Differential tolerance of manganese among cultivars of Triticum aestivum

Thirty cultivars of Triticum aestivum differed in tolerance of manganese (Mn) as determined by relative root growth in solution culture. Based upon a root weight index (RWI = root weight in the presence of 500 μM Mn divided by control root weight), Mn tolerance ranged from 0.08 to 0.88. All Canadian Western Red Spring (CWRS) cultivars tested were Mn sensitive. Cultivars bred for high yield were more Mn tolerant, especially 'Norquay' (RWI = 0.88) which was the only cultivar with a RWI > 0.70. The cultivars 'Norquay' and 'Columbus' were selected as standards for Mn tolerance and Mn sensitivity, respectively. 'Norquay' showed maximum root growth at 100 μM Mn, a concentration which was toxic to 'Columbus', and differential tolerance was maintained up to 1000 μM Mn in solution. Differences between 'Norquay' and 'Columbus', grown in excess Mn, were also observed in the accumulation of biomass with time. In contrast with previous studies, Mn tolerance was positively correlated with Al tolerance (R2 = 32.7, p = 0.001) in the cultivars tested.