الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Rhizobacteria are a diverse group of soil microbes that have multiple activities toward plant growth promotion. They have potential for usage inagriculture and can result in higher crop yields for a number of different crops. Also they are expected to replace the chemical fertilizers, pesticides and artificial growth regulators which have numerous side- effects to sustainable agriculture. Two of the most studied PGPR are Rhizobium andSerratia. They are known for their ability to synthesize plant hormones in different concentrations. Indoles, mainly indole-3-acetic acid, which alter plants metabolism and morphology leading to better absorption of mineralsand water, accordingly larger and healthier plants.
In our study, collection and isolation of Rhizobium and Serratia isolates. They were tested for their ability to produce IAA and were identified depending on morphological and biochemical consideration. Primary screening based on IAA production concentration in the presence of L-tryptophan indicate that two isolates from eighteen isolates, were producing high IAA level and the highest level observed in isolate NRC- R2 1079 μg/ml and ACGEB-S2 357 μg/ml.
Two isolates that considered as a highest IAA producers identified molecularly using (16SrRNA) with 27F and 1492R primers. A Blastn search in GenBank revealed that one of the Rhizobium isolates (NRC-R2) shared 95% sequence similarity with Rhizobium sp., while the Serratia isolate (ACGEB)-S2) was 99.5% similar to Serratia sp. These two isolates were subjected to genetic improvement in order to produce a high level of IAA using UV radiation.
Rhizobium (NRC-R2) and Serratia (ACGEB-S2) were exposed for UV radiation for different time intervals (15 to 240 sec.) as a preliminary experiment. After that, UV exposure was conducted for 120 sec. with Serratia (ACGEB-S2) and 30 sec. with Rhizobium (NRC-R2). Eight mutants of each were taken randomly and screened for indole productionin
presence of L-tryptophan. Results showed that the best mutant production was S2 mutant-7 mutant which produce 515.59 μg/ml of IAA.