الفهرس 
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Abstract
Sugar beet root rot diseases are studied and the fungi are isolated from infected roots. Pathogenicity studies reveal that phome betae and rhizoctonia solani are the most virulent fungi. Sugar beet varieties differ in their susceptibility to infection fungal inoculation causes reduction in sugar contents of roots. Root exudates of both healthy and infected plants of the susceptible variety (polybelga) contain sucrose, glucose and fructose while those of the other variety (hezzano) contain sucrose and glucose only. Healthy root exudates contain histidine, aspartic acid and leucine, amino acids. Moreover, only polybelga exudates contain glycine, glutamic acid, alanine, tyrosine, tryptophane and methionine. Polybelga stimulates counts of microbial flora more than mezzano in rhisosphere in uninfected soil. Root-rot infection is recorded when sugars begin to accumulate in storage roots. The soils differ in the degree of infection according to their electric conductivity, saturation percentage and salinity. All fungicidal treatments decrease infection.