Thesis (Ph.D)-Cairo University, 2025.

Bibliography: pages 107-139.

Crown gall caused by Agrobacterium tumefaciens (synonym Rhizobium radiobacter) is one of the most dangerous bacterial diseases affecting the production of fruit tree nurseries in Egypt and many countries of the world. A study of 55 bacterial isolates from the rhizosphere of stone fruit plants showed that ten isolates of 1-aminocyclopropane-1- carboxylic acid (ACC) deaminase-producing rhizobacteria were identified as Pseudomonas strains. Co-inoculating castor bean (Ricinus communis L.) and kalanchoe (Kalanchoe sp.) plants with A. tumefaciens and ACC-producing isolates of Pseudomonas vancouverensis reduced tumor formation in both plants. Also, the secondary metabolites of six of the 55 isolates inhibited the growth of A. tumefaciens, as indicated by the inhibition zone test. The results showed that those six isolates reduced the diameter and weight of tumors produced on kalanchoe and tomato (Solanum lycopersicum L.) plants. The six isolates were identified as Klebsiella, Pantoea (four isolates), and Enterobacter. GC-MS analysis of ethyl acetate (EtOAc) extracts of the metabolites of four selected isolates of the six isolates found that 4H-pyran-4-one, 2,3-dihydro-3,5-dihydroxy-6-methyl- is the major component in the metabolites of Klebsiella and Enterobacter and bis (2-ethylhexyl) phthalate in Pantoea metabolites. Meanwhile, LC-ESI-TOF-MS analysis found that hydroquinone and 4-methylcatechol are two of the major components in the EtOAc extracts of the metabolites of all four selected isolates. Meanwhile, two isolates (BPeK8 and BpeL6) that produce VOCs were selected from 55 isolates to evaluate their ability to inhibit the growth of A. tumefaciens and decrease crown gall disease. VOCs of BPeK8 and BPeL6 strongly affected the growth of A. tumefaciens. Scanning electron microscopic (SEM) analysis showed that the VOCs of the two isolates caused morphological abnormalities in A. tumefaciens cells. The results showed that VOCs produced by BPeK8 and BPeL6 can significantly decrease the pathogenicity of A. tumefaciens cells. The two isolates BPeK8 and BPeL6 were identified as Bacillus subtilis and Pseudomonas aeruginosa, respectively. GC-MS analysis identified the major peaks of VOCs produced by B. subtilis BPeK8 as dimethylamine, hydrazinecarboxamide, and acetoin. The major peaks of VOCs produced by P. aeruginosa BPeL6 were identified as oxalic acid, 1-butanol, 2-methyl-, (S)-, and cinnamaldehyde, (E)-. These results showed that many rhizobacteria species can control crown gall caused by A. tumefaciens by different mechanisms.

يعتبر مرض التدرن التاجي المتسبب عن بكتيريا tumefaciens Agrobacterium
من أخطر الأمراض البكتيرية التي تؤثر على إنتاج مشاتل الأشجار ال م ثمرة في مصر والعديد من دول العالم .أظهرت دراسة ل 55 عزلة بكتيرية من منطقة الريزوسفير لنباتات الفاكهة ذات النواة الحجرية أن عشر عزلات منتجة ل إنزيم 1 أمينوسايكلوبروبان 1 كربوكسيلك أسيد .
(ACC)تم التعرف عليها كعزلات من spp. Pseudomonas . أدى التلقيح المختلط لنبات الخروع ونبات الكالانشو إلى تقليل تكوين الأورام في كلا النباتين . كما وجد أن المستقلبات الثانوية ل 6 من العزلات قد عملت على تثبيط نمو tumefaciens A. وعزلتين منتجتان للمركبات العضوية المتطايرة

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