation and identification of vitamin producing microorganisms from six plants. The plants were collected from different localities (Abnub, El-Badari, El-Fateh, Manfalut, Assiut and El-Qusiya) in Assiut Governorate, Upper Egypt. The second part of this study focused on screening for highly riboflavin and β-carotene microbial producers and improvement of medium components for high riboflavin and β-carotene production. The current results could be summarized in the following points:- 1- Ninety seven species and two varieties belonging to 33 genera of fungi were isolated during the current investigation. Alternaria, Aspergillus, Cladosporium, Fusarium, Penicillium and Rhizopus were the most common genera recoverd from all plants. However, Aspergillus flavus, A. fumigatus, A. niger, A. terreus, Cladosporium herbarum, Fusarium graminearum, F. solani, Penicillium chrysogenum and Rhizopus stolonifer were the most dominant species isolated from all plants in this investigation.The total isolates of yeasts were 134 isolates and the total isolates of bacteria were 193 isolates isolated from all plants. 2- Seventy one species and one variety belonging to 28 genera of fungi were recovered from rhizosphere plants. Lemon plants recorded the highest total count contributing 25.36% of total rhizosphere fungi. The most isolated genera and species from six rhizosphere plants were Aspergillus (A. niger and A. terreus), Fusarium (F. solani), Penicillium (P. chrysogenum) and Rhizopus (R. stolonifer) matching 44.23%, 22.7%, 8.31% and 0.89% of total rhizosphere fungi, respectively. Twenty five yeast isolates were recovered from rhizosphere plants and the highest total count (36.07%) was isolated from zucchini plants however, twenty nine bacterial isolates were isolated from rhizosphere plants and the highest total count was recorded from banana plants (20.37%).