الفهرس 
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Abstract
In Egypt, there is a growing increase in using herbicide to control weeds as an effective method alternative to conventional tillage practices. Application of pre-emergence herbicide might affect growth of soil-borne fungal pathogens in situ. Therefore, this study was carried out to investigate the effect of two pre-emergence herbicides i.e. pendimethalin and butralin at three different concentration (0.5X, 1X and 1.5X) on some soil borne fungus in vitro and in vivo causing stem blight of bean and on the diseases development. All experiments were conducted in the green house and laboratory of Plant Pathology Dept. College of Agriculture El-Minia University.
The obtained results could be summarized as follow:
• The isolate were identified as follow: R. solani three isolate, S. sclerotiorum (Lib) de Barry five isolates, M. phaseolina three isolates, and Fusarium sp, two isolate and one unknown isolate.
• All isolates showed damping off and stem blight. Symptoms of blight appeared first as water soaked lesion turn to brown, mycelial growth was observed on the lesion and the plants were finally killed.
• The highest values (60% of damping off), were recorded for R. solani (R1 isolate followed by M. phaseolina (M1 isolate), and then S. sclerotiorum (Ss1 isolate). The highest disease incidences of stem blight were 72.22, 66.65, and 61.11 for R. solani, M. phaseolina, S. sclerotiorum, respectively. However values of disease severity were 68.05, 59.60, and 56.94 for R. solani (R1), M. phaseolina (M1), S. sclerotiorum (Ss1), respectively. Other fungal isolates including Fusarium sp were showed weak virulence toward the tested cultivation were excluded from further studies.
• While decrease in Damping off ranged 46.67, 33.33for pendimethalin and 40.00, 33.33 for butralin a decrease in disease severity ranged between 39.58, 47.22, for pendimethalin and 40.28, 41.69, for butralin, depending on tested inoculum, compared with the control treatment, the tested isolates and used rates of both compounds values in damping off were 60.00, 530.33 and there were 63.89, 50.00 for severity depending on the tested isolates. Result in the second season showed the same trend of those obtained in the first season.
• Isolate of R. solani caused the highest damping off (%) infection 46.67 followed by M. phaseolina 46.67 and then S. sclerotiorum with 40.00 % infection where no herbicide were not applied. In soil amended with the herbicides there was as significant decrease in the percentage of damping off, at the concentration tested herbicide compared with the control (non-amended, infested soil).
• In case of treated pots with the herbicides, there was high significant in the severity of stem blight, at all tested concentrations for either pendimethalin or butralin, compared with the control treatment. The means of decrease severity at the highest concentration for example were 35.66 with R. solani, 32.77 with M. phaseolina and 28.56 with S. sclerotiorum (%) in case of pendimethalin. However means of decrease severity were 33.33, 30.75 and 29.33, in case of butralin.
• For example at the highest concentration of pendimethalin the mean damping off (%) was 40.18, 36.75 and 35.26 for R. solani, M. phaseolina, S. sclerotiorum, respectively.
• To investigate the effect of herbicide persistence (applied 60 days before sowing seeds in pre-inoculated soil with tested isolates) the results showed there was a significant decrease in the severity of stem blight, at all tested concentrations tested for either pendimethalin or butralin, compared with the control treatment.
• Incorporation of both herbicides at different rate had an adverse effect on the germination of sclerotia, carpogenicaly.
• A tested concentration of each of the two herbicides there was a significant decrease in the diameter of fungal colonies on the treated medium and the control (not amended with herbicide.
• At each concentration of both herbicides mean values of dry mycelium were significant compared with the control treatment (not amended medium). Generally at the highest concentration butralin induced a complete inhibition of the growing fungal isolates; while means value for pendimethalin at the same concentration were 170.0, 136.7, and 106.7 mg for R. solani, M. phaseolina, and S. sclerotiorum, respectively.
• Both compounds induced a highly significant decrease in the medium of sclerotia / plate).
• Both compounds at any each of three tested concentration significantly reduced mycleigenic germination of sclerotia originated from each of the two isolate and plated out in petri dishes contained Czapek Dox Agar media amended with both compounds with Pendimethalin the mean values for numbers of germinated sclerotia were 1.33 and 2.33 for Ss1, Ss2 respectively, when the compound was tested at 1X concentration while the same concentration of butralin gave mean value 0.33 and 1.00 for Ss1, Ss2 respectively. The mean value of control treatment was 3.00 and 3.00 for Ss1 and Ss2 respectively.
• Data indicated that the three fungal species R. solani, M. phaseolina, S. sclerotiorum varied in their utilization of pectin. R. solani and M. phaseolina grow vigorously in broth medium contained pectin, while S. sclerotiorum showed lower response of growth. Means values were 383.3, 400.0 and 2.38.3 for R. solani, M. phaseolina, S. sclerotiorum. Respectively. Incorporation of both herbicides into the medium induced high significant decrease in amount of mycelial development, compared with the treatment.
• Results indicated a variance among the three fungal species toward utilization of cellulose expressed as dry weight (mg) mean values of recorded dry weight were 403.3, 430.0 and 331.7 for R. solani, M. phaseolina and S. sclerotiorum, respectively, amended of culture medium with both pendimethalin and butralin at different rate significantly decreased the amount of growth for all tested fungal.
• The intermediate concentration (1X) the recorded pH values after 12 hrs. Incubation period, were 6.8, 6.65 and 6.45 for R. solani, M. phaseolina, S. sclerotiorum, in case of pendimethalin. In the same respected, there values at the same concentration and the incubation period were 7.0, 6.9 and 6.8 for R. solani, M. phaseolina, S. sclerotiorum, respectively. At the highest concentration of both compounds, there was a complete inhibition for the activity of PME with all tested isolates.
• Incorporation of pendimethalin or butralin into the culture medium significantly decreased the amount of TSP recorded, for example at (1X) concentration mean values of TSP were 0.098 , 0.141 and 0.083 in case of pendimethalin, while mean values were 0.090, 0.076 and 0.064 (g/l) for butralin at the same concentration for R. solani, M. phaseolina, S. sclerotiorum, respectively.
• The cultivated medium which supplement with the selected herbicides decreased the secretion of oxalic acid of both fungal isolates (Ss1, Ss2) compared with control as a metabolic product. This decrease in oxalic acid production was proportional to the increasing of herbicide concentration.
• The culture filtrate of both S. sclerotiorum, M. phaseolina induced wilting symptoms on cutting of bean seedling; however culture filtrate of R. solani did not show any wilt symptoms compared with the control, wilt symptoms produced by S. sclerotiorum isolates were much stronger than those caused by M. phaseolina. Incorporation of both herbicides (pendimethalin, butralin) into the culture medium resulted in decreasing of wilt symptom. The degree of wilt symptoms was gradually decreased as the concentration of herbicides.
• All tested concentrations caused an improvement in seedling height except those values exhibited with the highest concentration of butralin however the differences between the treatments and the control (infested and non-amended medium) were not significant.