Role of Dormancy Regulating Chemicals in Alleviating the Seed Germination of Three Playa Halophytes

The effects of dormancy regulating chemicals [nitrate, thiourea, proline, kinetin and gibberellin (GA3)] were tested on the seed germination of three salt playa halophytes, Halogeton glomeratus, Lepidium latifolium, and Peganum harmala under various salinity treatments (0 to 400 mM NaCl) and photoperiod regimes (12/12 h light/dark and 24 h dark). More than 80% of all seed species germinate under non-saline conditions in a 12/12 h light/dark photoperiod. However, there was a progressive increase in the enforced dormancy with an increase in salinity treatments. Thiourea substantially improved seed germination and the rate of germination of all test species under saline conditions. Kinetin partially alleviated the salinity effect on the seed germination of H. glomeratus and P. harmala but not for L. latifolium. GA3 substantially improved the seed germination in L. latifolium. Nitrate and proline had no effect under saline conditions. Seed germination was completely inhibited in L. latifolium, partially in P. harmala, but had no effect on H. glomeratus seeds when germinated in the dark. GA3 alleviated dark inhibition in the order: L. latifolium > P. harmala > H. glomeratus. Species specific responses to GA3 and kinetin and environmentally mediated responses of thiourea appear to influence the seed germination of the salt playa species.