Assessing the variation in traits for manganese deficiency tolerance among maize genotypes

Deficiency of manganese (Mn) is a serious problem reducing crop yields on calcareous and sandy soils throughout the world. In maize, limited knowledge is available on genotypic differences in tolerance to low-Mn supply and the physiological mechanisms underlying this tolerance. In the present study we have evaluated twelve maize genotypes (inbred lines) for their tolerance to Mn deficiency. The evaluation was based on measurements of how low-Mn supply affected shoot biomass, leaf Mn concentrations, maximum quantum efficiency of photosystem II (F-v/F-m), photosynthetic net CO2 assimilation, root length, Mn uptake and root-shoot Mn translocation. Tolerant genotypes were able to maintain optimum F-v/F-m values under a longer period of Mn deficiency with less reduction of foliar Mn concentration and photosynthetic rate, resulting in less reduction of shoot biomass, compared to sensitive genotypes. Efficient root uptake of Mn and root-to-shoot translocation of Mn also contributed to improved tolerance to Mn-deficiency. The metal transport genes YSL, NRAMP, ZIP, CAX and MTP, involved in root Mn uptake, root-to-shoot Mn translocation and vacuolar Mn homeostasis, were more highly expressed in the efficient genotype K22compared to sensitive genotype BY815. With respect to breeding of maize cultivars with improved Mn-efficiency, the time-course of changes in F-v/F-m values in response to Mn-deficiency provides a useful screening index for low-Mn tolerance.

Automated summary

Efficient genotypes of maize were found to maintain optimal photosynthetic efficiency, reduce foliar Mn concentration and photosynthetic rate under prolonged Mn deficiency, resulting in less reduction in shoot biomass compared to sensitive genotypes. Key metal transport genes involved in Mn uptake and translocation were more highly expressed in the efficient genotype, suggesting potential for breeding maize with improved Mn-efficiency. The time-course of changes in photosynthetic efficiency in response to Mn-deficiency could serve as a useful screening index for low-Mn tolerance in maize breeding programs.