Abstract

Morphogenesis, cell differentiation, sclerotial formation and melanogenesis of a fungus depend on growth conditions. The present work aims to study the effect of some chemicals on the growth parameters of Rhizoctonia solani, which is the main causal organism of many diseases as damping off disease of many crops such as Phaseolus vulgaris. Different concentrations of hydrogen peroxide H₂O₂ and Ethylenediaminetetraacetic acid (EDTA) were studied. EDTA showed an inhibitory activity with decreasing sclerotia formation and its pigmentation (melanogenesis), also hyphae became hyaline. This isolate which lacks melanin, was nominated as hyaline Rhizoctonia (HR). Hydrogen peroxide showed highest sclerotia formation and increase in its pigmentation. This isolate, which forms melanin, will be nominated as dark Rhizoctonia (DR). It caused a higher disease index to seeds of P. vulgaris than did HR. Melanin is a virulence factor. The disease index was higher by DR than HR. DR exhibited less protein content, but more diverse proteins than HR. DNA similarity between DR and HR was about 90%. Superoxide dismutase (SOD) was detected in a higher amount in DR than HR. Catalase could not be detected in either DR or HR. EDTA is promising potential drugs for combating pathogenicity.

Key words: Rhizoctonia, superoxide dismutase, pathogenicity, melanin, DNA, EDTA.