Effects of breeding history and crop management on the root architecture of wheat

Abstract

28Aims 29 Selection for optimal root system architecture (RSA) is important to ensure genetic gains in the sustainable production 30 of wheat (Triticum aestivum L.). Here we examine the idea that past wheat breeding has led to changes in RSA and 31 that future breeding efforts can focus directly on root traits to improve adaptation to a target environment. 32 Methods 33We conducted three field trials using diverse wheat varieties, including modern and historic UK varieties and non-UK 34 landraces, tested under contrasting tillage regimes (non-inversion tillage versus conventional ploughing) or different 35 seeding rates (standard rate versus high rate). We used field excavation, washing and measurement of root crowns 36 ('shovelomics') to characterise RSA traits, including: numbers of seminal, crown and nodal roots per plant, and crown 37 root growth angle. 38 Results 39We found large differences among genotypes for all root traits. Modern varieties generally had fewer roots per plant 40 than historic varieties. There were fewer crown roots and root angles were wider, on average, under shallow non-41 inversion tillage compared with conventional ploughing. Crown root numbers per plant also tended to be smaller at a 42 high seeding rate compared with the standard rate. There were significant genotype-by-year, genotype-by-tillage and 43 genotype-by-seeding-rate interactions for many root traits. 44 Conclusions 45Smaller root systems is likely to be a result of past selection and may have facilitated historical yield increases by 46 reducing below-ground competition within the crop. The effects of crop management practices on RSA depend on

Symmetric response to competition in binary mixtures of cultivars associates with genetic gain in wheat yield

“…Higher radiation use efficiency is independent of photosynthesis and respiration at leaf level and relates to an erectophyl canopy that favours more radiation and higher nitrogen concentration in leaves at the bottom of the canopy. The less competitive phenotype has a smaller root system (Aziz et al, 2017; Fradgley et al, 2020) with compensatory higher nitrogen uptake per unit root length (Aziz et al, 2017)…”

“…In wheat adapted to winter–rainfall environments, phenotypes with reduced competitive ability and high yield feature more erect canopies with relaxed extinction of nitrogen relative to the extinction of radiation that lead to higher radiation use efficiency, and smaller root system with higher nitrogen uptake per unit root length (Aziz et al, 2017; Richards et al, 2019; Sadras & Lawson, 2013; Sadras et al, 2012). Modern UK wheat cultivars generally had fewer roots per plant than historic cultivars and landraces, and smaller root systems have been interpreted in terms of reduced below‐ground competition (Fradgley et al, 2020). Likewise, modern Chinese wheat cultivars had smaller root systems than old landraces (Fang et al, 2021).…”