Résumé
Iron toxicity is a widespread nutrient disorder of lowland rice systems in West Africa. Soluble (reduced) iron present in the soil solution under water-logged conditions is absorbed by the roots and accumulates in leaves. It causes severe yield reductions, associated with leaf discoloration and poor tillering and growth. During the last two years, field experiments were conducted at an iron-toxic lowland site at Korhogo in Cote d'Ivoire, in order to study interactions between the toxicity and nutrient amendments. Nine factorial combinations of nitrogen, phosphorus, potassium and zinc fertilizer applications were tested in one susceptible (Bouake 189) and one iron-toxicity-tolerant cultivar (CK4). P, K and Zn applications reduced iron toxicity symptoms and increased yield in both cultivars. Strong correlations were found between yield and scored leaf toxicity symptoms across seasons and treatments. The tolerant cultivar absorbed less iron or transported less to the leaves, indicating the presence of a physiological avoidance mechanism. At any given concentration of iron in the leaves, net photosynthetic rates were lower in the susceptible variety than in the tolerant variety. In summary, the tolerant variety owed its superior performance under iron toxic conditions partly to avoidance (less iron accumulation in leaves) and tolerance (superior photosynthetic potential in the presence of absorbed iron in the leaves). These mechanisms could be further enhanced through application of P, K and Zn. (Résumé d'auteur)