Trends in Root Architecture for Historical and Contemporary Wheat Cultivars of Uruguay

The configuration of the root system architecture in the soil determines the ability of a plant to access water. Studies in Australia indicate that narrow root growth angle is desirable for wheat varieties grown throughout the eastern region, where deep soils with high water-holding capacity and low in-season rainfall occurs.

In this study we examined historic and contemporary wheat cultivars, grown in Uruguay, South America, from 1918 – 2015, to investigate whether selection and breeding in changing environments are reflected in the root system architecture. A total of 120 cultivars were evaluated for seminal root angle (SRA) using the ‘clear-pot’ phenotyping method, where a narrow SRA in seedlings is associated with narrow root system architecture in adult plants.

Different SRA phenotypes were observed, ranging from 58.5^o to 116.5^o. There was a trend of increasing SRA for cultivars released from 1918 to 1980. However, from 1980 a dramatic increase in SRA diversity was observed. This coincided with the introduction of new high yielding CIMMYT spring germplasm and the release of local long cycle germplasm selected for early sowing and double purpose management. Many above-ground traits, such as tillering and flowering time, influence the dynamics of water demand. It is likely that adoption of this new germplasm introduced genetic diversity for new combinations of below- and above-ground traits, which may have led to different pathways for improved yield. From 2002, the breeding program also changed field management practices, adopting no-tillage system. No-till production improves water infiltration and soil structure, thus a high proportion of contemporary cultivars displaying narrow SRA suggests it may be advantageous under these conditions.

Improved understanding of trait interactions and annual phenotyping of elite lines in the breeding program using the ‘clear pot’ method will provide an opportunity to monitor and optimise root system architecture for the local environment.