الفهرس 
INTRODUCTION
ActinomycetesOnly 14 pages are availabe for public view
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Abstract
Eighteen actinomycete colonies with different morphotypes were isolated by direct plating of the soil of Experimental Farm of Faculty of Agriculture, Assiut university, Egypt, planted with wheat, faba bean and clover. The majority of the isolates grew within 7-10 days and sporulation was noticed after 12-14 days. The strains were purified by visual, microscopic and cultivation methods. The results of microscopic features showed that, nine isolates have Spiral chains of spores with different morphology.
The nine phosphate solubilizing actinomycete isolates were identified on the basis of colony characteristics, microscopic observation and biochemical test. Spore chain arrangements observed using research microscope and scanning electron microscope showed that of all the isolates bear spore spiral chains. The colony surface was cottony and colony colour ranging from whitish, yellowish white and grey. All actinomycete isolates were able to hydrolysis starch, casein, urea and use glucose fructose, sucrose, lactose, mannitol as sole carbon sources. In accordance with the aerial mycelium, spiral spore chain and colony color established in Bergey’s Manual of Determinative Bacteriology, 9th edition (Daltimor 1994), the nine isolates could be grouped under the genus Streptomyces.This investigation included several laboratory and two pot experiments for studying the following specific objectives: 1. Test the ability of actinomycete isolates to solubilizeinorganic phosphates.2.Test the ability of actinomycete isolates to produce organic substances in their cultures, which can chelate iron (or other polyvalent mineral ions) from soil.3.Test the effect of inoculation with actinomycete isolates on wheat plants in sandy calcareous soil and choose the best two actinomycete isolates.4.Study the effect of inoculation with actinomycete isolates (the best stains) on P-uptake and growth of wheat plants in sandy calcareous soil under different P-levels.Screening of actinomycete isolates for phosphate solubilization:The purified actinomycete isolates were screened for the solubilization of inorganic phosphates on Pikovskaya’s agar medium. Out of the 18 isolates, 9 (50%) showed an ability to solubilize inorganic phosphates based on inducing clear zones around their colonies. The phosphate solubilization indexes of the strains A1, A2, A3, A4, A5, A7, A8, A10 and A18 were 3.40, 2.40, 2.57, 4.50, 3.10, 1.57, 2.10, 3.83 and 1.83, respectively. The highest phosphate solubilization index was recorded by the strain A4 and the lowest by the strain A7.
The isolates were further studied for ability to solubilize phosphorus from insoluble phosphate in Pikovskaya,s liquid medium containing tricalcium phosphate. Amounts of phosphorus solubilized by the actinomycete isolates A1, A2, A3, A4, A5, A7, A8, A10 and A18 respectively were: 52, 45, 46, 78, 32, 37, 36, 55 and 45 mg/100 ml culture, respectively. The highest amount of P solubilized (78 mg/100 ml culture) was recorded for actinomycete isolate A4, which also showed the highest phosphate solubilization index (4.5) and the lowest pH (4.00) in a 10-day old culture. The results also showed that the lowest amount of P solubilized was recorded by the actinomycete isolate A5 (32 mg/100 ml culture). This indicates that the organic acids produced from fermentation of sugars in the medium by the actinomycete isolates may be the main cause of solubilization.Actinomycete production of organic chelating substances: The ability of actinomycete isolates to produce organic substances in their cultures, which can chelate iron (or other polyvalent mineral ions) from soil, was tested in laboratory experiment. The results show that all actinomycete isolates produced in their cultures organic substances that chelated iron from the soil. The extracted amounts of iron by the actinomycete cultures were 1.00, 0.93, 0.98, 1.18, 0.86, 0.89, 0.92, 1.07 and 0.95 ppm for the strains A1, A2, A3, A4, A5, A7, A8, A10 and A18, compared with 0.36 and 1.26 ppm extracted by starch casein liquid medium and DTPA. These results show the difference in amounts of extracted Fe by actinomycete cultures, being highest by strain A4 and lowest by strain A5 culture. The data also show that the iron extracted by A4 culture (1.18 ppm) was less than that extracted by DTPA (1.26).
Growth curves for phosphate solubilizing rate of the actinomycete isolates A4 and A10:
The growth curves, drawn for phosphate solubilizing rate, of the actinomycete isolates A4 and A10, (grown on Pikovskaya,s liquid medium containing tricalcium phosphate) show that the initial solubilize inorganic phosphate by the both actinomycete isolates beginning after 24 hours and Phosphate solubilizing rate increased exponentially with time. Maximum Phosphate solubilizing rate was recorded after 10 days for both isolates and the isolate A4 was recorded higher phosphate solubilizing rate than the isolate A10.
Response of wheat to inoculation with actinomycete isolates:
The pot experiment was carried out in season 2016/2017 to test the efficiency of actinomycete isolates on growth of wheat in sandy calcareous soil. The obtained results show that all actinomycete strains caused significant increase (p = 0.05) in plant height and shoot fresh weight except for strain A3, but non-significant increase in root fresh weight. Significant increase in shoot dry weight was recorded by inoculation with strain A3, A4 and A10. Inoculation with strains A1, A4, A5 and A8 caused Significant increase in root dry weight compared with uninoculated control. It should be noticed that the isolates A4 and A10 induced the highest stimulative effects on growth parameters of wheat. The obtained results show that in general the inoculation with actinomycete strains increase the phosphorus uptake by wheat plant. Significant increase in phosphorus uptake in case of inoculation with actinomycete strains A1, A4, A8 and A10, compared with control.
Effects of inoculation with actinomycete isolates A4 and A10 on growth and p-uptake by wheat under different levels of P-fertilization:
Data obtained on the main effects of inoculation with actinomycete isolates A4 and A10 and different levels of P-fertilization (25, 50 and 100 % from recommended dose of phosphorous, RDP) show that inoculating the wheat with A4 and A10 actinomycete isolates caused significant increases (p = 0.05) in the plant height, root and shoot dry weights and P-uptake by the shoots of wheat plant compared to the uninoculated control plants. The A4 actinomycete isolates showed higher promotive effects on plant height, root and shoot dry weights and P- uptake by the shoots than those shown by the A10 actinomycete isolate. Inoculation with the A4 actinomycete isolate resulted in an increase in P- uptake by plant shoots of 297.97 %, of the uninoculated control. Growth responses and P-uptake of wheat plants to P fertilization show that only, the P fertilization at a level of 100 % of the recommended dose (RDP) had a significant influence on plant height, root and shoot dry weights and P uptake by the shoots and roots.
The interaction effects of the inoculation with the A4 and A10 actinomycete isolates and the P fertilization show that a promotive effect of inoculating the A4 actinomycete isolate on the plant height, root and shoot dry weights and P uptake by plant shoots was more obvious at the P level 50 % of RDP. However, at the higher level of P fertilization (100 % RDP), the promotive effect of inoculation decreased. In other words, the best promotion effect from inoculation with A4 actinomycetes isolate was obtained at P- fertilization level 50 % of RDP. The increases in the plant height, shoot and root dry weights and P uptake by plant shoots were: 37.39, 465.45, 289.65, and 233.6 % respectively, of the uninoculated control fertilized with 100 % of RDP. These results indicate the importance of plant inoculation with phosphate solubilizing microbes, such as A4 actinomycetes isolate for decreasing the application of p-fertilizers in agriculture.