Progress in Developing Kernza Wheatgrass As a Perennial Grain.

Kernza wheatgrass (Thinopyrum intermedium) is a perennial grain crop currently being developed. Over the last nine years, four cycles of mass selection primarily based on seed yield per head and seed mass have been performed. The population resulting from two cycles of selection has been evaluated in multiple years and locations. Under irrigation, yields in the second year were increased by 77% after two cycles of selection. With drought conditions and no irrigation, seed production of all populations was near zero.

The highest yield obtained from clones selected for yield and grown in small plots under irrigation in Kansas has been 1130 kg ha^-1. In contrast, clones selected for seed mass in Kansas have produced 2160 kg ha^-1 in Minnesota without irrigation. Due to consistently higher seed yields in northern climates, high temperatures during grain filling is the working hypothesis for limited grain yield in southern locations.

Biomass yield in small plots grown in Kansas (with irrigation) and Minnesota has been 18 to 20 Mg ha^-1. Harvest index in these plots was 6 to 9%. High biomass production coupled with comparably low seed yield highlights the importance of increasing harvest index as a breeding objective.

Seed mass of kernza is currently small, only about 15% of wheat. Therefore, seed size is a major limitation to use of the crop and a primary breeding objective. Seed mass has been less responsive to selection than yield, increasing by only 23% in response to two cycles of selection. Individual clones have had seed mass 90% greater than the starting population. Therefore, breeding strategies that take advantage of non-additive genetic effects may be required.   

In conclusion, improved breeding methods, refined agronomic techniques, and production in cooler climates are expected to produce rapid increases in seed yield and seed mass of kernza.