Genotypic variation in seedling root architectural traits and implications for drought adaptation in wheat (Triticum aestivum L.)

Abstract

A crop's ability to explore the soil profile and extract available water at different depths is largely determined by root system architecture. For instance in wheat (Triticum aestivum L.), it has been suggested that a narrow and deep root system can provide better access to deep soil moisture. Such root systems are particularly beneficial for rain-fed regions where crops rely heavily on stored soil moisture at depth, as encountered in the eastern Australian wheat belt. Thus, by targeting desirable root architectural traits, wheat breeders could increase genetic gain for yield in response to the growing demand for food. Yet, selection for these below-ground traits is challenging because roots are difficult to measure and are under complex genetic control. The aim of this project was to develop new phenotypic and molecular selection tools to facilitate selection for root architectural traits in Australian wheat breeding programs targeting terminal moisture stress adaptation. This project focuses on narrow seminal root angle and high number of seminal roots in wheat seedlings; two proxy traits for desirable mature root system architecture. Firstly, to overcome the lack of efficient root screening methods, a high-throughput and cost-effective method for phenotyping seminal root angle and number in wheat was developed, using clear pots in a controlled environment growth facility. Compared to pre-existing phenotyping methods, the newly developed method successfully provided higher heritability, greater repeatability, and better efficiency in terms of time, space, and labour. Further, the clear-pot method revealed a high degree of phenotypic variation for both seminal root traits. Subsequently, to test the ability to introgressed allelic variation for seminal root angle into elite Australian wheat cultivars via phenotypic selection, backcross tail populations for both narrow and wide root angle were developed, using the clear-pot method. Rapid shifts in both population distribution and allele frequency were observed after just two rounds of selection. Further, comparison of the tail populations revealed some genomic regions under selection, for which marker-assisted selection appeared successful. Hence, genetic diversity can be exploited via phenotypic and molecular selection to target desired root system architecture in wheat breeding programs.

Management of crop water under drought: a review

“…For wheat, physiological and root research studies evidence the significant contribution of roots to higher drought resistance (e.g. Sanguineti et al 2007;Manschadi et al 2008;Palta et al 2011). Wasson et al (2012) give an overview of selection strategies for root improvement of wheat in Australia.…”

Arbuscular mycorrhizae modify winter wheat root morphology and alleviate phosphorus deficit stress

“…Wheat root system characteristics are of fundamental importance to soil exploration and below-ground resource acquisition especially under suboptimal soil conditions (Manschadi et al 2008). Root architectural traits such as shallower root growth angles, enhanced adventitious rooting, and greater dispersion of lateral roots, along with increased root hair number and length and mycorrhizal associations, represent adaptations that enhance soil exploration and lead to more efficient P acquisition (Lynch 2011).…”

Development of a novel semi-hydroponic phenotyping system for studying root architecture

“…WinRHIZO). The root architectural traits achieved can be divided into two general categories: topological properties (describing the pattern of root branching) and geometric properties (such as the growth angle of root axes) (Manschadi et al 2008). Both traits are critical in studying root architecture (Lynch and Brown 2001;Kato et al 2006;Manschadi et al 2008).…”

“…The root architectural traits achieved can be divided into two general categories: topological properties (describing the pattern of root branching) and geometric properties (such as the growth angle of root axes) (Manschadi et al 2008). Both traits are critical in studying root architecture (Lynch and Brown 2001;Kato et al 2006;Manschadi et al 2008). According to Fitter (1991), five types of data are required to reconstruct a three-dimensional model of a root: the number of internal and external links (without and with top meristem, respectively); the length of the links; the distribution of branches within the root, i.e.…”

“…Several non soil-filled methods for evaluating roots are available, including hydroponic, aeroponic and agar-plate systems (Gregory et al 2009). The soil-filled root observation chambers (Manschadi et al 2008) or rhizotrons (Wiese et al 2005), and growth pouches (Bonser et al 1996;Liao et al 2004) are often used in studying roots. More recently, an improved pouch system was developed by Hund et al (2009) for rapid measurement of maize (Zea mays L.) root systems during the first days of lateral root growth.…”