Study identifies the best breeding strategy for more productive wheat varieties

A study in which José Luis Araus, professor at the Faculty of Biology of the University of Barcelona and researcher at Agrotecnio, has participated, has identified the most efficient strategy to obtain wheat varieties that are more productive and resilient under adverse environmental conditions such as drought or high temperatures.  As a result of this discovery, the researchers have considered how to obtain more productive varieties and point out that the most economical and effective strategy for the genetic improvement of crops consists of a two-phase process: in the first, varieties that show the highest yield potential are chosen, and in the second, those that have best adapted to the environment in which they were grown are selected. This approach could have significant economic implications, as it would reduce the number of locations needed to select advanced breeding lines.  The work, a review of the scientific literature published in the journal Trends in Plant Science, included the participation of researchers Alejandro del Pozo from the University of Talca (Chile) and Victor Sadras from the University of Adelaide (Australia).  A possible solution to a scientific debate  Increasing the yield potential of wheat and its resilience to factors such as drought or high temperatures —which are becoming more frequent due to climate change— is essential to feed a global population that is expected to reach 9.5 billion people by 2050.  The genetic selection of varieties is a key resource in this challenge, but it is an iterative process that can take years: it consists of crossing individuals that show the best agronomic and physiological traits and subjecting the resulting filial generations to selection processes.  The scientific debate on what is most appropriate is ongoing: some argue that selection should be based on the grain’s yield potential under optimal conditions, while others believe it should be based on the grain’s ability to adapt to stress conditions.  Araus believes that the study’s results show that selecting varieties under very severe environmental conditions “is not the best breeding strategy, as it may limit their yield.” He illustrates this point: “Selecting based on physiological efficiency in water use (understood as the photosynthesis-transpiration ratio) would be negative in terms of productivity.”  “On the other hand —continues the UB professor—, what is good under optimal conditions is also good under not-so-optimal ones: a high-yield candidate selected in the best environment will normally outperform varieties that have not been selected for their potential yield, and this will occur across a wide range of conditions, such as moderate or severe droughts.”  The only exceptions would occur in extremely stressful environments. But even in that case, Araus defends the mentioned strategy: “Even in a climate change context like the current one, where we will increasingly face more extreme situations, we must opt for this strategy, since the productivity of varieties developed under extreme conditions would not be profitable for European farmers.”  A more economical and effective strategy  The study has allowed researchers to establish what would be the most appropriate strategy for carrying out this genetic selection process. According to the results, the first phases —the first six or seven generations— should be centralized in an optimal agronomic environment (with the best possible conditions) and varieties should be selected according to their maximum possible yield. In the following phases, advanced lines with good agronomic quality should be sent for final selection to the specific area where they are to be cultivated —for a couple of additional generations— to identify the most locally adapted varieties.  This approach would have two main advantages. The first would be economic, since “reducing the number of sites where advanced lines are selected, prioritizing the development of well-managed crops in favorable environments, would also reduce the overall cost of breeding worldwide,” explains Araus. The second advantage would be efficiency: selecting in optimal environments is more efficient, as it minimizes factors that can confuse the breeder. “If conditions are optimal, the plant’s genetic potential is better expressed. Conversely, under suboptimal conditions (lack of water, poor soils, or variable temperatures) there is more environmental noise, which makes it harder to identify the best individuals,” argues the UB professor.  Key agronomic and physiological traits  The research also identified agronomic and physiological characteristics associated with better performance. “Some of the traits that make plants perform better, especially considering that water is the most limiting factor for productivity, are those that increase their ability to capture water: it’s not so much about being highly efficient in using water, but about being able to use more of it than other varieties,” explains Araus.  This can be achieved, for example, “with roots capable of exploring the soil in depth when there is no water, or taking advantage of surface water when it rains or when the crop is irrigated,” he adds.  Likewise, crop architecture is key: light should be distributed as evenly as possible between the upper and lower layers of the plants. “For all the leaves to contribute to light use, the upper leaves should be as vertical as possible to let radiation pass through and reach the lower parts,” details the researcher.  Other determining factors would be the production of more spikes per unit area, an increase in the number of grains, and a higher canopy photosynthesis rate per unit of solar radiation. “All this is achieved through suitable architecture and good water uptake conditions that keep the stomata open,” he highlights.  According to Araus, “there is no panacea or single trait,” but rather a set of characteristics that allow improving the efficiency of radiation and water use.  Finally, the study also analyzed transgenic pathways to increase yield, but “so far they have not produced significant results.” Moreover, “the results of adaptation to specific stress conditions such as drought are rather modest,” concludes the researcher. 

Text and image: UB press office