Germination rate of annual bluegrass (Poa annua L.) seeds formed at different seasons

Abstract

Annual bluegrass (Poa annua L.) which derived from a putting green (GR) and an orchard (OR) was grown under field conditions from Sep., 2014 to May, 2015. GR and OR produced ripened seeds in Nov., 2014, Mar., Apr., May, 2015 and in Nov., Dec., 2014, Mar, Apr., May, 2015, respectively. Thousand grain weight (TGW), percentage of living seeds (PLS), germination rate in the incubator (GRI) and germination rate in the field (GRF) of the living seeds were measured in each times mentioned above. PLS of both GR and OR were higher than about 90%, regardless of times. The minimum and maximum values of the TGW were reached in May and Mar., 2015, respectively. The GRI values of GR (39.5±7.5% to 84.0±4.2%) were higher than those of OR (0% to 0.6±0.4%). On the other hand, GRF of GR was less than GRI, and the seed of OR was rarely germinated under field conditions. These results suggest that seed dormancy of GR is not so strong as compared to that of OR and the seed is possibly shifted to a primary, secondary and/or enforced dormancy depending on the environmental conditions.