WP3 COBRA Editorial – Improving breeding efficiency
Jörg Peter Baresel (WP3 leader)
As pointed out in the previous editorial written by Maria Finckh and Odette Weedon, the main virtues of populations, in contrast to homogeneous varieties, are a higher resilience and the capability to evolve, adapting themselves to different environmental conditions by natural selection.
Both capacities depend on a presence of a high number of diverging genotypes within the populations.
On the other hand, it might be desirable to apply artificial, in addition to natural selection, in order to improve performance and quality traits.
Every kind of selection leads to a reduction of the number of genotypes within a population. This is in contrast to the virtues of populations mentioned above, potentially reducing adaptability and plasticity. One problem is therefore to find the right balance between population size and selection intensity.
Another problem is that a high number of genotypes have to be tested simultaneously, if the characteristics of a population are intended to be maintained. Conventional breeding techniques, aimed at the identification of suitable single lines, are here mostly not applicable. Moreover, in self-pollinating species, we also need methods to enhance cross-pollination among many genotypes, in order to increase the proportion of favorable gene combinations within the population in the following generations.
Finally, selection has to be more environment-specific, in the extreme case specific to single farms, comprising selection by or with farmers.
All this require new approaches in breeding methods and technology. In addition, suitable basic populations, with different levels of diversity and adaptation are needed as a starting point. The WP3 of COBRA is a comprehensive set of research activities on all the mentioned aspects, comprising both cereals (wheat and barley ) and legumes (peas)
Beside marker-assisted selecion, several methods of improved mass selection are being tested by different partners within WP 3.
Selection based on single seeds, mainly for grain protein content, but also for grain weight, is currently being tested in Denmark. Some of the first results were very interesting, but the final data evaluation is still pending. Single seed selection is, however, restricted to a few traits, which, apart from the genotype, depend on the field heterogeneity, competition with neighboring plants and the position of the grain within the spike. Heritability is therefore expected to be low. On the other hand, this may be in part compensated by the extremely high number of individuals which may be comprised in the selection.
Single plant selection could be a way to test larger numbers of genotypes (several thousands). Positive results have been reported, mainly by Fasoulas and coworkers, but also in earlier reports. It is however, controversially discussed (if discussed at all), because the growing conditions of single spaced plants are different from those in dense stands.
Nondestructive phenotyping techniques may allow for evaluating large numbers of genotypes, and increase the range of possible assessments.These are mainly spectrometric measurements and the analysis of digital images, comprising the range of visible light, near infrared and thermic radiation. The traits, that can be assessed in this way, are mainly ground cover and related traits, such as biomass and leaf area index, as well as a few parameters indicating senescence, diseases and drought stress. More sophisticated methods comprise three-dimensioal analysis of the plant architecture; this is done mainly in highly automatized pot experiments on single plants. Though these results are difficult to interpret, the concerns of the relevance of single-plant selection seem here to be countered by enthusiasm for the new technologies. Field phenotyping methods especially are a valuable supplement, but not a replacement for the destructive measurements.
Figure 2. A high-throughput phenotyping “Phenotrac 4” platform developed at Technische Universität München, carrying many different sensors (Photo: Technische Universität München)
Another important aspect of breeding populations is recombination. While in populations of cross-pollinating species, this occurs spontaneously, it is more difficult to achieve in self-pollinating species. If hundreds or even thousands of genotypes are comprised manuale crossing is certainly too laborious. One approach, that we are currently investigating in wheat, is to exploit spontaneous outcrossing using xenia as marker. Adapted populations of winter and spring wheat, carrying genes conferring blue aleurone genes, have been established at the technical university of Munich; using cross pollinated plant material carrying this gene, F1 seeds can now easily be identified, and sorted out using automatic seed sorters. Approximately 2 % of cross pollinated seeds could be indentifed in an experiment carried out at Freising in 2015.
Figure 3. Color markers for identifying cross-pollination: Blue aleuron and purple pericarp, compared with normal seeds
Several new composite cross populations (CCPs)have been created by the technical university of Munich. These comprise CCPs based on high-yielding and high quality winter and spring wheats. Moreover, a bulk of about 700 different, not adapted wheats has been established, with the aim to maximise genetic diversity.
Figure 4. Crossing schemes for the establishment of new composite cross populations
Certainly, the time frame of COBRA is limiting; most of the topics require additional scientific work and are being continued in followup research programmes. The role of COBRA is actually, to initiate new areas of research, supplying both the methodology and plant material.
The next editorial will be written by Tove M. Pedersen and we look forward to hearing more about the results from WP4 on “Socio-Economics and Legislation”.