Modern wheat semi-dwarfs root deep on demand: response of rooting depth to drought in a set of Swiss era wheats covering 100 years of breeding

Abstract

Breeding for enhanced rooting depth and root biomass in deeper soil layers is a promising strategy to adapt wheat (Triticum aestivum L.) plants to drought periods. We evaluated (1) the extent of indirect selection of root traits during the last century of wheat breeding and (2) how it affected the variety performance under well-watered conditions compared to gradually developing drought stress. Fourteen bread wheat genotypes covering 100 years of Swiss wheat breeding were grown in 1.6 m tall columns in the greenhouse under well-watered and drought conditions. Root parameters, such as rooting depth and root biomass and above ground parameters were determined at flowering and maturity. Rooting depth showed a negative trend in response to year of release under well-watered conditions but not under early water stress. Modern varieties responded with enhanced root allocation to deeper soil layers. Consequently, rooting depth was positively correlated with plant height at well-watered conditions but not under early water stress. Considerable genetic variation for rooting depth among modern varieties indicates that the trait is selectable without strong alteration of plant height. We conclude that modern varieties adjusted rooting depth to water demand.

Effects of Low Water Availability on Root Placement and Shoot Development in Landraces and Modern Barley Cultivars

“…The modification of rooting patterns (distribution, morphology, density) in response to changes in soil water status has been described for wheat. Root dry weight, length and density of wheat changed its vertical distribution in response to both early and late water stress [48][49][50], and a similar phenomenon of root compensation was observed [51] in a study with adult wheat plants grown in soils with contrasting humidity at the top and bottom soil layers. When the top layer was dry and the bottom one was wet, the plants had a larger root system than when grown in fully wet soils, which indicated enhanced root growth in the wet soil part when it was stimulated by water stress in another soil area.…”

The soil organic carbon stabilization potential of old and new wheat cultivars: a <sup>13</sup>CO<sub>2</sub> labelling study

“…Four wheat (Triticum aestivum L.) cultivars from the Swiss wheat breeding program (Fossati and Brabant, 2003;Friedli et al, 2019) with different breeding ages were selected: Mont-Calme 268 (introduced in 1926), Probus (1948), Zinal (2003 and CH Claro (2007). Generally, more recent cultivars of this program on average have more shallow roots and lower root biomass under well-watered conditions compared to the older cultivars (Friedli et al, 2019). CH Claro was selected as a modern variety with relatively deep rooting.…”

“…One way to evaluate the effect of breeder's selection on root characteristics and subsoil carbon cycling is to compare old and new varieties of the same breeding programme. For the Swiss wheat breeding programmes, the selection process reduced the mass and depth of roots under well-watered conditions but modern genotypes enhanced root allocation to deep soil layers under drought (Friedli et al, 2019). The negative trend of rooting depth was also present in other breeding programmes (Aziz et al, 2017), but has not been observed consistently (Cholick et al, 1977;Feil, 1992;Lupton et al, 1974).…”

“…Deep rooting is also proposed by breeders to decrease the effect of drought in climates where deep soil water is available during the main cropping season (Wasson et al, 2012). Increased rooting depth is also proposed as a strategy to mitigate the effects of climate change in temperate climates as exemplified for the Swiss plateau (Friedli et al, 2019). Yet, for improving yield and resource uptake, the proposed root ideotype is steep, cheap and deep (Lynch, 2013) with less biomass and branching in the upper part of the soil (Wasson et al, 2014).…”

“…Therefore, the present study used four different bread wheat cultivars from a century of Swiss wheat breeding (Fossati and Brabant, 2003;Friedli et al, 2019) to test the hypothesis that wheat cultivars with shallow rooting systems and lower root biomass result in less subsoil OC stabilization over the course of a growing season. The experiments were carried out in large mesocosms, which allowed to study the plant-soil system under controlled conditions that closely resemble a field situation.…”