Iron toxicity is recognized as one of the most widely distributed nutritional disorders in rice, with considerable areas of lowland rice showing some nutritional disorders associated with iron toxicity.
The problem: Iron (Fe) toxicity is widespread in rice fields in Africa when soils derived from iron-rich rocks are inundated with water. Under these anaerobic conditions, insoluble Fe III is reduced to the more soluble Fe II, which is readily taken up by rice roots. At soil Fe II concentrations above 300 ppm, severe yield losses are incurred in sensitive rice varieties. A study in Côte d’Ivoire, Ghana, and Guinea Conakry found that more than 50% of the lowland rice area was affected by iron toxicity (Chérif et al 2009).
Phase 2 Objective: Identify the best sources of tolerance for iron toxicity, elucidate the genetic control, and develop and test improved tolerant varieties under farmers’ and improved management practices.
Phase 1 research accomplishments/progress
• Inventory of existing African iron-toxicity-tolerant germplasm completed
A list of 181 accessions was compiled, including two sensitive checks. The material comprises accessions from different institutes (WARDA, IRRI, CIAT, and NARES). Six advanced bulk populations for evaluating iron-toxicity tolerance were dispatched from IRRI to WARDA and many segregating populations were sent to Nigeria (IRRI-Africa).
• Participatory varietal selection conducted for at least 10 iron-toxicity-tolerant lines at key sites in four SSA countries (Nigeria, Guinea, Burkina Faso, Benin) by WARDA
Two PVS trials were established at Banfora (Burkina Faso) and Edozighi (Nigeria) with a set of 181 entries. Farmers’ field days were organized at both sites, involving 60 farmers, with women in the majority, at Banfora and 43 farmers, almost exclusively men, attending the field day at Edozighi. The rating sheets collected at both sites are being compiled to record farmers’ choices and perceptions.
PVS in Nigeria, 2 December 2008
• Phenotyping for iron-toxicity screening at WARDA refined
Three approaches are being used to screen for iron-toxicity tolerance—field trials, pot trials, and hydroponics trials. The pot-trial protocol uses plastic pots filled with sand supplemented with Fe2+ as FeSO4. Optimal fertilizer (100 kg ha–1 N, 50–100 kg ha–1 P, and 60–100 kg ha–1 K) will be applied to allow normal growth of rice plants in order to avoid nutrient disorders. Forty genotypes were screened with this protocol using two concentrations of Fe2+ (300 and 900 ppm). The first symptoms observed were a reduction in plant height and tillering, whereas leaf bronzing appeared later. In parallel, 180 genotypes were screened in the field at hotspots in Edozighi (Nigeria) and in Banfora (Burkina Faso). Iron-toxicity tolerance was scored and grain yield will be determined as well as morpho-physiological traits. Hydroponic screening is being planned in collaboration with IRRI and the University of Hohenheim, Germany. The same 180 accessions will be screened for leaf bronzing score (LBS) and other morpho-physiological traits will be measured at IRRI.
A team of WARDA scientists and NARES partners inspecting a foundation seed production field for newly released rice varieties in Senegal