GRAIN YIELD AND PROTEIN CONCENTRATION IN WINTER WHEAT CULTIVARS TESTED WITH AND WITHOUT NITROGEN FERTILIZER

Market prices and environmental concerns favor low-input wheat production systems and lower N fertilizer doses. To detect possible genetic differences regarding the adaptation to N deficiency conditions, we analyzed grain yield (GY) and grain protein concentration (GPC) data from yield tests with winter wheat cultivars, organized by NARDI Fundulea in Romania, in 40 very diverse environments (locations x years), with and without N fertilizer application in spring. Correlation between cultivar performance with and without N fertilizer for both GY and GPC was highly variable, depending on the environment. The strength of the correlation between N fertilized and not fertilized plots decreased with increasing N stress, estimated by the difference due to fertilization, for both GY and GPC. The cultivar effect on differences between plots with and without N fertilizer was significant for both yield and protein concentration, when tested against G x E interaction and only a small part of this effect was associated with the potential expressed under N fertilization conditions. Significant deviations from the general regression of performance under N deficiency stress against performance in N fertilized plots were detected in some cultivars for both GY and GPC. These deviations were too small to be of immediate practical importance, but might be useful in breeding for cumulating genes favorable in low N conditions. The relationship between GPC and GY was negative and significant under N fertilization, but not significant under N deficiency. This suggests that, under N deficiency stress, differences in dilution of proteins by carbohydrates accumulation play a less important role than differences in other mechanisms (like N absorption or translocation) in determining genotypic variation of grain composition. Our results suggest that, in breeding for low input conditions, direct selection in N deficiency conditions could be more effective than selection in non-stress conditions for GPC, but probably not for GY.