Responses of biomass and several photosynthetic indicators to manganese excess in triticale

Triticale (X Triticosecale, Wittmack) is generally accepted as a very rustic crop which can grow in difficult soils such as those with low pH, where aluminum (Al) and/or manganese (Mn) are frequently in excess. The first aim of the present work was to establish the parameters for the future evaluation of Mn excess tolerance. Plants were grown in pots with sand fed with a nutrient solution (pH 4.5) to which MnSO4 ·4H20 was added. The biomass of plants (cv. Arabian) grown during one monm in a range of Mn concentrations (2, 2.75, 11, 16.5, 22, 33, and 44 ppm) was determined in Experiment I. Subsequently a shorter range (10, 50, 100, and 200 ppm) was chosen and used with four cvs. (Arabian, Beagle, Borba, and TTE 9201) during the complete growth period (Experiment II). During this experiment the effects of Mn concentrations on the net photosynthetic rates, stomatal conductance, photosynthetic capacity, photochemical efficiency of PSII, quantum yield of photosynthetic non cyclic electron transport and leaf content of chlorophylls, and carotenoids in the several cvs. were studied. The final biomass and yield were taken as the ultimate criteria for ranking the cvs. It was concluded that 10 ppm Mn concentration was optimal for the growth and 50 ppm the lowest limit to produce toxicity which indicates that triticale was rather tolerant. All the physiological parameters determined after one month of growth and the performance of the photosystems were negatively affected by the Mn concentrations, but the changes were not sufficient to be used for an early (one month old plants) ranking of the cvs. consistent with the biomass and final grain yield. However, all the results agree that the cv. Arabian was the most sensitive because it suffered the strongest decreases and was affected by 50 ppm Mn concentration. The plants of the cv. TTE 9201 were the least affected as far as photosynthetic parameters are concerned.