Soil and Mold Influences on Fe and Zn Concentrations of Sorghum Grain in Mali, West Africa

Iron (Fe) and zinc (Zn) deficiencies affect an estimated 3 billion people worldwide and are linked with cognitive and physical impairments, maternal and child mortality rates, and decreased adult work activity. To combat this "hidden" hunger, plant breeders in Mali are working to increase sorghum grain Fe and Zn concentrations. The objective of this study was to investigate soil and mold influences that affect Fe and Zn uptake and accumulation in sorghum grain. In southern Mali, soils from participatory sorghum variety trials and areas of different parent material and proximity to Shea (Vitellaria paradoxa) trees were analyzed for diethylenetriaminepentaacetic acid (DTPA)-extractable Zn and related soil properties, and sorghum grain was analyzed for Zn concentration. An inoculation trial was also performed at College Station, TX to determine if sorghum grain infected by the mold Curvularia lunata significantly increased grain Fe concentrations.

DTPA-extractable Zn concentration was highly variable with high concentrations found in soils under Shea tree canopies with high pH and organic carbon and derived from mafic, high Zn-content parent material. However, these high concentrations did not significantly affect grain Zn concentrations in sorghum grown outside of the canopy. Groundnut grown underneath the canopy is likely to be affected and warrants further investigation. In many cases, soil DTPA-extractable Zn concentrations were at deficient levels, thus hampering its correlation to sorghum grain Zn concentration and potentially limiting the expression of genetic Zn biofortification. Knowledge of soil DTPA-extractable Zn concentrations or basic soil properties such as pH, organic carbon, and soil parent material may aid in the location of suitable available Zn fields and overall biofortification efforts.

Grain Fe concentration was not significantly related to Curvularia lunata percent recovery or grain mold rating, but instead showed a relatively high variance by panicle, digestion batch, and grain subsample. Additional work is needed to address these sources of Fe variation so as to determine better if mold affects grain Fe concentrations.