Impact on physiology and malting quality of barley exposed to heat, drought and their combination during different growth stages under controlled environment

Authors: Mahalingam, Ramamurthy; Bregitzer, Paul

Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2018
Publication Date: 2/1/2019
Citation: Mahalingam, R., Bregitzer, P.P. 2019. Impact on physiology and malting quality of barley exposed to heat, drought and their combination during different growth stages under controlled environment. Physiologia Plantarum. 165(2):277-289. https://doi.org/10.1111/ppl.12841
DOI: https://doi.org/10.1111/ppl.12841

Interpretive Summary: Drought and heat are two major abiotic stresses that negatively impact seed yield and quality. In barley, especially the quality of the seeds is a critical factor for the malting and brewing industries. Research on screening germplasm for heat and drought stress tolerance tend to use plants in the vegetative stage owing to short time for growing and for accommodating more number of plants. However, in barley like other cereals stress during post-anthesis is more detrimental. In this research we used four commercial two-row US spring barley varieties. Bowman is a feed variety, Conrad and Crystal are malt varieties while Garnet is a feed and malt variety. We subjected these lines to drought, heat and combined stress during vegetative stage and another batch of plants were subjected to these stresses during heading. Stress imposed during vegetative stage had no impact on final seed yields and malting quality. However, when the stressors were applied during heading stage significant reductions in yields were recorded. Barley in general are drought tolerant but are extremely sensitive to heat. When exposed to combined heat and drought all the four tested varieties showed more than 95% reduction in their yields. Significant differences in malt extract, protein content and b-glucan were observed when the stress was during heading. This suggests that new germplasm sources with tolerance to heat and combined heat and drought stress have to be introduced into the breeding programs to develop new varieties that can sustain the increase in global temperatures and water deficits predicted for the future.

Technical Abstract: Drought and heat stress are two major abiotic stresses that tend to co-occur in nature. Recent climate change models predict that frequency and duration of high temperatures and moisture deficits are on the rise and can be detrimental to crop production and hence a serious threat for global food security. In this study we examined the impact of short-term heat, drought and combined heat and drought stress on four barley varieties. These stresses were applied during vegetative stage or during heading stages. The impact on root, shoot biomass as well as yields was analyzed. This study demonstrated that short-term heat and drought stress during vegetative stages does not have any bearing on the yield outcomes. Heat and combined stress during heading led to drastic reduction in yields of all the four varieties. Micromalted seeds collected from plants stressed during heading showed differences in malt extract, beta-glucan content, and percent soluble protein. Screening barley germplasm during heading stage is recommended to identify novel sources of tolerance to combined stress. Apart from seed yield, assessing the seed quality traits of concern for the stakeholders and/or consumers should be an integral part of breeding programs for developing new varieties with improved heat and drought stress tolerance.