Ten isolates of S. rolfsii, collected from Kafr El-Sheikh and Beni-Sweif Governorates were studied for their morphological characteristics and secondary metabolites. Isolates were differed in their mycelial growth rates on PDA medium as well as numbers and diameters of sclerotia. Five isolates, three i.e., SrK1, SrK2 & Srk5 (Kafr El-Sheikh) and SrB4 & SrB5 (Beni-Sweif) grow faster than the other isolates, where they completely covered the whole surface of PDA medium plates (90mm) after 72 h incubation at 28°C. Kafr El-Sheikh isolates (SrK1, SrK2 & Srk5) gave the highest number of sclerotia (145.3 sclerotium/plate) and the largest size of sclerotia compared with the other isolates. Under greenhouse conditions, all tested isolates of S. rolfsii affected severely the sugar beet plants during seedling and mature stages compared with the control. At the seedling stage, isolates i.e., SrK1, SrK2, SrB2, SrB4 and SrB5 were highly aggressive on sugar beet plants where they caused the highest percent of damping-off with lowest percent of survival plants. At mature stage, there were insignificant differences among the tested S. rolfsii isolates in inducing sugar beet root rots except SrB1 (Beni-Sweif). The high performance liquid chromatography (HPLC) analysis of culture filtrates of S. rolfsii isolates exhibited clear variations in exerted phenolic acids. In this respect, ferulic and cinnamic acid were not detected in any one of cultural filtrates of tested S. rolfsii isolates. Meanwhile, gallic acid was recorded in detectable amounts in filtrates of SrK1 and SrK4 isolates (4.30 and 4.92 µg/ml, respectively). However, the other tested S. rolfsii isolates were unable to excrete this phenol into the growing media. Chlorogenic acid was detected only in filtrates of SrK5 and SrB3 isolates (37.51 and 30.84 µg/ml, respectively). Also, all isolates of S. rolfsii were able to produce both indol acetic acid (IAA) and oxalic acid.

Key worlds: Sclertioum rolfsii, isolates, sugar beet, damping off, root-rot disease, phenolic acids, indol acetic acid and oxalic acid