Growing malting barley amid climate change; the challenge of pre-harvest sprouting

By Karl Kunze
Graduate Student, Cornell University, School of Integrative Plant Science Plant Breeding and Genetics Section, advised by Dr. Mark Sorrells

If you recall from the 2021 season, you almost certainly heard of the challenging weather conditions experienced growing barley across the country. Despite some regions facing extreme drought, rain was particularly high for other regions during harvest, which was detrimental for growing areas and malting barley varieties not adapted to rain that late in the season. For the last few decades, malting barley varieties have been selected for less dormancy so that when harvested, the barley can be malted more quickly. The tradeoff, however, means that once the barley reaches maturity, the barley is highly prone to germinate if enough moisture is present in the environment and this is called pre-harvest sprouting. Given increasingly unpredictable weather events due to climate change, rain events at harvest are becoming more common at locations not typically used to such conditions.

Future barley breeding must focus on selecting barley varieties that are resistant to pre-harvest sprouting but will also germinate quickly in the malt house and produce high quality malt. Fortunately, there is plenty of genetic variation that barley breeders can integrate into new varieties that can be both resistant to pre-harvest sprouting in the field but also produce high quality malt.

The Cornell Small Grains Breeding Program has been measuring pre-harvest sprouting on both wheat and barley lines to select varieties that are resistant to the condition. We start by making note of when each barley line has reached physiological maturity, or when the barley grain has completed development and no green is left in the barley head. This requires some careful examination of spikes to ensure that the sample is at that point. If we sample too early, the grain may not have developed completely, and pre-harvest sprout scores may be artificially low. If we sample too late, we do not have an accurate measure of when the barley reached maturity and thus, we cannot compare to other experimental lines. After we harvest 5 mature spikes from each experimental plot, we then have the barley further ripen for 3 (for spring barley) to 4 days (for winter barley). Those samples from each plot are then placed into flat trays and consistently misted for 3 days in the greenhouse to simulate a rain event that would occur in the field. After those 3 days, the trays are then removed and each of the 5 spikes are scored on a 0-9 scale for visible signs of pre-harvest sprouting. A score of 0 indicates no visible signs of pre-harvest sprouting, low scores indicate some pre-harvest sprouting, and high scores show clearly visible green coleoptile (shoots) on most of the kernels in the spike.

For the 2022 year alone, we analyzed over 450 experimental winter lines and 100 experimental spring lines for pre-harvest sprouting, in addition to all of our variety trials and cooperative nurseries. In our experimental trials, we use the pre-harvest sprouting information for two purposes. One is to potentially map genetic variation within our experimental populations. The second is to eliminate lines that we find to have moderate to high pre-harvest sprouting susceptibility. We screen all variety trials, including cooperative nurseries, to make recommendations on the potential risk of growing varieties that are susceptible to pre-harvest sprouting.

Selecting for pre-harvest sprouting is a balancing act, ensuring barley has some dormancy so that it does not germinate in the field but not so much dormancy so that the grain will not germinate well in the malt house. Our research in measuring both pre-harvest sprouting and seed dormancy in a spring and winter barley population indicates that this balance can be achieved. In spring barley, some of our parent lines were very prone to pre-harvest sprouting and thus we have had to select for more dormancy. In our winter malting barley population, we have had the opposite effect, where most lines are sufficiently resistant to pre-harvest sprouting but may have excessive dormancy that would not be desirable for malting quality. Over the winter of 2021-2022, we had the opportunity to perform nano malting on approximately 170 experimental lines at two different malting timepoints. So far, we have found that most experimental lines have acceptable malt quality. We have significant variation of seed dormancy at our earlier timepoints. Most of our non dormant lines were resistant to pre-harvest sprouting based on our field tests. Continuing work and collaboration with growers, maltsters, brewers and support from AMBA has allowed us to make progress in achieving this balance.

——————————————————

This research was funded, in part, by the American Malting Barley Association (AMBA), an agricultural trade organization representing the interests of end users of malting barley, including maltsters, brewers, distillers, and food processors. Our work seeks to maintain a stable and high quality supply of malting barley for our members throughout the U.S. AMBA’s direct investment, supported by member dues, augments state and federal funds allocated for barley research.

The core of AMBA’s research program is applied barley breeding and related support programs, including basic research. Other support is provided for research projects on diseases, insect pests, variety evaluation, production, management, and malting quality. Significant progress has been realized in the improvement of malting barley varieties as a result of the collaborative efforts of state and federal research facilities and industry partners. Concurrently, there is always the need for new varieties that reduce the risk to the grower, provide improved quality characteristics to the end-user, and remain competitive with other crop options. Understanding the balance between pre-harvest sprouting and dormancy is an excellent example of such a need.