Physiological and biochemical responses to manganese toxicity in ryegrass (Lolium perenne L.) genotypes

We studied resistance to manganese (Mn) toxicity under acidic conditions and its relationship with nutrients such as calcium (Ca) and magnesium (Mg) in new perennial ryegrass (Lolium perenne L.) genotypes (One-50, Banquet-II and Halo-AR1) introduced in southern Chile, using the Nui genotype as the reference. Plants were grown in nutrient solution at increased Mn concentrations (0–750 μM) at pH 4.8, and physiological and biochemical features were determined. Under higher Mn concentration, the One-50 genotype had a significantly lower relative growth rate (RGR) of shoots and roots, whereas in the other cultivars this parameter did not change under variable Mn treatments. Increasing the Mn concentration led to an increased Mn concentration in roots and shoots, with Banquet-II and Halo-AR1 having higher Mn in roots than shoots. Shoot Mg and Ca concentrations in all genotypes (except Banquet-II) decreased concomitantly with increasing Mn applications. In contrast to the other genotypes, Banquet-II and Halo-AR1 maintained their net CO2 assimilation rate regardless of Mn treatment, whereas the chlorophyll concentration decreased in all genotypes with the exception of Banquet-II. In addition, lipid peroxidation in Banquet-II roots increased at 150 μM Mn, but decreased at higher Mn concentrations. This decrease was associated with an increase in antioxidant capacity as well as total phenol concentration. Banquet-II and Halo-AR1 appear to be the most Mn-resistant genotypes based on RGR and CO2 assimilation rate. In addition, Mn excess provoked a strong decrease in Ca and Mg concentrations in shoots of the Mn-sensitive genotype, whereas only slight variations in the Mn-resistant genotype were noted. When other evaluated parameters were taken into account, we concluded that among the perennial ryegrass genotypes introduced recently into southern Chile Banquet-II appears to be the most Mn-resistant, followed by Halo-AR1, with One-50 being the most sensitive.