الفهرس 
DEDICATIONOnly 14 pages are availabe for public view
 |  | from | 74 |  |  |
| | | from | 74 | | |
Abstract
This investigation aimed to isolate and identify strains of the endophytic bacterial species Gluconacetobacter diazotrophicus from local sugarcane (cv. C9) cultivated in upper Egypt governorates (El-Menia, Assuit and Quena) and from sweet potato tissues (cv.Apies) grown at Assiut, and to compare their characteristics with those internationally reported (Bergey’s Manual of Systemic Bacteriology, 2005). Also, the abundance of this bacterial species in tissues of sugarcane and sweet potato as well as in the rhizosphere soil of Faculty of Agriculture Exptl. Farm were determined as indication of its establishment in soil and its endophytic occurrence in tissues of sugarcane and sweet potato. The serial dilution technique of sterilized macerated surface tissues (of sugarcane or sweet potato) in tubes of 5% sterile sucrose solution and inoculation on the selective LGI semisolid medium was followed. The positive tubes showing yellow subsurface pellicle were then serially sub cultured for 5-7 times on LGI semisolid medium for enrichment and purification of the isolates before streaking on plates of the acid LGI agar medium to obtain separated colonies which were then transferred to tubes of the LGI semisolid medium as pure isolates. The identification and characterization of the Isolated Strains were Based on the Following: A. Phenotypic and biochemical tests: Cell morphology and Gram reaction, motility, catalase reaction, use of the following sugars and organic substances as sole C source for growth and acid production: sucrose at 30% concentration, glucose, arabinose, maltose, mannitol, Na- citrate, malic acid and ethanol at 0.5- 1.0% concentration. B. Colony characteristics of the isolated strains formed on plates of the following media: LGI agar, potato sucrose (PS), ethanol-CaCO3 and glucose-CaCO3 agar (GYC). C. Catalase reaction, solubilization of phosphate, hydrolysis of starch and reduction of nitrate. D. N2-fixing activity, determined by the ARA and by determining the amounts of total nitrogen fixed / g sucrose consumed from, the LGI liquid medium after growing the strains for 7 days. The results obtained from these tests indicated that the isolated strains (14 strains from sugarcane, and 5 strains from sweet potato) belong to the species Gluconacetobacter diazotrophicus. This was also confirmed by their N2-fixing activity determined by the micro-kjeldahl method that was found to range from 12.2 to 17.6 mg N/ g sucrose consumed in case of the strains isolated from sugarcane tissues, and from 11.6 to 13.2 mg N/ g sucrose consumed in case of sweet potato isolated strains. The enumeration of Gluconacetobacter diazotrophicus in the rhizosphere soil of Assiut Exptl. Station and in tissues of sugarcane and sweet potato was determined by the MPN technique using LGI semisolid and MaCradye statistical table. The recorded numbers of endophytic Gluconacetobacter diazotrophicus in sugarcane root tissues were from 0.3 to 3.0 × 106 /g, and in stem buds from 0.2 to 4.0 × 105 /g; and in roots of sweet potato ranged from 0.5 to 9.2 × 104 /g and from 5.6 to 11 × 105 /g of sweet potato tubers. Whereas, the numbers of rhizospheric Gluconacetobacter diazotrophicus were slightly lower than those endophytic and ranged in sugarcane rhizosphere from 2.6 to 16 × 105/ g soil and in sweet potato rhizosphere from 2.1 to 9.2 × 104/g soil. These results indicate the presence of high numbers of this bacterial species in roots tissues of both sugarcane and sweet potato as well as tuber tissues of sweet potato. Also, the obtained enumeration results indicate the establishment and endophytic occurrence of this bacterial species in tissues of local sugarcane and sweet potato grown in upper Egypt, as well as its occurrence also in the rhizosphere soil in spite of the harsh environmental conditions in Assiut area (dry and hot weather) and where heavy nitrogen fertilization is added to the plants.