Heteromorphic Seed Germination and Seedling Emergence in the Legume Teramnus Labialis (L.F.) Spreng (Fabacaeae)
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Botany Heteromorphic seed germination and seedling emergence in the legume Teramnus labialis (L.f.) Spreng (Fabacaeae) Journal: Botany Manuscript ID cjb-2020-0008.R1 Manuscript Type: Article Date Submitted by the 17-Feb-2020 Author: Complete List of Authors: Acosta, Yanier; University of Ciego de Avila Pérez, Lianny; University of Ciego de Avila Escalante, Doris; University of Ciego de Avila Pérez, Aurora; University of Ciego de Avila Martínez-Montero,Draft Marcos; University of Ciego de Avila Fontes, Dayamí; University of Ciego de Avila Ahmed, Lina; INRA Sershen, Sershen; University of KwaZulu-Natal Lorenzo, José; University of Ciego de Avila, Lab for Plant Breeding and Conservation of Genetic Resources Keyword: animal feed, legumes, seed color, seed dormancy Is the invited manuscript for consideration in a Special Not applicable (regular submission) Issue? : https://mc06.manuscriptcentral.com/botany-pubs Page 1 of 28 Botany 1 Heteromorphic seed germination and seedling emergence in the legume Teramnus 2 labialis (L.f.) Spreng (Fabacaeae) 3 Yanier Acosta1 • Lianny Pérez2 • Doris Escalante2 • Aurora Pérez2 • Marcos Edel 4 Martínez-Montero2 • Dayamí Fontes1 • Lina Qadir Ahmed3,4 • Sershen5 • José Carlos 5 Lorenzo2,* 6 1 Faculty of Agricultural Sciences; 2 Laboratory for Plant Breeding & Conservation of 7 Genetic Resources, Bioplant Center; University of Ciego de Avila, Cuba. 8 3 INRA, UR4 P3F, Unité Pluridisciplinaire Pairies et Plantes Fourragères, Le Chêne - 9 BP 6, F-86600 Lusignan, France 10 4 Department of Field Crops, CollegeDraft of Agriculture, University of Salahaddin, Kirkuk 11 road, 44001 Erbil, Iraq 12 5 Department for Biodiversity and Conservation Biology, University of the Western 13 Cape, Private Bag X17, Bellville, 7535, South Africa 14 * To whom correspondence should be addressed: [email protected] 15 1 https://mc06.manuscriptcentral.com/botany-pubs Botany Page 2 of 28 16 Abstract 17 Seed heteromorphism can influence germination and ultimately seedling establishment, 18 particularly in disturbed habitats. This study compared seed and seedling traits across 19 three distinctly colored seed morphs (viz. light-brown, brown and dark-brown) of the 20 forage legume, Teramnus labialis. Brown seeds were of the best quality (i.e. un- 21 parasitized, filled and un-cracked): 389.3 quality seeds per 1000 units compared with 22 <270/1000 units for the other two morphs. Length, width, volume and water content 23 were lowest in light-brown and highest in dark-brown seeds. Seed thickness and mass 24 were lower in light-brown seeds. Dark-brown seeds imbibed fastest from 2 h onwards. 25 Germination was comparable across morphs after 7 d but lowest in light-brown (17% at 26 21 d) and highest in dark-brown (36%Draft at 21 d) seeds at 14 and 21 d. At 7 d, seedling 27 emergence in dark-brown (15.0%) seeds was higher than in the other two morphs (4- 28 6%); this remained so at 14 and 21 d. Seedling growth (number of leaves, stem height 29 and diameter, and root length) was superior in dark-brown seeds. Seed heteromorphism 30 in T. labialis may allow its persistence in disturbed habitats and dark-brown seeds are 31 best suited for seeding in revegetation projects, given their superior germination 32 capacity and seedling vigor. 33 Keywords: animal feed; crops; legumes; nitrogen fixation; seed color; seed dormancy. 34 Introduction 35 Over the last few decades seed heteromorphism, which involves the production of seeds 36 of different morphologies and/or germination behavior on different parts of the same 37 plant, has been reported in an increasing number of species (Imbert 2002; Lu et al. 2 https://mc06.manuscriptcentral.com/botany-pubs Page 3 of 28 Botany 38 2010; Gul et al. 2013; Bhatt and Santo 2016; Hughes 2018). The trait appears to be an 39 adaptation to habitat spatio-temporal variability (Venable et al. 1998; Liu et al. 2018; 40 Ma et al. 2018; Nisar et al. 2019). It can be “cryptic”, i.e. where seed types display 41 different ecological behaviors but no obvious morphological differences (Venable 1985) 42 but in many cases heteromorphism includes variation in seed size, which in turn 43 influences the timing and success of germination, and seedling establishment and 44 survival (Simons and Johnston 2006). When seed size variability influences germination 45 and is fixed through adaptation, the strategy can function as ‘bet-hedging’, where the 46 species brings about a reduction in short-term reproductive success in order to ensure 47 long-term risk reduction (Venable 2007; Matsuo et al. 2016); avoids the negative effects 48 of sib competition (Cheplick 1992) or density (Sadeh et al. 2009) or spreads the risk 49 among many offspring phenotypesDraft (Simons 2011). Importantly, seed heteromorphism 50 often allows a species differential germination behavior and ultimately seedling success, 51 particularly in disturbed habitats (Leverett and Jolls 2014). 52 Seed heteromorphism appears to be confined to representatives of a limited 53 number (n=18) of phylogenetically advanced angiosperm families, in particular the 54 Poaceae, Asteraceae, Chenopodiaceae and Brassicaceae (Imbert 2002). Differences 55 among seed morphs are generally based on one or more of the following: color, size, 56 morphology/anatomy, dispersal syndrome, dormancy and germination (Baskin and 57 Baskin 1998; Volis 2016; Dello Jacovo et al. 2019). The trait has also been reported in a 58 few members of the Fabacaeae (e.g. Amphicarpaea bracteata (Trapp 1988)) and most 59 recently Dello Jacovo et al. (2019) showed that the legume Lathyrus linifolius produces 60 heteromorphic seeds that can be distinguished by differences in seed color; however, the 61 two seed morphs displayed the same germination capacity. Characterizing the 62 phenomenon of seed heteromorphism in legumes is particularly important given the 3 https://mc06.manuscriptcentral.com/botany-pubs Botany Page 4 of 28 63 critical role(s) many members of the family play in agriculture, not only as a source of 64 carbohydrates and proteins for animals and humans but also as nitrogen fixers in 65 different ecosystems (Crews et al. 2016). For example, a rich diversity of legumes, e.g. 66 the genera Neonotonia, Teramnus, Stylosanthes, Centrosema and Macroptilium (Díaz et 67 al. 2012), are gaining popularity as a cover crops in diverse agricultural systems 68 (Mazorra-Calero et al. 2016), including fruit orchards (Grusak 2008). 69 Legumes such as Teramnus labialis (Fabaceae (alt. Leguminosae) tribe) have 70 been shown to be useful in mixed-agricultural systems (Borroto et al. 2007) and can be 71 particularly valuable for sustaining agro-ecosystems and restoring habitats by increasing 72 soil fertility and facilitating the establishment of other species (Acharya et al. 2006; 73 Mondoni et al. 2013). Seeds areDraft essential for these activities, particularly for 74 revegetation of degraded habitats or abandoned agricultural land), However, the use of 75 legume seeds can be problematic due to seed coat-imposed dormancy and/or highly 76 variable germination (Barker et al. 1977; Yuan 2017). The use of T. labialis for 77 example, is far from being maximized owing largely to low seed production, small seed 78 size and highly variable and low germination percentages, most likely due to physical 79 dormancy (González and Mendoza 1991; Acosta et al. 2019). 80 Physical dormancy in legumes is based on the presence of one or more water- 81 impermeable palisade cell layers in the seed coat (Baskin and Baskin 1998). Under 82 natural conditions, the seed coat becomes permeable by weathering or sloughing 83 through the action of one or more environmental factors, but this can take several 84 weeks, to months, which delays the germination and establishment of such species 85 (Smýkal et al. 2014). Researchers and farmers have developed a series of techniques to 86 make dormant seeds permeable, including mechanical scarification, and treatments with 87 sulfuric acid, enzymes, organic solvents, high atmospheric pressures, hot water, dry 4 https://mc06.manuscriptcentral.com/botany-pubs Page 5 of 28 Botany 88 storage and low temperatures (Baskin and Baskin 1998; Acosta et al. 2019). The 89 success of these dormancy breaking techniques is challenged by the fact that 90 heteromorphic seeds from a single plant may display a combination of different 91 germination strategies (which can be ‘opportunistic’ or ‘cautious’) (Venable 1985). A 92 field study on the dimorphic seeds of Atriplex prostrata and Salicornia europaea for 93 example, showed that germination was > 90% for large seeds of both species but much 94 lower (>50% and >75%, respectively) for small seeds (Carter and Ungar 2003). 95 During our previous study on T. labialis (Acosta et al. 2019), in which we 96 showed how cryostorage enhances subsequent plant productivity in the forage species, 97 we observed that this species exhibits seed color heterogeneity which is a common 98 indicator of seed heteromorphism.Draft Despite its potential as a cover crop in mixed 99 agricultural systems and value as a potential forage/cover crop for revegetating 100 degraded habitats, there are no published reports on seed heteromorphism in the species. 101 This motivated the present study, which aimed to investigate seed heteromorphism in T. 102 labialis via a comparison of three distinctly colored seed morphs (light-brown, brown 103 and dark-brown) that are produced on the same plant in this species. The specific 104 objectives of the study were as follows: 105 To compare the three seed morphs in terms of physical characteristics; 106 To compare the three seed morphs in terms of imbibition rate and 107 germination capacity; 108 To compare seedling emergence and growth across the three seed 109 morphs. 110 Materials and methods 5 https://mc06.manuscriptcentral.com/botany-pubs Botany Page 6 of 28 111 Plant material: In February 2018 seeds were collected from open pods of 50 randomly 112 selected mature plants belonging to one typical population in Ciego de Avila, Cuba 113 (21.99°06’85” N, 78.76°73’00”W, area sampled = 12 m2).