Next generation of Plant Breeding: Molecular Breeding.
Next generation of Plant Breeding: Molecular Breeding.
Over the last decades, plant breeding has moved from being a completely phenotyping-based process to having an increased reliance on some level of genotype-based selection. Genomic selection is a form of marker-assisted selection in which genetic markers covering the whole genome are used to improve quantitative traits.
Using genetic pools of male and female parents cause heterosis resulting in high performing varieties. Markerassisted selection helps to select traits of interest such as productivity, resistance or tolerance in order to speed up the development of new varieties.
We wanted to take a look behind the scenes. Therefore we spoke with ASUR Plant Breeding Nuno Almeida.
As a molecular breeder can you answer one quick question? Does heterosis exist in barley?
Yes, there are hybrids that are superior to the mean value of their parents or superior to the best parent. But we want to beat the check no matter whether with a conventional line or other hybrid barley varieties. So, we are interested in the “commercial heterosis”.
What does it exactly mean?
That means we can have a huge heterosis effect but if the parent’s performance is poor the heterosis effect might not be good enough to make a hybrid commercially appealing. To balance this aspect, breeders need to select good performing parents for their crosses.
When did researchers start working on hybrid barley?
According to a review on hybrid cereals by Professor Friedrich Longin (TAG, 2012)* one of the first recessive nuclear male sterility gene had already been described in the United States in the year 1940. This awoke the interest in hybrid barley. Then, public institutions conducted several trials on heterosis and seed production systems creating the balanced tertiary trisomic hybridisation system and first hybrid cultivars.
In addition to the balanced tertiary trisomic hybridisation a CMS system with a reliable single dominant restorer gene was also described in 1979. Almost 15 years had passed when Paul Bury, barley breeder at New Farm Crops, Ltd. (now Syngenta), decided to restart activities on CMS hybrids. More recently, other plant breeding companies like Ackermann and ASUR Plant Breeding also invest in their CMS hybrid barley breeding programmes. At present, Syngenta and SAATEN-UNION are the only providers of sixrow winter hybrid barley varieties on the market.
In other hybrid crops like maize or rye heterotic groups exist. How is it in barley?
The development of heterotic pools in barley is still in the early stages. ASUR Plant Breeding has different genetic pools of male and female parents. First the best parents are selected, the next step is to separate the parental groups as well as possible. We aim to have a perfect balance between seed production and heterosis effect of the hybrids.
Where is the CMS in barley coming from?
The commercially used CMS system is based on wild barley Hordeum vulgare ssp. spontaneum. ASUR is using backcrossing as a breeding tool to implement CMS into our female lines. Therefore, our CMS hybrids are created without any GMO technologies.
What kind of breeding technologies are you using apart from backcrossing?
We are using marker-assisted selection and genomic selection.
Backcrossing of parental lines in a green house
Sounds complicated. What is it?
Traditional plant breeding programs mainly rely on phenotypes being evaluated in several environments; selection and recombination are solely based on the resulting data and information deriving from pedigrees if available. Marker-assisted selection is a tool to help breeders to select the material at early stages. It is an indirect selection process in which a trait of interest is selected based on a marker (morphological, biochemical or DNA/RNA variation) that is linked to a trait of interest (e. g. productivity, disease resistance, abiotic stress tolerance, phenological traits or quality) rather than on the trait itself. Genomic selection is a form of marker-assisted selection in which genetic markers covering the whole genome are used for improving quantitative traits. This strategy requires a good phenotypic characterisation of large breeding populations.
What are the advantages of using those technologies in hybrid barley breeding?
At the beginning I explained that selecting good parents as well as separating them into groups are two key factors for successful hybrid barley breeding. Genomic selection is helping us to realise it. By using this technology we can identify and maintain heterotic groups within the breeding program. Furthermore, we are using marker-assisted selection to control the presence of resistance or quality genes in the parental lines in order to filter the parental combinations for testing. The result is a high performing hybrid barley variety
What is the future of molecular plant breeding at ASUR?
In the future, we will continue to screen our material with molecular markers that explain completely or a large part of the trait associated with it. These markers can be used to choose the parents for crossing or to select the progeny of one cross that has the target allele in segregation. The high throughput genotyping will continue to be used to access the diversity of our breeding pool (genetic relatedness to determine heterotic patterns) and to develop new markers as new phenotypic data is created from current traits of interest or traits that breeders expect to be important in the future.
*Longin, C.F.H., Mühleisen, J., Maurer, H.P. et al. Hybrid breeding in autogamous cereals. Theor Appl Genet 125, 1087–1096 (2012).