Changes over time in the adaptation of barley releases in north-eastern Spain

The objective of this study was to characterize grain yield and adaptation of barley cultivars released in recent decades in north-eastern Spain. Ten six-rowed and 10 two-rowed barley genotypes were grown in eight environments. Mean yields varied among environments between 1.7 and 5.8 t.ha(-1). New releases showed higher mean yields and were specifically adapted to nonlimiting growing conditions. The average genetic advances were estimated as 40.7 and 32.9 kg.ha(-1).years(-1) for two- and six-rowed genotypes, respectively, in the four most productive environments. Old genotypes, with lower overall gain yields, were specifically adapted to the poorer sites. A negative genetic gain, estimated as - 14.8 kg.ha(-1).years(-1), was recorded for six-rowed cultivars in the four poorest sites. No significant association was observed between heading date and year of release. Variations in carbon isotope discrimination (Delta) were examined to assess whether changes in adaptation could be partially explained by shifts in the genotypic transpiration efficiency (TE) over time. In the most favourable environments, new releases showed the highest grain yields and carbon isotope discrimination values (Delta). By contrast, older cultivars had constitutively lower as and therefore higher TEs. These results suggest a genetic association between low TE and yield potential and specific adaptation to stress-free conditions so that selection for yield under favourable conditions could have resulted in an indirect downward genetic shift in the TE of modern cultivars.