Abstract
Halopyrum mucronatum (L.) Stapf. (Poaceae) is a perennial halophyte grass dominating the coastal dune vegetation along Arabian sea coasts. This stoloniferous grass produces black and brown seeds (caryopses) during summer and winter, respectively. This study examined germination characteristics and sensitivity of two seed morphs to salinity (0,150 and 300 mM NaCl), thermoperiods (10/20, 15/25, 20/30 and 25/35˚C) and photoperiod (12-h photoperiod and 24-h dark) environments. Both seed morphs lacked innate dormancy and germinated maximally in distilled water. Cooler thermoperiod (10/20 ˚C) was most inhibitory for the germination of both seed morphs and their optimal germination occurred at warmer thermoperiod (25/35 ˚C). Under moderate to warmer thermoperiods, germination of both seed types decreased only in high (300 mM NaCl) salinity. Whereas at cooler thermoperiod, salinity increment led to a gradual decline in germination of both summer and winter seeds. In general, summer seeds were more tolerant to salinity than the winter seeds. Summer seeds also germinated to relatively higher percentage in dark under high salinity compared to winter seeds. In addition, summer seeds showed substantially lesser mean germination time under cooler thermoperiod than the brown seeds. This study unveils many similarities and differences in the germination characteristics and sensitivity patterns of two seed morphs.
