Factors controlling germination and dormancy processes in dimorphic fruits of Atriplex inflata (Chenopodiaceae)

Abstract

In some species belonging to the Asteraceae, Chenopodiaceae, Poaceae and Brassicaceae, a single individual produces different morphophysiological types of seeds that differ in colour, size, shape, germination and dormancy (Imbert 2002, Li et al. 2005, Mandak & Pysek 2005). This phenomenon is known as seed dimorphism or seed polymorphism. This may be an adaptive feature to harsh environments (Mandak 1997). In halophytic species, including Arthrocnemum, Atriplex, Chenopodium, Salicornia, Salsola, Spergularia and Suaeda, seed polymorphism is considered as an adaption to saline environments (Li et al. 2005). It enables halophytes to respond to severe conditions and could provide multiple opportunities for germination and growth in saline ecosystems (Song et al. 2007). It is well known that in halophytes, seeds are exposed to severe salinity at the soil surface; this is not suitable for germination and seedling establishment. Upon salt dilution by rain, germination is maximal for non dormant seeds (Ungar 1995, Debez et al. 2004). However, in saline biotopes, salinity is in permanent fluctuation and the re-increase of soil salinity prevents germination (Easton & Kleindorfer 2008) and in some cases, it induces a secondary dormancy, like in seeds of Suaeda aralocaspica (Wang et al. 2008). It is well known that many seeds are dormant at maturity. Baskin & Baskin (2004) define five classes of dormancy in seeds of Angiosperms. They include physiological dormancy, morphological dormancy, morphophysiological dormancy, physical dormancy and combined dormancy (physical and physiological dormancy). Several methods are used to break dormancy including physical and chemical treatments. These treatments are specific for each type of dormancy (Mandak & Pysek 2001). For instance, the mechanical and acid scarifications are largely used for physically dormant seeds