New wheat root ideotypes for improved resource use and efficiency and yield performance in reduced input agriculture

Abstract

The main objective of this study was to determine the impact of wheat root growth and morphology on the efficiency of nutrient uptake and hence yield and to explore how this interacts with selected environmental and agronomic parameters. The level of genetic variation for root development was assessed in a range of wheat genotypes in controlled environments along with the performance of a sub-set of lines with contrasting root characters under field conditions. Interactions with mycorrhizal fungi were also assessed.

A DNA based assay was developed that shows differences between root phenotypes of UK wheat varieties in field grown plants. The utility of the assay was assessed by comparing DNA results with those from soil washing experiments. Furthermore, it was assessed whether DNA-based assays can distinguish between genotypes that differ in root phenotype. Finally, it was determined whether DNA-based assays are sensitive to changes in root phenotype in response to soil treatments (e.g. nutrient input, soil tillage). This technology is a potential tool for plant breeders and for exploring variation within agronomic trials.

Plant roots interact with a complex microbial community in the soil, including microbes that enter into the root tissue. Prominent among these are the arbuscular mycorrhizal fungi (AMF), which can provide demonstrated benefits for plant growth. Here, an improved tool was developed to describe the diversity of AMF within roots and in the surrounding soil, and tested in a number of different wheat trials, looking at contrasts in treatments and varieties. The approach was to amplify a variable region of the 18S ribosomal RNA gene using AMF-specific primers, and then to pool samples and sequence using the Ion Torrent PGM^TMplatform. Reads are clustered into sets at approximately the level of species so that relative species abundance can be determined. The method revealed high species diversity of AMF in both roots and soil, and high spatial variation in communities from one plot to another. Future studies will need to be carefully designed to take this variation into account in order to detect the effects of variables such as depth in the soil, agronomic treatments, or crop varieties.

Quantification of cereal root systems during plant development to maturity raises several challenges. Cereal root systems are relatively large compared with more commonly explored model species such as Arabidopsis thaliana, and vary with plant genotype. Cereal roots are also highly dynamic during the cereal growth season and in response to environmental factors such as nutrient availability. This research aimed to quantify root phenotype in UK wheat varieties at four growth stages, using one of two methods: i) a flat bed filter paper based system to characterise roots at seedling stage; and ii) a metre-length rhizotube system to characterise roots at stem elongation, anthesis and maturity. Root responses to nitrogen supply were also assessed using the rhizotube system. Significant differences were found between varieties in root size and in rooting depth and root shape. The maximum rooting volume occurred at anthesis, with the majority of the root expansion being found between 0 cm and 30 cm deep in the rhizotubes. The overall increase in root size with development and depth depended on wheat variety but was significantly affected by the length of the growing season to anthesis. Changes in both root size and shape were found in response to nitrogen treatment, and in addition there was evidence of differences in the type of responses between varieties.

Taken together, the three strands of research have created methods and datasets of value to root researchers, agronomists and plant breeders that will furnish a toolkit useful in development of new varieties and cultivation methods for UK growers.