ZINC SUPPRESSES SIRODESMIN PL TOXICITY AND PROTECTS BRASSICA NAPUS PLANTS AGAINST THE BLACKLEG DISEASE CAUSED BY LEPTOSPHAERIA-MACULANS

Zinc sulphate, when added to the growth medium of Leptosphaeria maculans, decreased the production of the toxin sirodesmin PL by 75%. When supplied as a nutrient to Brassica napus plants, zinc was also able to suppress the toxicity of sirodesmin PL deposited on punctured cotyledons or leaves. Finally, zinc (ZnEDTA, ZnSO4 and ZnCl2) supplied to B. napus plants grown in the glasshouse, increased partial resistance to the blackleg disease. The treated plants did not escape the disease, but it developemore slowly than in the untreated ones. Plants receiving zinc remained free from any symptoms longer, and developed the crown necrosis responsible for the lodging at a later stage than the controls. Phytoalexin synthesis (mainly brassilexin) was not increased by the treatment, hence the protective effects of zinc on plants is likely to be due to the suppression of the toxic effects of sirodesmin PL in planta. © 1990.