الفهرس 
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Abstract
Actinomycetes have been known to be one of the multifunctional microorganisms in particularly producing compounds having antagonistic activities against different pathogens. This study aimed at evaluating the antagonistic efficiency of some Streptomyces isolates isolated from an Egyptian soil against the root-knot nematodes (Meloidogyne incognita). Seven soil samples were collected from different regions of Sharkia Governorate, Egypt, and actinomycetes were isolated, purified and identified up to genus. The ability of chitinase production via streptomycete isolates were tested, and the highest efficient isolates were identified up to species based on the biological keys of ISP system followed by molecular identification among determining the nucleotide sequences of their 16S rRNA genes and finally documented in GenBank. The nematicidal activities of the streptomycete strains were tested against root-knot nematodes (M. incognita) in vitro and in vivo. Phylogentic trees showed that the five streptomycetes were classified as strains of Streptomyces levis (ST01), Streptomyces enissocaesilis (ST07), Streptomyces plicatus (ST10), Streptomyces rochei (ST15) and Streptomyces sparsus (ST16) and documented in GenBank under the accession numbers of LC732277.1, LC732278.1, LC732279.1, LC732280.1 and LC732281.1, respectively. Results of nematocidial activities of the five streptomycetes agaist J2 of M. incognita showed that death rate of J2 was higher at concentration of 20 % than at 10 and 5 % and mortality rates grew steadily as exposure duration was extended to 72 hour. Hatching of eggs was inhibited by an average of 86.8, 85.4, 78.9, 77.8 and 68.1 % for ST15, ST10, ST16, ST01 and ST07, respectively. The longest root length (20.1 cm) was attained by the ST15 strain followed by the ST10 strain (17.4 cm) compared to control. Most assessed Streptomyces strains had a detrimental impact on nematode counts, soil population, galls, egg masses and the number of egg/egg masses. Antifungal activity of Streptomyces isolates was examined. from 24 isolates only 15 isolates exhibited inhibitory activity against tested fungi. Out of these 15 isolates, 12 isolates showed activity against Fusarium oxysporum, 8 against Rizoctonia solani, 14 against Pythium ultimum, 6 against Scelortium spp., 11 against Verticillium spp. and 8 against Phytophtora parasitica. Indole acetic acid (IAA) was produced by all the assessed active isolates with variable rates ranging from 7.56 µg/mL to 59.12 µg/mL. Supreme production of IAA was attained by the strains ST15. Almost all strains increased the roots dry weight but the significant weight increase over the range of 67-217%. The lowest counts of J2 in soil (288) was achieved by strains ST15 followed by strain ST10 with population (309) compared to nematode infected soil (3787). As a conclusion, all Streptomyces strains showed variations in their impacts on the root knot nematode female fecundity as indicated by the counts of egg/egg masses and reduced the number of eggs within range between 17-55 %. Comparing to control (79.00) all streptomycete strains significantly reduced the counts of egg mass per gram root. A great reduction of egg masse was realized by strain ST15 (37.00) followed by Strain ST10 (40.00). The total chlorophyll in Streptomyces-treated eggplants was 3.5-5.1 mg/g F.W. compared to infected control 1.6, and carotenoids content in Streptomyces-treated plants ranged from 0.38-0.65 mg/g F.W. compared to infected control was 0.27 mg/g F.W. The treatment of eggplant samples with ST15 significantly enhanced the pigments’ content whenever infested samples mitigated the nematode population. The level of MDA and H2O2 was elevated in nematode-infested eggplants by 28-33% in Streptomyces-treated eggplant samples compared to untreated and uninfected control plants. The activity of antioxidant enzymes in mitigating the nematode stress on eggplant. Generally, the activities of all antioxidant enzymes (SOD, Pyx, and CAT) were at a regular rate in Streptomyces-treated samples, especially ST15, followed by ST10 and ST16 compared to non-infested control. The enzyme was in the highest activity 6 U/g protein, which upregulated with 116-191% over St-treated eggplant samples, where ST15, ST10, and ST16 maintained the SOD level in regular limit.