الفهرس 
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Abstract
This thesis was about sugar beet diseases caused by several soil born fungi. Stand loss occur when these fungi cause root rot, pre- and post- emergence damping- off, crown rot and root rot. Results obtained could be summarized in following points. Field survey was conducted through 2005 and 2006 growing seasons to determine the most prevalence and dissemination of fungal infection at El-Sharkia and El-Dakahlia governorates. Four locations with different soil types at each governorate where chosen to survey sugar beet fields for fungal root rot infection. Inspection of disease symptoms was done through seedling to mature plant stages. The highest percentages of disease incidence (24, 23 and 22%) were recorded in Awlad Saker, Kafr Saker and Hesania counties at Sharkia governorate; respectively. The highest percentages of disease incidence 25% and 23% were recorded in Belkas and senbelawin counties at Dakahlia governorate; respectively. In laboratory tests, all Trichoderma species showed strong antagonistic effect in suppression of fungal pathogen under study more than the bacterial antagonists. T. viride and T. hamatum were ranked the second in the antagonistic effect after T. harzianum and in some cases it was similar it while P. fluorescens showed better antagonistic effect more than B. subtilis. Garlic, Onion, Clove and Artemisia extracts were the most toxic and showed completely inhibited mycelial growth of S. rolfsii at 75% concentration. Clove extract was highly toxic and showed complete inhibition of R. solani at 50% conc. and F. oxysporum at 75% conc. On the contrast, the other essential oils of lettuce, ground nut, rockets and caraway did not cause any toxic effect against all pathogenic fungi under study compared with controls. In field experiments T. harzianum was the most effective in controlling the disease in all biological control treatments in this study. followed by T. virde, while P. fluroscence was the least one. The best control of R. solani root rot of sugar beet was by seed coating followed by infestation with bioagent before pathogen or applies of bioagent together and soil infestation in the same time. Seed soaking in essential oil and plant extract gave significant reduction on disease symptoms. Fungicide and Anise oil gave the highest reduction damping off (20.28%) and root rot (10%) followed by thyme oil. Garlic clove extract and onion extract were moderate in their effect. Artemisia extract gave the lowest percentage of reduction. Field results indicated high significant differences between sugar beet varieties under study. The highest percentage of damping off (17.3%) was recorded in case of Avalon variety followed by kawamira variety (15.5%) and the lowest was recorded in Toscana and Monte Bianco (2.7%). The highest percentage of root rot was recorded in Avalon variety ( 24.9%) followed by kawmira. Positive treatments in disease control led to improving the growth parameters and increase the yield of sugar beet.