Stratification in switchgrass seeds is reversed and hastened by drying

Switchgrass (Panicum virgatum L.) seed dormancy is a major obstacle to successful establishment of this multi-purpose species. We have investigated the influences of prolonged stratification, poststratification drying, restratification, and afterripening on germinability of 'Cave-in-Rock' switchgrass seeds. Germination can be increased many-fold to greater than or equal to80% with 14 d of stratification, if the seeds are moved directly to germination without drying. However, we have round germinabitity (but not viability) may decrease by half or more if the stratified seeds are first dried and then rehydrated for germination testing. The reappearance of dormancy (secondary dormancy) during poststratification drying is herein called reversion. During poststratification drying, dormancy reversion increased as the degree of desiccation increased. Extended stratification (for greater than or equal to42 d) prevented reversion. Afterripening also reduced the potential for reversion. Stratification and afterripening appeared to work additively to remove revertibility. Restratifying dried seeds showed that, while a drying interruption caused reversion, it also decreased the dormancy variability within a seedlot and shortened the total stratification time needed to obtain maximum germination compared with continuous stratification. Switchgrass seeds can be moved toward greater germinability by stratification, but drying following insufficient stratification can lead to dormancy reversion.