Exploring relationships between root architecture and growth of UK wheats (Triticum aestivum L.)

Abstract

On Australian soils, where water is only available at depth during the grain filling period, growing deep rooting cultivars increased wheat yields by approximately 15%. Seedling root angle is associated with adult root system depth in Australian field-grown wheat cultivars (Triticum aestivum L.), but it is not yet known whether selection for root angle and rooting depth could benefit UK wheats. A soil-based, 3D, basket pot screen identified distinct root angle phenotypes (ranging from 35° to 52° from the vertical) among a selection of UK commercial cultivars. These phenotypes were generally stable despite varying soil water content, soil strength, and aerial temperature, but two cultivars showed significant changes in root angle in response to soil moisture. Cultivars Istabraq and Battalion displayed contrasting shallow and deep root angles, respectively. In fully factorial pot trials, with contrasting vertical soil moisture gradients and terminal drought treatments, genotype did not significantly affect early growth and physiology of young (tillering) wheat plants, but there were significant interactions with moisture gradient and water availability in some treatments. Under soil drying, ABA-mediated stomatal closure maintained Ψleaf in Battalion, whereas leaf decreased in Istabraq in the absence of changes in foliar ABA concentrations. This suggests contrasting water use strategies (isohydric Battalion and anisohydric Istabraq) are responsible for the observed physiological differences, rather than root angle. Field trials investigated whether these laboratory observations were correlated with root system development and yield of mature fieldgrown wheat. Soil cores taken from experimental wheat plots at Rothamsted Research’s Woburn farm were split at 10 cm intervals, and the number and positioning of roots and bio-pores at the exposed faces counted. Roots were washed from core sections to measure root length density by depth. Root length density declined with soil depth in all cultivars, and was not associated with seedling root angle phenotype, nor did yield correlate with root system traits. In the drier year only, Battalion had the most roots in the surface soil layers, which experienced greater soil drying under Battalion than under other cultivars. These studies contribute to the growing body of research on root system ideotypes in rainfed temperate climates, by identifying genetic variation in seminal root angle in high performing commercial wheat cultivars. While seedling root angle was not correlated with yield in field trials, it was associated with ability of roots to penetrate hard soils and access water in deeper strata of the soil profile. These traits would be especially beneficial during the grain-filling phase, and may potentially increase UK wheat yields during dry summers.