Floret site utilization and reproductive tiller number are primary components of grain yield in intermediate wheatgrass spaced plants

Perennial plants provide extensive environmental services and increasing their prevalence on the agricultural landscape is one way to improve sustainability. Direct domestication of intermediate wheatgrass [Thinopyrum intermedium (Host) Barkworth & D.R. Dewey] as a perennial grain crop is underway, and selection has focused primarily on improving seed size and grain yield. Breeders lack understanding of grain yield and its relationship with component traits in this species. We characterized a large (n = 1,168) spaced plant nursery in St. Paul, MN, and Salina, KS, in 2017 and 2018 for a series of 13 yield component traits. In Year 2 in St. Paul, yield per plant and reproductive tiller number nearly doubled, whereas other yield components, including yield per spike, spikelets per spike, florets per spikelet, and thousand-grain weight, significantly decreased. Correlation analyses between traits highlighted positive associations of seven traits with grain yield. Structural equation modeling (SEM) revealed that when yield was measured on a yield per spike basis, floret site utilization was the primary contributor to yield, and when measured on a per-plant basis, reproductive tiller number was the primary contributor. The indirect effects of biomass and maturity traits on both measures of yield were limited. Future work should investigate the predictive ability of reproductive tiller counts in spaced plant and sward environments to inform how breeders assess and select for yield.

Automated summary

The study characterized yield component traits of intermediate wheatgrass and found positive correlations between certain traits and grain yield. Structural equation modeling revealed different primary contributors to yield under different measurement standards. Future research should focus on the predictive ability of reproductive tiller counts in assessing yield.