FIRST REPORT OF Rhizoctonia solani CAUSING DAMPING-OFF AND ROOT ROT DISEASE ON Tetraclinis articulata SEEDLINGS

Rhizoctonia solani (Kühn) is a soil-borne, necrotrophic fungus causing damping off, root rot and stem canker in many cultivated plants worldwide. Recently, R. solani was isolated from thuya [Tetraclinis articulata (Vahl.) Mast.] seedlings showing damping-off disease in Sidi Amira Forest nursery, northwest Morocco. A pure culture of R. Solani, originally isolated from (5 weeks) T. articulata diseased seedlings, was used as inoculum of growing media with a (3:1,v,v) mixture of peat/vermiculite filled in 400 ml plastic containers with 50 wells. For the control containers, mock inoculum was added in each well. Pregerminated seeds of T. Articulata, brought from a Kourifla forest stand, were sown in a set of 4 containers for each treatment. Seedlings were grown up in a glasshouse in separated blocks to avoid any risk of contamination. After 3 weeks, pre-emergence, post-emergence damping-off, root rot and stem necrosis were observed in seedlings grown in containers with inoculated substrate while control sets remained asymptomatic. Koch’s postulate is verified by reisolating R. Solani from roots and hypocotyl of seedlings grown in inoculated growing media. Pathogenicity test revealed that pre-emergence, post-emergence mortality rate, disease index and growth parameters were significantly different comparing to control.