PhD defense: Max Herzog – Biologisk Institut - Københavns Universitet

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PhD defense: Max Herzog

Mechanisms of flood tolerance in wheat and rice - The role of leaf gas films during plant submergence.

Supervisor: Professor Ole Pedersen, BIO-UCPH

Assessment Committee 
Jens Borum (Chair), Freshwater Biological Laboratory, BIO-UCPH
Eric J. W. Visser, Inst. for Water and Wetland Res., Radboud University Nijmegen, NL
Margret Sauter, Botanical Institute, Kiel University, Germany                    

Abstract
Most crops are sensitive to excess water, and consequently floods have detrimental effects on crop yields worldwide. In addition, global climate change is expected to regionally increase the number of floods within decades, urging for more flood-tolerant crop cultivars to be released. The aim of this thesis was to assess mechanisms conferring rice (Oryza sativa) and wheat (Triticum aestivum) flood tolerance, focusing on the role of leaf gas films during plant submergence. Reviewing the literature showed that wheat germplasm holds genetic variation towards waterlogging (soil flooding), and highlighted traits such as improved internal aeration of the root system and short term anoxia tolerance of seminal roots as conferring tolerance. However, further work on especially anoxia tolerance and genotype × environment interactions is required in order to explore the available genetic resources. Experimental work assessed the physiologic, metabolomic and genetic response of wheat subjected to complete submergence, documenting contrasting submergence tolerance between two cultivars. Manipulating leaf gas film presence affected wheat and rice submergence tolerance such as plant growth and survival. However, leaf gas film retention times did not differ between 14 winter wheat cultivars. Due to the low genetic variation in wheat gas film retention times, a future prominent role of leaf gas films in improving (i) wheat submergence and (ii) rice salinity tolerance was not generally supported.

Pictures illustrating differential growth responses in wheat, rice, maize, soybean and/or their wild relatives upon flood treatments. a) Waterlogging-tolerant breeding-line (left) and commercial wheat variety (right) after 6 weeks of waterlogging 3 weeks after sowing. b) Submergence-tolerant wheat cultivar Swarna-sub1 (right) and intolerant cultivar Swarna (left) after 10 days of submergence. c) Flood-intolerant maize (left) compared to wild maize relative Zea nicaraguagensis (right) during a flood. d) Soybean (G. max, left) compared to wild relative (G. soja, right) upon flooding in University of Missouri field evaluations.