Field evaluation of transgenic wheat expressing a modified ADP-glucose pyrophosphorylase large subunit

Wheat yield is influenced by the efficacy of seed starch biosynthetic enzymes. ADP-glucose pyrophosphorylase (AGP) catalyzes a ratelimiting step in seed starch biosynthesis. We transformed the hard spring wheat (Triticum aestivum L.) cultivar Hi-Line with a modified maize AGP large subunit sequence (Sh2r6hs) to increase AGP activity. In previously described growth chamber studies, Sh2r6hs conditioned increased AGP activity, seed yield, and plant size. The primary objective of this study was to determine whether a similar yield enhancement could be detected under field conditions. Sh2r6hs transgenies were field tested over four growing years, in three locations, with varying planting density and irrigation. The results indicate that significant yield increases were more likely to occur in space-planted, irrigated environments than densely planted, rainfed environments, suggesting that limited abiotic resources may subsequently limit Sh2r6hs-associated yield enhancement. In elite lines, as in the F-2-derived trials in which tissue culture derived mutations were reduced by out-crossing, Sh2r6hs appears to confer a yield advantage only when field conditions are nonlimiting.