Dormancy-breaking and germination requirements for seeds of Acacia papyrocarpa, Acacia oswaldii and Senna artemisioides ssp.×coriacea, three Australian arid-zone Fabaceae species

Abstract

Physical dormancy is common in seeds of arid-land legumes. Improved understanding of germination requirements of hard-seeded species will further our understanding of arid lands and aid restoration projects. We studied the germination responses of Acacia papyrocarpa (Benth.), A. oswaldii (F.Muell) and Senna artemisioides (Gaudich. ex DC.) Randell ssp. × coriacea (Benth.) Randell from a chenopod shrubland in South Australia. Imbibition testing indicated that all three species had physical dormancy, but the proportion of dormant seeds was lower in A. oswaldii. This corresponded to a thinner testa in this species. Mechanisms tested to scarify seeds included mechanical scarification and different durations of wet or dry heat. Mechanically scarified seeds germinated readily, reaching maximum numbers in 10–15 days, independently of incubation temperatures, with the exception of S. artemisioides seeds, which germinated at a slower rate in cooler temperatures. Overall, wet heat was more effective than dry heat to alleviate physical dormancy, whereas dry heat in some cases resulted in seed mortality. On the basis of these results, it is recommended that seeds of A. papyrocarpa and S. artemisoides be pretreated with wet heat in future restoration programs. No pre-treatment is required for dormancy loss in A. oswaldii seeds. The different responses of seeds of these species suggest that their populations have varying strategies for persistence in this unpredictable environment.

Markedly different patterns of imbibition in seeds of 48 Acacia species

“…Likewise, Pound et al . (2014) found that non-treated seeds of A. oswaldii had a gradual and ongoing germination response over time and in the present study some lenses of this species popped from just being on a moistened paper towel. As noted in Burrows et al .…”

“…Some studies of Caesalpinioideae and Mimosoideae species have related palisade thickness to water impermeability (e.g. Venier et al ., 2012; Pound et al ., 2014). The present study, in combination with Burrows et al .…”

“…While there have been numerous studies of germination in species of the Mimosoideae and Caesalpinioideae, few have specifically investigated the initial imbibition phase of the process (e.g. Clemens et al ., 1977; Wilson and Witkowski, 1998; Funes and Venier, 2006; Commander et al ., 2009; Venier et al ., 2012; Pound et al ., 2014; Matos et al ., 2015; Jaganathan et al ., 2017, 2018; Suleiman et al ., 2018). Most of these studies have been of control and mechanically scarified seeds over relatively short time frames (e.g.…”

Effect of Electrical Current Applied in Soaking Conditions on Germination of Acacia and Maize Seeds

“…Various artificial techniques have been used to successfully overcome physical dormancy in legumes such as acacia species. Some studies have shown that the highest germination percentages are obtained when seeds are submerged in boiling water before being planted (Walters et al, 2004;Rasebeka et al, 2014;Pound et al, 2014). Another practice that has been applied with good results in some crops (including maize) to increase germination is soaking the seeds for 10-25h in water, (Harris et al, 1999).…”

“…Physical dormancy is the water impermeability of seed coats and it has been suggested that variations in the seed coat structure among neotropical Acacia species could be related to different regenerative responses to environmental conditions (Venier et al, 2014). Overall, information on seed dormancy of arid zone species is limited and particularly based on Oceania's arid zone (Pound et al, 2014).…”