Inhibition of Verticillium Dahliae and Rhizoctonia Solani Growth by Solid Phosphate Sludge Amendments

In Morocco, phosphate processing generates large quantities of sludge which amass, form fillings, reduce arable land and distort the landscape. Phosphate wash sludge is rich in mineral elements. In order to recover some of these mineral elements including phosphorus, we considered using this sludge in a nursery as a substrate.

The aim of the study was to check the effect of solid phosphate sludge amendment on some of the main soil-borne pathogens: Verticillium dahliae Kleb. and Rhizoctonia solani Kühn.

The pathogens have been isolated and identified in the laboratory of Plant Pathology and Postharvest Quality of INRA-Kenitra. Phosphate wash sludge used was originated from the Khouribga phosphate treatment sludge disposal site. Different concentrations of phosphate sludge (0, 10, 30, 50, and 100 g/l) were tested on a PDA-based medium, in three replicates. The inhibitory effects on mycelial growth were measured and compared with those on the soil used by nurseries (Maamora forest soil). Petri dishes with PDA alone were used as control. The same concentrations (10, 30, 50 and 100 g/kg) were tested in vivo on two varieties of tomato and on Faba Faba bean for Verticillium dahliae and Rhizoctonia solani, respectively.

The results of this study showed that there was significant growth inhibition at different concentrations of solid Phosphate sludge amendments in vitro. The highest inhibition percentage was observed at 100 g/l of phosphate sludge amendments with 42% and 75% for Verticillium dahliae and Rhizoctonia solani. The high concentrations of phosphate sludge have shown lower disease severity of Verticillium dahliae on the tomato plants and a disease index of Rhizoctonia solani on the Faba bean plants.

Based on these results, we can recommend that solid phosphate sludge can be used or mixed with other substrates in nurseries.