Polyphenols leaching and seed dormancy in carob (Ceratonia siliqua L.) in relation to hot water treatment

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.

Overcoming seed coat–imposed dormancy in wild species of Cajanus and Rhynchosia

“…Several studies report different pretreatments effective in removing hard seeds in legumes. Sulfuric acid scarification is reported to be the best treatment in overcoming hard seeds and improving germination in carob ( Ceratonia siliqua L.) (Cavallaro et al., 2021), Vigna spp. (Wang et al., 2007), and Onobrychis species (Majidi & Barati, 2011).…”

“…The seed coat of Fabaceae constitutes of a single palisade layer of packed and elongated sclereids and nonuniformly thickened cell wall. Cuticle or waxy deposition, lignin, tannin, lipids, phenolics, callose, suberin, pigmentation etc are associated with hardseededness in legumes (Cavallaro et al, 2021;Lamichaney et al, 2017;Smykal et al, 2014). Remanandan et al (1991) reported the hardseededness to vary from 0% to 71% in pigeon pea.…”

“…The wild species of pigeon pea are a great source of numerous traits but for its efficient utilization, successful germination is a prerequisite. In legumes, like pigeon pea, physical dormancy in the form of hardseededness is the most prevalent type of seed dormancy (Cavallaro et al., 2021; Singh et al., 2020). The hard seed prevents entry of water into the seed, thereby restricts the metabolic function essential for germination to occur.…”

“…The hard seed prevents entry of water into the seed, thereby restricts the metabolic function essential for germination to occur. However, the dormancy in legumes is not only associated with hardseededness but also with the polyphenols present in the seed coat (Cavallaro et al., 2021), removal of which following hot water treatment enhanced germination of Ceratonia siliqua L. The lack of information on overcoming hardseededness of these wild accessions creates a problem and is a bottleneck during its conservation and utilization. Therefore, an efficient and effective technique for removing hardseededness of these species must be developed as a considerable inter‐ and intraspecific variation for seed dormancy exists (Mira et al., 2017; Singh et al., 2020).…”

Overcoming seed coat imposed dormancy in wild species of pigeonpea (Cajanus cajan L. Millsp.)

“…of forty-four accessions used in the experiment. [1] C. scarabaeoides,[2] C. crassus,[3] C. cajanifolius,[4] R. minima,[5] R. bracteata, [6] R. rothii,[7] R. rufescens, [8] R. aurea,[9] C. lineatus,[10] C. platycarpus…”