Abstract
We examined three different-ploidy wheat species to elucidate the development of aboveground architecture and its domesticated mechanism under environment-controlled field conditions. Architecture parameters including leaf, stem, spike and canopy morphology were measured together with biomass allocation, leaf net photosynthetic rate and instantaneous water use efficiency (WUEi). Canopy biomass density was decreased from diploid to tetraploid wheat, but increased to maximum in hexaploid wheat. Population yield in hexaploid wheat was higher than in diploid wheat, but the population fitness and individual competition ability was higher in diploid wheats. Plant architecture was modified from a compact type in diploid wheats to an incompact type in tetraploid wheats, and then to a more compact type of hexaploid wheats. Biomass accumulation, population yield, harvest index and the seed to leaf ratio increased from diploid to tetraploid and hexaploid, associated with heavier specific internode weight and greater canopy biomass density in hexaploid and tetraploid than in diploid wheat. Leaf photosynthetic rate and WUEi were decreased from diploid to tetraploid and increased from tetraploid to hexaploid due to more compact leaf type in hexaploid and diploid than in tetraploid. Grain yield formation and WUEi were closely associated with spatial stance of leaves and stems. We conclude that the ideotype of dryland wheats could be based on spatial reconstruction of leaf type and further exertion of leaf photosynthetic rate.
Highlights
In arid and semi-arid regions, plants have evolved with large root systems for competing and adapting to water-limited environments as a result of natural selection [1,2,3,4,5]
It was found that all the parameters including leaf spatial angles and relevant morphological traits generally significantly increased from diploid to tetraploid wheats, but there were no significant changes from tetraploid to hexaploid wheats (Table 2)
It can be concluded that the domestication from diploid to tetraploid wheat was a process in which plant canopy became more well-structured by changing biomass allocation from belowground to aboveground
Summary
In arid and semi-arid regions, plants have evolved with large root systems for competing and adapting to water-limited environments as a result of natural selection [1,2,3,4,5]. Strong individual competitiveness for a crop species is closely related to more resources allocation into its vegetative organs, which improves the acquisition of resources such as water and nutrients, but reduces grain yield [6,7,8]. Modern wheat crop cultivars have evolved with less individual competitiveness but high reproductive allocation and population yield through strenuous plant breeding effort. High-yielding modern hexaploid wheats have a small root system with weak competition ability of individual plant and more resource allocation to reproductive growth, leading to an increased harvest index [6,11,12,13]. Large root systems are generally associated with strong individual competition for water and nutrients, which in turn reduces crop population yield. Large leaves could lead to low light transmittance through the canopy affecting canopy photosynthesis and population yield [20,21,22]
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