Abstract: Wheat grown in Mn-deficient soil has been widely observed to produce much reduced yields. Breeding for Mn-efficient wheat genotypes adapted to Mn-deficient soils would represent a long-term solution for wheat agronomy. To characterize the physiological basis of Mn efficiency in wheat genotypes would facilitate the breeding programs for producing Mn-efficient wheat. Using a solution culture and a soil culture system in the present study, a Mn-efficient UK wheat genotype Maris Butler and a Mn-inefficient UK wheat genotype Paragon have been compared with a Mn-efficient Australian wheat genotype C8MM in the responses to Mn deficiency in order to characterize the Mn efficiency in these wheat genotypes. Results showed that in solution culture, Maris Butler grown under Mn deficiency had 77% relative dry matter yield of control plants that were grown under Mn sufficiency, whereas C8MM and Paragon had 60% and 58% relative dry matter yield of their respective controls. Results from the soil culture demonstrated that relative dry matter yield remained high for Maris Butler and C8MM (53% and 56%, respectively), whereas the value for Paragon dropped to 33%. In terms of dry matter yield and photosynthetic efficiency, Maris Butler demonstrated Mn efficiency in both solution culture and soil culture, whereas C8MM showed Mn efficiency only in soil culture. Results also demonstrated that under Mn-depleted supply in soil, plants of C8MM had a significantly higher ability in Mn uptake, whereas plants of Maris Butler showed a higher internal Mn use efficiency in comparison with plants of Paragon. Results from the present study indicate that the ability of C8MM to accumulate higher amounts of Mn is the basis of the improved Mn efficiency of this genotype in comparison with Paragon, and in Maris Butler there is a higher internal use of Mn expressed as an improved photosynthetic efficiency in conferring its Mn efficiency. It is suggested that more than one mechanism has arisen in wheat to confer tolerance to Mn deficiency.

Key words: Mn accumulation, Mn deficiency, Mn efficiency, wheat genotype