GERMINATION OF PERENNIAL RYEGRASS AND ANNUAL BLUEGRASS SEEDS SUBJECTED TO HYDRATION-DEHYDRATION CYCLES

Seeds that encounter widely fluctuating water conditions during germination could die, become dormant, lose hydration-dependent steps toward radicle emergence through dehydration, or incrementally accumulate events required for radicle emergence. These alternatives were evaluated with seeds of perennial ryegrass (Lolium perenne L.) and annual bluegrass (Poa annua L. var. annua) exposed to repeated hydration-dehydration episodes. Seeds were cycled between liquid (hydration phase, psi = 0 MPa)and vapor (dehydration phase, psi = - 4 or - 10 MPa) environments for up to 16.5 cycles or 328 h, with phase durations of 8, 16, or 24 h. Cycling generally resulted in delayed, but more uniform germination. Cycled seeds required fewer hours in contact with liquid water to germinate than did continuously hydrated seeds and were not killed by repeated dehydration for up to 24 h at - 10 MPa. Coleorhiza tissue that emerged from perennial ryegrass seeds following accumulation of 24 hydration-phase hours retracted during dehydration, but this did not negatively affect radicle emergence upon subsequent rehydration. Annual bluegrass seeds were prevented from germinating by 8-h hydration phases coupled with 16- or 24-h dehydration phases at - 10 MPa. Upon transfer to continuous hydration, however, seeds germinated within 36 h. These data support the hypothesis that seeds of perennial ryegrass and annual bluegrass can progress toward germination with intermittent hydration.