Association between leaf senescence dynamics and age-related yield decline in the perennial grain crop intermediate wheatgrass

Background and Aims Intermediate wheatgrass (Thinopyrum intermedium, IWG) is an emerging perennial grain currently being domesticated, but its adoption is constrained by a yield decline particularly between the 1st and the 2nd years, which basis is still poorly understood. Here, we hypothesized that this decline is primarily driven by shifts in senescence dynamics triggered by plant aging, leading to a limitation on photoassimilate remobilization towards seed filling in the second production year. Methods To test this hypothesis, we continuously measured senescence dynamics proxied by tracking photosynthetic rate along with leaf blade and sheath nitrogen content over two consecutive growing seasons, yielding up to 1080 observations. Additionally, we phenotyped stomatal anatomical traits associated with plant aging and we quantified grain yield and its component traits including seed mass, size, number and harvest index. Key Results An interannual yield decline of 23.4% was due to a reduction in seed mass but not in number of seeds or spikes, indicating a limitation of photoassimilate availability. Consistent with this, higher Year 1 yields were associated a delay of the onset of senescence by 421.4°Cd, with photosynthetic and leaf nitrogen decline rates that were 42% and 7 times steeper compared to Year 2. Leaf blade stomatal densities, size and nitrogen were lower in Year 2, consistent with lowering of leaf construction costs through aging. Conclusions These results show that IWG interannual yield decline an aging process that is correlated with a shift toward earlier and slower rate of canopy senescence that is possibly limiting the rate of nitrogen remobilization for seed filling. While further confirmation is needed, our results indicate that i) leaf nitrogen and stomatal anatomy could be potentially used as indirect selection traits and ii) genetic manipulation of leaf senescence is potentially a viable strategy for mitigating IWG interannual yield decline.