Using chemical and biological treatments to reduce the potential of potato leak caused byPythium aphanidermatum in Tunisia

Summary The effect of fungicides and the antagonistic fungusTrichoderma harzianum (Th) on the potato leak pathogenPythium aphanidermatum (Pa) was investigated in vitro. Rot was reduced by 73% to 89% when tubers inoculated withPa were treated by immersion in solutions (0.5% w/v) of the fungicides Ridomil MZ58. Dithane M45. Manebe 80 and Tachigaren 360. Complete protection was achieved by dusting inoculated tubers with Ridomil MZ58 diluted in kaolin at a final concentration of 0.1% (w/w). The biological treatments of dipping inoculated tubers in a conidial water suspension ofTh at 10⁸ conidia/ml or of dusting with a mixture of a barley culture ofTh and kaolin to a final concentration of 2×10⁹ conidia/g were as effective as the chemical treatments. Control was still effective when inoculated tubers were treated with Ridomil MZ58. Tachigaren 360 or the conidial suspension ofTh after 24h incubation at 25°C.