Variation in rooting strategy and resource use efficiency amongst spring wheat (Triticum aestivum) cultivars
High variability in rainfall together with high evaporative demand creates severe constraints for crop growth and yields in semiarid environment where sustainable food security is needed. Crop research has, therefore, to focus on sustaining the competitiveness of production in these environments where optimal root architecture can be important in determining uptake and resource use efficiency of water and nutrients. The aim of this thesis was to identify variation in genetic by environment interaction amongst wheat cultivars in root system architecture and to establish on how it relates to water and nutrient acquisition and drought tolerance/resistance. Initial laboratory studies revealed variation in rooting strategies amongst cultivars. This was followed by two soil bed studies and one field study, which investigated the association of rooting strategies with WUE, NUE and crop performance in the absence and presence of moisture stress (wet and dry) and of nitrogen (0 and 60 kg N ha-1). Laboratory, soil-bed and field trials were conducted to test the hypothesis that selection of optimum rooting traits would improve WUE, NUE and production of wheat cultivars in dry semi-arid environments. Results showed that wheat cultivars have two distinct rooting strategies, one with large root systems and fast extension and the other with small root systems and slow extension. The enhanced resource acquisition strategy associated with large, rapidly extending roots was shown to be successful in all environments. It resulted in fast earlier plant vigour, higher WUE, NUE and DM yield.