Alleviation of salinity stress and the response to temperature in two seed morphs of Halopyrum mucronatum (Poaceae)

Abstract

Halopyrum mucronatum (L.) Stapf. is a coastal dune grass that produces seeds twice during each growing season. Seeds produced during May (summer seed) were black and heavier (2.8 0.09 mg) than brown seeds (2.1 0.04 mg; winter seed) that were produced in November. There was greater than 95% germination in both seed morphs in the non-saline controls at all temperature regimes, but germination was inhibited more by low than high temperatures in the salinity treatments. Summer seeds were more tolerant of salinity than the winter seeds. Highest germination was obtained in all salinity treatments at a 20/30˚C (12-h night/12-h day) temperature regime for the winter seeds and at 25/35˚C for the summer seeds. Gibberellic acid, thiourea and nitrate partially alleviated the effects of salinity in summer seeds and gibberellic acid, kinetin and betaine were able to alleviate the inhibitory effects of salinity on the germination of winter seeds. The seeds of Halopyrum mucronatum exhibited seed dimorphism and a difference in physiological response in the two seed morphs, which could provide them with multiple opportunities to germinate and establish in the hot, dry, saline and unpredictable maritime coastal-dune environment along the Arabian Sea coast of Karachi, Pakistan.