Variation for and relationships among biomass and grain yield component traits conferring improved yield and grain weight in an elite wheat population grown in variable yield environments

Grain yield and kernel size ( grain weight) are important industry traits for wheat in the water-limited environments of the north-eastern wheatbelt of Australia. These, and underpinning morphological and physiological traits, were evaluated in a population of recombinant inbred lines from the elite CIMMYT cross Seri/Babax, segregating for the presence of the rye translocation (T1BL.1RS). The population was examined to determine the variation among lines, relationships among traits, the extent of line x environment interactions, potential efficiency of direct and indirect selection, and to identify trait combinations that are associated with higher grain yield and grain weight. Transgressive segregation was observed for all traits, and line x environment interaction effects were frequently larger than line main effects. Across six environments ranging in yield from 202 to 660 g/m(2), the T1BL.1RS wheat-rye translocation had a positive effect on grain weight (+3.4%) but resulted in decreased grain number per m(2) (-6.5%) and grain yield (-3.1%). Realised selection responses indicated that broad adaptation was best achieved by selection for mean performance across the range of target environments. However, specific adaptation for performance in high- or low-yielding environments was best detected by direct selection in those types of environments. A group of broadly adapted Seri/Babax lines exceeded the mean of five cultivars grown commercially in the north-eastern wheatbelt by 8% for grain yield and 17% for grain weight. These Seri/Babax lines with both high grain yield and grain weight were associated with a combination of several traits: earlier flowering, reduced tillering, a greater proportion of tillers that produce grain-bearing spikes at maturity, high water-soluble carbohydrate stem reserves at anthesis, a higher proportion of competent florets at anthesis to maximise grains per spikelet leading to a high harvest index, and possibly a greater capacity to extract soil water. These results suggest a suitable ideotype for breeding high- yielding wheat cultivars with high grain weight adapted to environments with hotter, drier conditions during the post-anthesis period.