Germination and recovery responses of heteromorphic seeds of two co-occurring Arthrocnemum species to salinity, temperature and light

Arthrocnemum macrostachyum and A. indicum are succulent halophytes found in the coastal marshes of southern Pakistan and many other countries, where they act as primary producers and also have many potential economic usages. They produce large quantities of heteromorphic seeds every year. Many aspects of the seed biology of these congeneric plants are not known. This comparative study was conducted to determine the germination and subsequent recovery of ungerminated seeds on distilled water of heteromorphic seeds of these halophytes to salinity (0, 200, 400, 600, 800 and 1000 mM NaCl), thermoperiod (15/25, 20/30 and 25/35 °C), photoperiod (12 h light/12 h dark and 24 h dark) and their interactions. Seeds of A. macrostachyum were of two colors (i.e. black and brown), while seeds of A. indicum differed in size (i.e. small and large). Seeds of the two species lacked primary/innate dormancy and germinated quickly in distilled water at low to moderate thermoperiods, while 25/35 °C was more inhibitory. Seeds were positively photoblastic and failed to germinate in dark. Seeds of A. macrostachyum showed higher tolerance to salinity (germinating at 600 mM NaCl, equivalent to sea water salinity) than those of A. indicum (not germinating above 400 mM NaCl). Germination of black but not brown seeds of A. macrostachyum was higher in 200 mM NaCl compared to control at 25/35 °C. Whereas in case of A. indicum, large seeds showed higher germination in distilled water than small seeds but were sensitive to salinity. Ungerminated seeds from high salinity and dark, when transferred to distilled water and 12 h photoperiod respectively, showed recovery of germination. Hence, our data indicate many similarities and differences in the germination responses of heteromorphic seeds of A. macrostachyum and A. indicum.