Recently, seedling damping off and blight progressing from old to young leaves were found on medicinal plants of the family Labiatae (Rosmarinus officinalis, Lavandula sp., Salvia officinalis and Thymus vulgaris). A fungus was isolated from diseased tissues, in which the hyphae had diameter, ramification angle of about 90º, basal constriction, a septum next to the lateral hyphae, and other typical characteristics of the genus Rhizoctonia. The fungus was inoculated on healthy plants cultivated in plastic pots by brushing inoculum suspension on leaves (brushing) or by pouring the inoculum suspension on the surface of pots (soil infestation). On plants inoculated by brushing, disease symptoms occurred on all leaves four days after inoculation. On plants inoculated by soil infestation, leaf blight continued to ascent for ten days after inoculation under natural conditions. Based on colony morphology, mycelial growth, number of nuclei, identification of anastomosys group and subgroup, and on the teleomorph, the pathogen was considered to be Rhizoctonia solani (anamorph of Thanatephorus cucumeris). As disease symptoms were reproduced by artificial inoculation on plants and the fungus was reisolated on potato dextrose agar (PDA) from diseased tissues, R. solani was confirmed to be the causal agent of the disease.
medicinal plants; Rosmarinus officinalis; Lavandula sp.; Salvia officinalis; Thymus vulgaris
