Trinexapac-Ethyl and Prohexadione-Calcium Effects on Seed Production and Quality in Grass and Forage Legume Seed Crops.

Trinexapac-ethyl (TE) and prohexadione-calcium (PC) are beneficial plant growth regulators (PGRs) that have been widely used in forage and turf seed crops.  These PGRs control lodging and increase seed yield through their effect on increasing seed number, but what about their effect on seed quality?  In perennial ryegrass (Lolium perenne L.), tall fescue [Schedonorus arundinaceus (Shreb.) Dumort.], creeping red fescue (Festuca rubra L. subsp. rubra) and Chewings fescue [F. rubra L. subsp. fallax (Thuill.) Nyman], seed weight was not affected by TE or PC across 23 field trials.  Seed weight was increased by TE in 5 trials and was reduced by TE and PC in 1 trial.  Seed germination and seedling weight were not affected in these species by TE or PC regardless of application rate.  Seed weight, germination, and seedling weight in perennial ryegrass were affected by the seed’s position of origin within the spikelet but not by application of TE.  In red clover seed crops (Trifolium pratense L.), seed yield was increased by TE but not by PC.  Seed number was increased by TE in red clover but unlike in grass seed crops, seed weight was reduced.  Best seed yields among TE rates tested were a trade-off between increased seed number and decreased seed weight.  Nevertheless, seed germination was not affected by applications of TE in red clover.  These PGRs are important seed production tools because they aid the grower in overcoming biological and economic inefficiencies and result in increased seed yield and profitability without affecting seed quality.