Performance Story: Optimization of root development and photosynthesis parameters for yield increase/protection
Dr. Gopalan Selvaraj, National Research Council of Canada
Agricultural drought is well recognized as inadequate moisture for crop production. Additionally, sporadic moisture deficits that escape public attention also impact crop economics. Statistics Canada noted in one of the many drought years in Saskatchewan and Alberta: “Dry conditions during the growing phase in much of Canada's wheat belt contributed to lower crop yields.” Heat and drought exacerbate the stress conditions and affect many biochemical, biophysical and developmental aspects in plants. Every degree Celsius above the optimal temperature can cause as much as 6% yield reduction in wheat. Drought and heat impact crop productivity more than all other biotic and abiotic stresses combined.
As wheat breeders continue their quest for yield increase, protecting the genetic gains already achieved is also essential, especially in view of climate change. Ideal genotypes should yield well under optimal conditions and also perform at least satisfactorily to avert farm crises of stress conditions. Such types must retain grain quality and all other essential attributes. This is the challenge, a formidable one if beneficial genes are to be sourced from highly divergent cultivars. While varieties of vastly different adaptation - for example, Australasian and Canadian cultivars would be expected to show striking contrast, deploying the knowledge to Canadian varietal development would be protracted.
The aim of the project was to develop a knowledge base for deeply understanding the phenotypic and molecular genetic attributes of Canadian cultivars with contrasting stress responses, and to help construct the beneficial allele combinations. Roots gather nutrients and water, and water serves fundamental roles, one of which is to drive photosynthesis. Water uptake, transport, transpiration and utilization are all integral to the dynamics of plant performance. In wheat, the flag leaf provides much of the grain photosynthate. Designing crops with optimal root system has been difficult because of numerous challenges in studying the “hidden half”. The importance of the root system for wheat performance under dry conditions was recognized in the globally pioneering work done in Canada in the 1930s and 1960s. Durum varieties incorporating abundant roots as a trait sourced from an Algerian variety were indeed released half a century ago. Since then, there has been no such direct effort.
Thus, in this project, >100-year-old tall Algerian durum variety Pelissier that has been commercially grown in Saskatchewan until the 1980s and the “conventional height” Strongfield – the Canadian variety of largest cumulative acreage, along with a doubled haploid population of the two lines kindly provided by Agriculture and Agri-Food Canada, were studied. Phenotyping methods for root biomass and photosynthesis traits were investigated, and further the team has employed synchrotron-based root imaging as a potential method for analysis, in collaboration with Canadian Light Source (CLS) scientists.
Other key findings include:
As an adapted germplasm for western Canadian crop production conditions, Pelissier holds much promise as a source allele for well-timed root development and for stress-tolerant photosynthesis.
A linkage map of Pelissier x Strongfield has been constructed with usable SNP markers from the Ilumina 90K array.
Quantitative Trait Loci (QTL) for Root, Photosynthesis, Height, Lodging, LSC and various seed traits have been mapped. Doubled Haploid lines with potentially interesting phenotypes have been identified.
Global gene expression revealed intriguing patterns such as upregulation of genes in Strongfield under stress while Pelissier remained more stable.
The genetic intervals between the flanking QTL markers remain large and it is unlikely to be refined unless the marker repertoire is increased. Thus, further studies on finding beneficial alleles with tightly linked markers is required.