Monocarpic senescence is a complex quantitative trait, under tight genetic and environmental control, whereupon nutrients become remobilised into grain. Delayed senescence, or ‘staygreen’ traits have been shown to harbour agronomic potential, enhancing stress tolerance and nitrogen use efficiency (NUE). Genetics underpinning senescence are largely unknown, with phenotypes under strong environmental influence, requiring intensive phenotyping and are therefore difficult to select.

A three-year NUE screen of Triticum aestivum cv. Paragon EMS mutant lines, identified two high-yielding lines with environmentally stable, functional, staygreen phenotypes, and differential nitrogen responses. For each mutant near isogenic lines (NILs), segregating for the staygreen phenotype were developed, via Single Seed Descent (SSD), for trait mapping purposes, and populations trialled under field conditions from 2016-2018.

Can a delay in senescence, as per these staygreens, extend grain fill duration to increase final grain weights? If so, does this come at the expense of other yield components? A trade-off which must be considered when deploying staygreen traits in breeding. We conducted grain filling experiments on the staygreen parents and cv. Paragon and witnessed a significant extension in grain fill duration. Grain filling profiles mirrored their respective senescence phenotypes, with potentially positive effects, dependent on agronomic conditions.

To map the staygreen trait we converted complex, quantitative senescence phenotypes, into qualitative staygreen, nonstaygreen classifications through derivation of senescence metrics from multi-year trial data. This approach facilitated bulk segregant analysis, which was performed using exome capture, the analysis of which reveals distinct, independent, loci for each staygreen. We have fine mapped each region through development of genetic markers and further utilisation of the NIL populations, permitting identification of gene candidates underpinning these staygreen phenotypes.

Furthermore, through conducting multi-year multi-environment trials we have attempted to match these staygreens with their target environment. In combination not only do our results provide an improved understanding of senescence regulation in wheat, but realise the potential of the staygreen trait in breeding.