Supercharging wheat: Ancient genetic process provides opportunity for wheat breeding

29 Mar 2019 --- Wheat makes up half of the global calories consumed either directly or as animal feed. An important paper now marks a shift in how breeders might approach wheat breeding to meet increased demand, using previously untapped sources of variation. The research, funded through IWYP (International Wheat Yield Partnership) highlights the role of radiation use efficiency (RUE), how sunlight is converted into plant mass, in increasing the yield potential of wheat – how we can increase plant biomass without sacrificing grain yield – which has previously been a significant challenge.

The paper, Elucidating the genetic basis of biomass accumulation and radiation use efficiency in spring wheat and its role in yield potential, is co-authored by Dr. Ryan Joynson of EI’s Anthony Hall Group and Dr. Gemma Molero of Matthew Reynold's team at International Maize and Wheat Improvement Center (CIMMYT). 

According to Dr. Joynson, the ancient part of the process is the variation found in landraces and the progenitors of synthetic hexaploids (collectively the “exotic” material), represent old variation techniques that have been isolated from conventional breeding programs.

“In the future, we can expect to see an integration of much higher levels of genetic variation through increased use of ‘exotic’ material in attempts to alleviate current genetic bottlenecks restricting improvement using current strategies from wheat breeding,” he tells FoodIngredientsFirst. 

The markers identified in this paper allow for tracking of favorable RUE and yield genetic variation in breeding populations through marker assisted breeding at CIMMYT. “Along with shedding light on how strategic crossing of exotic material into breeding programs can be done while also successfully maintaining yield, an issue which has traditionally deterred breeders from attempting this,” Dr. Joynson explains. 

This research highlights:

• Identification of genomic regions affecting RUE and biomass accumulation in spring wheat.
• How increases in RUE can be achieved through strategic integration of “exotic” wheat into breeding programs.
• Identification of common genomic regions affecting yield, biomass and radiation use efficiency.
• Enrichment of genes related to photoprotection in genomic regions associated with RUE at various growth stages.
• Identification of untapped variation in wheat that can be harnessed and used by scientists and breeders.

The challenges
Thanks to Norman Borlaug’s green revolution, led from CIMMYT, the development and improvement of dwarf varieties of wheat have led to a drastic increase in wheat yields over the better half of the 21st century. Yet, this consistent increase has wavered in recent years, say the authors. 

Continually increasing wheat yields is challenging, increasingly so when we must more than double them if we are to sustainably feed 10 billion people by 2050, half of whom will rely on wheat as a staple for bread, noodles and more. At current rates, we are predicted to only get to 38 percent increased wheat yields by 2050, which would mean a significant shortfall.

The challenge is the well-known trade-off between things such as grain weight/number and biomass. The research asks: “Is it possible to reduce the leafy portion of a plant enough to boost harvestable product such that other aspects, including radiation use efficiency and nutrient uptake, are not disrupted or diminished?”

Alternatively, how do we increase biomass and the relative efficiency of photosynthesis, without reducing the harvestable portion of the crop – the grain?

The researchers note that photosynthesis itself is can be “inefficient.” So, it must be possible to find a happy medium between less biomass, more grain and more efficient photosynthesis. Where better to start than to identify genes and genetic regions underpinning all of these traits in elite lines of wheat?

By growing 150 types of wheat, then mapping the differences in growth to differences at the genetic level, it was possible to understand areas of commonality in desired traits for crop improvement.

According to Dr. Joynson, incorporation of exotic material into populations may also increase the arsenal of disease resistance genes within breeding populations providing greater levels of robustness to new disease strains.

“Wheat is ideal for this in part because of its polyploidy (number of genomes). The coming together of the three wheat sub genomes is thought to have only occurred in nature small number of times leading to quite severe bottlenecks in variation, especially in the case of the D subgenome (the most recently integrated of the three),” he continues. “Integration of synthetic hexaploids will alleviate this issue through providing novel genetic variation in the D genome (along with the A and B genomes).”

A new resource for breeders
Through analyzing new variations in elite wheat lines, while looking for the genetic markers underpinning and linking traits such as radiation use efficiency, biomass, yield, grain number, grain weight, etc., the researchers have provided an essential resource for scientists and breeders to exploit.

Namely, markers for use in marker-assisted breeding, that will help increase desired outcomes – such as biomass, thousand-grain weight and radiation use efficiency – while avoiding the trade-off between grain weight and grain number, or between biomass and harvest index, the authors note.

The study represents the completion of two years of work looking at 150 wheat varieties, using a genome-wide association study to analyze 31 different traits. Among the genetic regions identified, several were found in specific areas common to grain yield, biomass and radiation use efficiency.

Another important aspect of the work was the investigation of the effect of sources of new variation into elite lines of wheat. Comparing elite wheat varieties alongside “exotic” sequences such as landraces and synthetic wheat, the researchers pinpointed areas of interest for future breeding programs, i.e., where more variation can be introduced into the best wheat varieties for the desired outcomes.

By Elizabeth Green