Today, four major genes are known in barley that induce flowering when the day length and temperature are appropriate. The photoperiod response gene Ppd-H1 in winter barley triggers flowering as soon as day length increases in spring. At the same time, the vernalization gene Vrn-H2 counteracts Ppd-H1; it permits flowering only when the plant has been exposed to low temperatures. After a sufficient cold stimulus, the vernalization gene Vrn-H1 induces the development of the reproductive meristem. In contrast, the vernalization gene Vrn-H3, like Ppd-H1, is thought to accelerate the late reproductive stages in barley.
In contrast to winter barley, the Ppd-H1 gene is mutated in spring barley and is therefore inactive. Moreover, the Vrn-H2 gene is deleted. Flower development is thus delayed in spring barley under long photoperiods, and does not require vernalization, allowing the plant to make use of the long growth period in temperate climates.
We are looking for genes that influence individual phases of flower development. This would allow flowering to be fine-tuned in different environments in order to increase yield. Drought shortens the time to flowering in barley. Long photoperiods affect primarily the later reproductive stages, stem elongation and spike development. The extensive collection of wild barleys from the Fertile Crescent held at our institute is a valuable source of new genetic variants, as systematic breeding of high-yielding varieties since the beginning of the last century has increasingly narrowed genetic variation in our elite varieties. In terms of evolutionary history, though, this is a short period of time, and most of the natural ancestors of our recent cultivars can still be crossed with them.
We investigated around 900 varieties of wild barley and crossed those that vary in their reproductive development with German barley cultivars. This gives rise to barley lines with differences in reproductive development and thus yield structure. The underlying traits and gene forms that cause this variation are passed on to the offspring. With the aid of molecular markers, we identify those regions in the barley genome that control spike development. As the barley genome has not yet been decoded, we align the identified genomic regions with the rice reference genome, which has already been sequenced. This allows us to identify flowering time genes in barley, as rice and barley are characterized by a similar gene content and gene order on the chromosomes.
We also use findings from plant genome research on Arabidopsis thaliana because the pathways that trigger flower development have already been thoroughly investigated in this plant. As many of the genes and functions involved are also functional in barley, it is possible to draw conclusions about the genetic regulation of flower development in barley.
Studies on the regulation of flowering time in barley are first carried out under controlled conditions in the greenhouse, where we test the effect of individual environmental parameters – day length, temperature and water – on the individual genes and traits. However, we have to study the effects of the different gene forms in wild and cultivated barley in the field before they can be applied in plant breeding. For this, we work with the Center for Agricultural Research in the Dry Areas (ICARDA) in Syria; ICARDA has the global mandate to research barley and agricultural production in semi-arid regions.
At this international agricultural research center, we are examining, under natural conditions in the field, the strategies barley uses to adapt to drought. We then carry out detailed genetic studies at our institute to identify the genes and gene regions that increase the crop yield of barley under dry conditions. This information is not only important for farmers in the Middle East, it also serves the breeding of cultivated plants in other parts of the world where they must adapt to increasingly dry summers.