Genotype by environment interaction for grain yield and carbon isotope discrimination of barley in Mediterranean Spain

Carbon isotope discrimination (Delta) has been found to be either positivel y or negatively related to grain yield of small grain cereals when grown in contrasting environments. In order to clarify a possible association betwe en grain yield of barley (Hordeum vulgare L.) and Delta of mature kernels, five 6-rowed and five 2-rowed barley cultivars were evaluated in 22 rainfed environments of northern Mediterranean Spain. Analyses of variance suggest ed that the genotypic Delta values were more consistent across environments than the genotypic yields. Genotypexenvironment (GxE) interaction for grai n yield was further explored by fitting an AMMI (additive main effects and multiplicative interaction) model. The first 2 multiplicative axes were fou nd significant. The AMMI2 model provided more accurate estimates of genotyp ic yields within environments than the conventional unadjusted means across replicates. AMMI2 estimates were used for input into cluster analysis, gro uping environments that ranked genotypic yields similarly. Three major grou ps were obtained, with average yields of 2.42 t/ha (cluster I), 3.06 t/ha ( cluster II), and 5.16 t/ha (cluster III). The genotypic ranking for Delta d id not vary substantially across clusters, but it changed for grain yield. The average genotypic yields in the low-yielding cluster I ranked opposite to those in the high-yielding cluster III, suggesting the existence of a cr ossover point at an intermediate yield level. The association between grain yield and Delta for genotypic means within clusters was variable. In clust er I, yield and Delta tended to be negatively related, whereas they were po sitively related in clusters II and III. Genotypes with lower Delta, i.e. w ith higher transpiration efficiency, performed better in low-yielding envir onments (mostly those grouped in cluster I). On the contrary, a high genoty pic Delta was of advantage in medium (cluster II) and high-yielding environ ments (cluster III). This observation supports the assumption that drought tolerance and high yield potential under non-limiting growing conditions ma y be antagonistic concepts in barley. Genotypic means for kernel number per m(2) and Delta were consistently and positively related within clusters, s uggesting that a constitutively high Delta may have been driven by a large genotypic reproductive sink. The convenience of using nas a selection crite rion in areas exhibiting a considerable GxE interaction for grain yield is discussed.