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Changed quality characteristics of malting barley
Dr. Markus Herz, Dr. Jennifer Groth, Dr. Wouter Vahl and Rudolf Cais from the Bavarian State Research Centre for Agriculture (LfL), Institute of Crop Production and Plant Breeding in Freising, have investigated these effects in more detail and were able to show that modern varieties already have a good tolerance to drought stress in the sum of their agronomic characteristics. In practice, the choice should therefore fall on a yield-stable variety with good malting quality [1].
Old varieties or exotic barley are on the whole less well adapted to our growing conditions and show weaker stress tolerance across all traits than modern varieties.
However, individual barley types show clear superiority in certain individual traits, such as water efficiency. Therefore, this well-characterised plant material can be used very well in breeding to specifically introduce these traits into superior varieties and thus further improve their stress tolerance. Here, the use of molecular genetic markers can also help to accelerate the process.
Winter malting barley would also be a good alternative for dryland sites.
Heat and drought are particularly hard on the summer malting barley (Picture: Andrius, Pexels)Heat, drought, extreme weather
It is now undisputed that climate change has reached us. Climate observations and models for the future clearly show that conditions for crop production in Germany are becoming more difficult. This is particularly clear from the increase in the CO2 concentration in the atmosphere and the temperature, which are documented by long-term measurements. Global radiation has shown a marked upward trend in recent years, especially in southern Germany, increasing the stress on crops.
Heat and drought as well as unpredictable regional extreme weather conditions already make it difficult to reliably produce sufficient malting barley with the necessary good quality characteristics.
From trials in the field and under controlled stress conditions, trends can be seen in what changes can be expected in malt quality and in the agronomic performance of barley.
Since 2009, several projects at the Bavarian State Research Centre for Agriculture have been investigating the reaction of spring barley to drought stress. In the case of spring barley, this is not only about yield, but also about the development or maintenance of brewing quality under the changing climatic conditions.
Heat and drought affect malting barley in different ways (Picture: BRAUWELT)Malting barley under climate stress
Defining climate stress in plants precisely is not easy. The plant is affected by heat and drought in different ways. These effects range from disturbances of the water and CO2 balance through the closure of stomata to the accumulation of undesirable metabolic products in the plant. Consequently, different reactions to stress occur, depending on the cause, for example due to drought or heat, and this also at different times of vegetation.
In order to be able to make as accurate a statement as possible about the plant's reaction to stress, there is therefore no choice but to work with a model that can simulate a specific type of stress at a specific point in the vegetation.
It has been shown that drought stress during ear emergence in cereals has a major impact on yield and, above all, on the quality of the grains, which plays an important role for processing into malt. Therefore, the occurrence of drought stress during ear emergence of spring barley was simulated in the LfL trials in the rolling greenhouse and in the glasshouse.
What effects does drought stress have on the quality of malting barley?
How does spring barley generally behave under drought stress? For this purpose, different varieties were examined under drought and irrigation in a special greenhouse that can roll on rails over the experimental stand when it rains.
At the same time, the intention was to find out whether individual varieties tolerate drought better than other varieties. Overall, all trials show that yields decrease under drought stress and that grain quality in the form of whole barley content also tends to suffer.
In the experimental model, the plants seem to adapt to the simulated drought by reducing the number of stalks that carry the grain. This still results in an acceptable grain quality.
In practice, however, weaker grain sorting is often observed at dry sites. With sufficient spring precipitation and subsequent drought, the plants can form many tillers and ears. Later, however, the water in the soil is no longer sufficient to form this large number of grains sufficiently.
Investigations of root growth on a very diverse assortment of spring barley could prove that under drought stress the plants very quickly and clearly reduce root growth and do not, as perhaps expected, try to find water in deeper soil layers through increased root growth.
The varieties do show differences in their reaction to drought stress in terms of root growth, but the available data do not confirm that older varieties develop more roots than current high-yielding varieties.
The processing quality of the malting barley plays a decisive role in the malthouse (Picture: BRAUWELT)Evaluation of malting barley varieties with the help of the Genotype Stability Index (GSI)
In order to include as many of the investigated traits as possible in the assessment of the varieties with regard to drought stress, the Genotype Stability Index (GSI) was calculated, which summarises the traits for each variety and outputs them as a single number [3].
The smaller this number, the better the genetically determined tolerance to drought stress. This shows that the newer varieties and breeding lines of the medium-sized companies involved in the project perform better across all traits than old varieties or exotic origins from arid regions.
In terms of processing quality, it is initially surprising that the crude protein content in the grain decreases under drought stress across all tested varieties. This would even be a positive development for brewing quality.
Presumably, under stress, the plants take up less nitrogen from the soil and also shift less to the grain. Here, therefore, the dilution effect does not seem to manifest itself in relation to yield under drought stress.
Under the experimental conditions, the processing quality of the barley therefore seems to deteriorate overall despite a lower crude protein content. Presumably, the change in the structure of the starch during grain filling plays a role here. For example, it has been shown in other studies that the gelatinisation temperature of the barley increases under dry conditions [4].
Winter malting barley could be an alternative - first trials indicate this (Picture: BRAUWELT)Winter barley as an alternative?
The trials with winter barley under drought stress conditions have not yet been completed. However, there are indications that winter barley reacts similarly to spring barley in terms of quality characteristics under drought stress, as can be seen from the example of the friabilimetre value. Together with the higher yield stability under critical conditions, winter barley could therefore definitely be an alternative for maintaining regional malting barley production in affected regions.
There are currently no neutral, confirmed results available on spring barley in autumn cultivation. In addition to winter barley varieties, spring barley in autumn cultivation under drought stress is currently being tested in the LfL's rolling greenhouse. It is quite possible that varieties with correspondingly good resistance and quality in areas with mild winters can keep up with both winter barley and spring-sown spring barley in terms of yield and quality. However, there is currently not enough data to make an official recommendation.
Literature
1. Herz, M.; Groth, J.; Vahl, W.; Cais, R.: „Welchen Einfluss hat der Klimawandel auf die Braugerste?“, BRAUWELT Nr. 19, 2020, S. 494–497.
2. Zingaretti, S. M.; Cascaes Inácio, M.; de Matos Pereira, L.; Antunes Paz, T.; de Castro França, S.: Water Stress and Agriculture, 2014, https://dx.doi.org/10.5772/53877.
3. Crossa, J.; Gauch, H.G.; Zobel, R.W.: „Additive main effects and multiplicative inter-actions analysis of two international maize cultivar trials”, Crop Sci 30, 1990, S. 493–500.
4. Schüll, F.: „Einfluss spezifischer Eigenschaften der Stärke auf den Brauprozess“, Dissertation TUM, München, 2012.
