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 p H, where aluminum (AI) 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 po ts with sand fed with a nutrient solution (pH 4.5) to which MnSO4. 4H( 2)O was added. The biomass of plants (cv. Arabian) grown during one mo nm 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, Be agle, Borba, and TTE 9201) during the complete growth period (Experime nt II). During this experiment the effects of Mn concentrations on the net photosynthetic rates, stomatal conductance, photosynthetic capaci ty, photochemical efficiency of PSII, quantum yield of photosynthetic non cyclic electron transport and leaf content of chlorophylls, and ca rotenoids in the several cvs. were studied. The final biomass and yiel d were taken as the ultimate criteria for ranking the cvs. It was conc luded that 10 ppm Mn concentration was optimal for the growth and 50 p pm the lowest limit to produce toxicity which indicates that triticale was rather tolerant. All the physiological parameters determined afte r one month of growth and the performance of the photosystems were neg atively affected by the Mn concentrations, but the changes were not su fficient 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 conc entration. The plants of the cv. TTE 9201 were the least affected as f ar as photosynthetic parameters are concerned.