الفهرس 
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Abstract
This study was planned to determine occurrence of Alternaria blight on coriander root rot on sage and wilt on basil in some governorates, to identify their fungal pathogens and to test their capabilities in diseases infection. Performance of silicon sources in suppressing the in vitro fungal growths and in reducing the disease incidence as well as their effects on plants growth and yields (seeds, herb & essential oil) were determined. Also, electron microscopic examinations (TEM & SEM) were used through plant and fungus cells to investigate the role of silicon in controlling the diseases. Occurrence (%) of blight disease (coriander) were (24.5-29.9%) in both seasons of survey, (19.8-25.1%) for root rot (sage) and (25.5-31.8%) for wilt (basil). Eight, seven and fife fungi were isolated and from infected tissues of these plants, respectively and A. alternata (blight), R. solani (root rot) and F. oxysporum f.sp. basilici (wilt) gave the highest frequency (%) in isolation and they were virulent in pathogenicity tests. The positive effects of silicon sources in the in vitro and in vivo experiments were confirmed, since they suppressed the fungal growth, decreased disease incidence, improved plant growth and increased plant yield and some important components of plant tissues and essential oil. Potassium silicate was the best treatment in all experiments as soaking (seeds), dipping (seedlings) and spraying (plants) treatments followed by calcium silicate, while sodium silicate was the least effective one. Electron microscopy examinations revealed that silicon has positive effects on plant health, which induce resistance against plant diseases.