Development of Physiological and Genetic Markers for Waterlogging Tolerance In Wheat.

Waterlogging is a primary constraint to wheat production in the soft winter wheat growing region of the Eastern United States.  In Arkansas, where moderate waterlogging during stand establishment occurs on a yearly basis, yield losses up to 33% have been observed.  Despite the adoption of agronomic practices such as drain furrows, waterlogging remains a constraint and genetic improvement is vital to increase the rate of yield gain in wheat.  It is also predicted that global climate change will result in increased winter precipitation and waterlogging of cereals.  Waterlogging causes an ‘energy crises’ due to low ATP production resulting from the inhibition of respiration and is often accompanied by element toxicity.  This results in poor root establishment, decreased stand and biomass, and senescence.  An underdeveloped root system may also reduce tolerance to late season heat and drought stress.  Tolerance mechanisms include formation of root arenchyma, stem elongation, and tolerance to element toxicity, resulting in a stay-green phenotype and more biomass for yield production.  The soft winter wheat breeding programs of the Southeastern U.S. (collectively known as SUNGRAINS) provide the only published source of waterlogging tolerant germplasm among the U.S. programs.  It is our charge to use this germplasm to dissect the physiology and genetics of waterlogging tolerance in wheat, with a focus on the vegetative stage.  To accomplish this, two waterlogging tolerant lines, Jaypee (Arkansas) and GA971127 (Georgia) will be used as model phenotypes. 

In the current study, the waterlogging tolerance of 15 wheat cultivars and Arkansas breeding lines was assessed using a greenhouse waterlogging protocol where wheat seedlings were waterlogged for 18 days starting at 21 days after emergence.  Traits measured weekly included chlorophyll fluorescence, quantum efficiency, chlorophyll (SPAD) and plant height.  Spectral reflectance was also measured using a handheld spectroradiometer (HandHeld 2, ASDI Boulder, CO) in the 300-1100nm range.  Following waterlogging both root and above ground biomass were harvested, weighed and reweighed following drying.  Significant differences were observed between treatments and cultivars for most traits with the largest differences measured for chlorophyll content, root biomass and above ground biomass.  A strong positive correlation was observed between quantum yield and chlorophyll content under waterlogging stress.  The waterlogging tolerant line Jaypee showed significantly higher root and above ground biomass accumulation under waterlogging compared to most cultivars.  USG3209 was among the most susceptible waterlogging genotypes with large reductions observed for chlorophyll, photosynthetic traits and root and vegetative biomass.  Based on these results, the USG3209/Jaypee WheatCAP mapping population was screened for waterlogging tolerance using similar methodology.  Data from this study are currently being used to map putative QTL for waterlogging tolerance and for developing spectral reflectance indices that can be used for screening germplasm for waterlogging tolerance.  Future studies will incorporate screening for waterlogging and element toxicity tolerance under field conditions.