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Reduced root cortical cell file number improves drought tolerance in maize

Authors:

Chimungu JG, Brown KM, Lynch JP

Source:

Plant Physiology, 2014

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Abstract:

We tested the hypothesis that reduced root cortical cell file number (CCFN) would improve drought tolerance in maize (Zea mays L.) by reducing the metabolic costs of soil exploration. Maize genotypes with contrasting CCFN were grown under well-watered and water-stressed conditions in greenhouse mesocosms and in the field in the USA and Malawi. CCFN ranged from 6 to 19 among maize genotypes. In mesocosms reduced CCFN was correlated with 57% reduction of root respiration per unit root length. Under water stress in the mesocosms, genotypes with reduced CCFN had between 15% and 60% deeper rooting (D95), 78% greater stomatal conductance, 36% greater leaf CO2 assimilation, and between 52% to 139% greater shoot biomass than genotypes with many cell files. Under water stress in the field, genotypes with reduced CCFN had between 33% and 40 %deeper rooting (D95), 28% lighter stem water δ18O signature signifying deeper water capture, between 10% and 35% greater leaf relative water content, between 35% and 70% greater shoot biomass at flowering, and between 33% and 114% greater yield than genotypes with many cell files. These results support the hypothesis that reduced CCFN improves drought tolerance by reducing the metabolic costs of soil exploration, enabling deeper soil exploration, greater water acquisition, and improved growth and yield under water stress. The large genetic variation for CCFN in maize germplasm suggest that CCFN merits attention as a breeding target to improve the drought tolerance of maize and possibly other cereal crops.