Abstract
Carob (Ceratonia siliqua L.) is a relevant element of the Mediterranean spontaneous vegetation. Moreover, it is useful in reforestation, and it is currently re-valued for sustainable agriculture in dryland areas. However, the difficulties tied to carob propagation (mainly seed dormancy) hamper its large-scale cultivation. In this paper, the effects of four seed treatments (no treatment [control], soaking at 70 °C and 90 °C in water, or in 96% sulphuric acid) on five carob genotypes germination were studied. As compared to the very low germination of untreated seeds (0–13% germination), sulphuric acid (93–100% germination) and 90 °C water soaking (from 72 to > 90% germination in four out the five genotypes) were effective in promoting germination. Soaking at 90 °C resulted in the leaching of a higher amount of total polyphenols from the genotypes seed coat as compared to soaking at 70 °C. A significant correlation (0.75**) was ascertained between polyphenol leaching of the different genotypes and germination. These results suggest that dormancy in this species is not primarily associated with seed coat hardness, as it is generally thought, but also with the release of polyphenols. Polyphenols determination of the dormant and the few non-dormant seeds of the different genotypes also seem to confirm this hypothesis since these last showed an almost halved total polyphenols content (on average 17.0) as compared to dormant ones (34.8 mg g−1 of seed FW). Further studies may determine the polyphenols involved, but also assess new, easier to carry out, seed treatments. The important role of the galactomannans on seed germination of carob is also discussed. Finally, similar studies may enhance the knowledge of dormancy processes in other Fabaceae species whose germination is positively affected by hot water treatments.
Highlights
Seed dormancy is commonly considered as the inability of a viable seed to germinate under suitable environmental conditions
The effects of different scarification treatments and the role of carob seed polyphenols on germination of five carob genotypes collected in Sicily (Italy) were discussed
Sulphuric acid and hot water treatments were very effective in improving carob seed germination
Summary
Seed dormancy is commonly considered as the inability of a viable seed to germinate under suitable environmental conditions. It is an important ecological feature, since the scattering of germination overtime permits some species to survive when unfavorable environmental conditions occur, damaging the portion of readily germinable seeds (Baskin and Baskin 2014). Dormancy linked to waterproofness of the seed coat (physical dormancy according to Baskin and Baskin 2004) affects several families of angiosperms and many members of the Fabaceae family Due to the capability to fix nitrogen (N), the Fabaceae species exert an important role within the wild plant community, and as crops for sustainable agriculture. The comprehension of the dormancy processes associated with their germination is important
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