Abstract
Trait-based breeding is essential to improve wheat yield, particularly when stress adaptation is targeted. A set of modern and underutilized wheat genotypes was examined in a 2-year field experiment with distinct seasonal water supply. Yield formation and drought response strategies were analyzed in relation to components of Passioura's yield-water framework based on phenological, morphological, physiological, and root characteristics. Limited water supply resulted in 60% yield loss and substantially lower water use (37%), water use efficiency (32.6%), and harvest index (14%). Phenology and root length density were key determinants of water use. Late flowering underutilized wheat species with large root system and swift ground coverage showed greatest water use. Leaf chlorophyll concentration and stomata conductance were higher in modern cultivars, supporting their high biomass growth and superior water use efficiency. While, lower chlorophyll concentration and stomata conductance of underutilized wheats indicated a water saving strategy with an intrinsic limitation of potential growth. Harvest index was strongly dependent on phenology and yield components. Optimized flowering time, reduced tillering, and strong grain sink of modern cultivars explained higher harvest index compared to underutilized wheats. Cluster analysis revealed the consistent differentiation of underutilized and modern wheats based on traits underlying Passioura's yield-water framework. We identified physiological and root traits within modern cultivars to be targeted for trait-based crop improvement under water-limited conditions. High capacity of water use in underutilized genetic resources is related to yield-limiting phenological and morphological traits, constraining their potential role for better drought resistance. Still some genetic resources provide adaptive features for stress resistance compatible with high yield as revealed by high harvest index under drought of Khorasan wheat.
Highlights
Grain yield is the product of numerous developmental processes during crop growth
Continental climates as found in central-eastern Europe are distinguished by a higher proportion of in-season rainfall compared to stored soil moisture as source of crop water supply
Our results showed a significant association of early vigor with water use only in the dry year 2012, suggesting secondary associations of this trait with phenology and root length density (Figure 2)
Summary
Grain yield is the product of numerous developmental processes during crop growth. It is a trait governed by multiple genes and highly influenced by environmental conditions. Wheat drought response analysis (van Ginkel et al, 1998; Blum, 2011) This complexity becomes evident when attributes contributing to yield loss mitigation in a given environment are not useful in other water-limited environments (Richards, 2006). Despite these difficulties, wheat yield was remarkably increased over the second half of the 20th century in all wheat growing environments (Calderini and Slafer, 1998; Fischer et al, 2014) as a result of genetic improvement, enhanced input of production factors, water and nitrogen (Sinclair and Rufty, 2012), and a synergy between them (Richards et al, 2014). In dry regions, yield increase was below breeding progress registered for high yielding environments (Trethowan et al, 2002; Graybosch and Peterson, 2010)
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