الفهرس 
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Abstract
The aim of this present study is to assess the effect of two commonly used fungicides as seed dressing on clover, peanut and faba bean rhizobia and to identify potential fungicide resistant strains of rhizobia that can be used as inoculant strains.
In the present study, one hundred and three rhizobial isolates were obtained from root nodules of clover, faba bean, and peanut collected from different ecological areas of Egypt.
The effects of the two fungicides (Vitavax and Rizolex) on rhizobial isolates were found to depend on the fungicide type and concentration as well as on the rhizobial isolate.
The fungicides inhibited the growth of most rhizobial isolates particularly at higher fungicide concentrations. However, some isolates were found to resist the high concentrations of the fungicides.
1. The clover rhizobial isolates differed in their tolerance to the various concentrations of the fungicides in the media. The retardation was higher at higher fungicides concentrations. Some isolates showed distinct tolerance to the fungicides. None of the concentrations 750 and 1250 ppm of the two fungicides was capable to eliminate the clover isolate growth totally.
2. The clover rhizobial isolates TO1 and TO2 were the most resistant isolates. The clover rhizobial isolate TO1 had only 14% of retardation growth at the concentration of 1250 ppm of Vitavax, and 28% with the same concentration of Rizolex.
3. The two fungicides at concentration of 1250 ppm had toxic effects on all isolates isolated from clover.
4. Less toxic effects were observed with fungicides concentrations 250 and 750 ppm on clover isolates.
5. The fungicides Vitavax and Rizolex at 1250 ppm had toxic effects toward all isolates of faba bean rhizobia.
6. Faba bean isolate TA2 was the highest resistant isolate (among its group) to fungicides, where this isolate had 57% retardation at 1250 ppm of Vitavax respectively, and 55% at 1250 ppm of Rizolex.
7. Faba bean isolates TA17 and BA4 were very sensitive to the high fungicide concentration as it gave 87% and 91% growth retardation with Vitavax and Rizolex respectively.
8. Peanut isolates P2, P10 and P11 were more sensitive to Vitavax than Rizolex at all used fungicide concentrations. The 750 ppm fungicide concentration gave between 45 to 76 % retardation with Vitavax and 31 and 76 % with Rizolex.
9. Two peanut isolates (Sa1, Sa3) were resistant to the highest concentration of Vitavax, however, isolates (He10, Sa1, SaK7) were not resistant to the Rizolex at the same concentration.
10. The most resistant ten rhizobial isolates to the fungicides three from clover (TA2, TO2 and TO1), three from faba bean (TO12, TO14 and ME 20) and four from peanut (8, 22, 34 and 51) were subjected to higher concentrations of both fungicides up to 2000ppm. The growth retardation was proportional to the increase in fungicide concentration. The negative effect of with Rizolex at higher concentration 2000 ppm was more pronounced than Vitavax.
11. Isolate TO12 from Vicia faba was the most resistant to Rizolex.
12. All peanut isolates growth values were reduced sharply after 10 days of incubation particularly at fungicide concentration of 2000 ppm of Vitavax or Rizolex.
13. The peanut isolate No. 51 was more sensitive to Rizolex or Vitavax than isolates 8, 22 and 34 which tolerated to the two fungicides.
14. The two most tolerant strains/isolates (clover rhizobia isolate TA2 and peanut isolate 8) were assessed in their capacity to degrade Vitavax and Rizolex.
15. Using HPLC analyses revealed that the control sample showed specific peak indicating the Vitavax presence in the medium. The specific peak was constant in all samples of the control at different time intervals. With the strain TA2 the specific peak of the Vitavax fungicides started to reduce generally as the incubation time goes on.
16. The Vitavax fungicide did not degrade completely until the 10 days of incubation. Two new intermediates were released into the medium indicating the degradation of the tested fungicide by rhizobia.
17. Thiram (the active ingredient of Rizolex fungicide) was degraded by peanut rhizobial isolate NO 8. In 48 hrs 45% of this compound was degraded.
18. The effect of the applications of these two fungicides on rhizobial inoculants performance was studied. The inoculation with rhizobia has almost doubled the plant dry weight and increased the nodules numbers and weight, The Vitavax application combined with rhizobial inoculation has significantly reduced the plant dry weight.
19. The rhizobial inoculation combined with Rizolex treatment has resulted in significant increase in plant dry weight, nodule weight and number as well as plant nitrogen content as compared with any other treatment.