MTT: New DNA markers promote Finnish rye breeding

Jokioinen / FI. (mtt) Healthy dark rye bread is a staple of the Finnish diet, but nowadays most of the rye used by bakeries is imported from other countries. Rye is less widely cultivated in Finland than other crops because the subsidies are low and the plant is sensitive to weather conditions, meaning that the crop yield is often small and baking quality poor.

Teija Tenhola-Roininen, Research Scientist at Agrifood Research Finland (MTT), constructed a linkage map of rye in her doctoral research and found DNA markers that can be used to breed rye lines that are better adapted to the Finnish climate. The DNA markers she discovered will help select lines with a short straw and a good pre-harvest sprouting resistance. A short straw is beneficial because it protects the stalks from being beaten down by late summer rainfall. Pre-harvest sprouting resistance is important because sprouting before harvest reduces the falling number of rye and decreases the quality of the grain for the baking industry.

Doubled haploid has no secrets

Tenhola-Roininen used homozygous doubled haploid plants in her research. The two homologous chromosomes in these plants are identical. In natural conditions, rye is cross-pollinated and has two different homologous chromosomes, one from each parent.

«The advantage of using doubled haploids in plant breeding is that all their characteristics are manifest in the plant, making selection easier. In normal cross-pollinated rye some of the characteristics are recessive and therefore cannot be detected», Tenhola-Roininen explains. Doubled haploids allow researchers to speed up the breeding process of a new rye line by three to four years.

Research plants produced by anther culture technique

Tenhola-Roininen produced the doubled haploids using the anther culture technique. This is a process whereby the anthers are plucked from the florets and placed on a growth medium to allow new plants to grow from the microspores contained in the anthers.

Doubled haploid rye plants are produced by the anther culture technique either spontaneously or haploid plants can be treated with colchicine to duplicate their chromosomes. During the research project, doubled haploid formation was also promoted by applying cold stress to the plants and heat stress to the anthers.

In some breeding lines these treatments increased the spontaneous regeneration of doubled haploids while in others they reduced it. In certain lines, the most effective treatment proved to be storing the spikes of rye at 04° Celsius for a period of three weeks.

«At least ten percent of the green plants regenerated by anther culture were suitable for breeding. Generally the mortality rate of the plants generated by anther culture was high, a fact that will have to be taken into consideration when planning the use of rye doubled haploids in further research», Tenhola-Roininen points out.

DNA markers found on chromosome 5R

In order to find DNA markers, two rye populations were generated with various degrees of dwarfism (short straw) and pre-harvest sprouting resistance. The indicator used to measure pre-harvest sprouting was the alpha-amylase activity of grains, which correlates negatively with the falling number.

To find markers which indicated pre-harvest sprouting resistance, Tenhola-Roininen constructed a genetic map containing 281 DNA markers. It is the first genetic map of rye constructed using doubled haploid plants in the world. She discovered that one genetic region associated with sprouting resistance is located on chromosome 5R.

In addition to arbitrary DNA markers, Tenhola-Roininen studied DNA markers located on 5R because a dwarfing gene is known to be located on that chromosome. She developed a DNA marker which breeders can use to select the individuals with the short straw from their breeding material with an error margin of 13 percent. This DNA marker is now being tested in rye breeding.

About: The doctoral thesis by Teija Tenhola-Roininen, M.Sc. Rye doubled haploids – production and use in mapping studies» will be publicly examined at the University of Jyväskylä in the end of March 2009. Professor Teemu Teeri of the University of Helsinki will serve as the opponent and Professor Jari Ylänne of the University of Jyväskylä will serve as the custos (source).