Coccoloba uvifera L. associated with Scleroderma Bermudense Coker: a pantropical ectomycorrhizal symbiosis used in restoring of degraded coastal sand dunes

Abstract

Coccoloba uvifera L. (Polygonacaeae), named also seagrape, is an ectomycorrhizal (ECM) Caribbean beach tree, introduced pantropically for stabilizing coastal soils and producing edible fruits. This review covers the pantropical distribution and micropropagation of seagrape as well as genetic diversity, functional traits and use of ECM symbioses in response to salinity, both in its native regions and areas where it has been introduced. The ECM fungal diversity associated with seagrape was found to be relatively low in its region of origin, with Scleroderma bermudense Coker being the predominant fungal species. In regions of introduction, seagrape predominantly associated with Scleroderma species, whereas S. bermudense was exclusively identified in Réunion and Senegal. The introduction of S. bermudense is likely through spores adhering to the seed coats of seagrape, suggesting a vertical transmission of ECM colonization in seagrape by S. bermudense. This ECM fungus demonstrated its capacity to enhance salt tolerance in seagrape seedlings by reducing Na concentration and increasing K and Ca levels, consequently promoting higher K/Na and Ca/Na ratios in the tissues of ECM seedlings vs. non-ECM plants in nursery conditions. Moreover, the ECM symbiosis positively influenced growth, photosynthetic and transpiration rates, chlorophyll fluorescence and content, stomatal conductance, intercellular CO₂, and water status, which improved the performance of ECM seagrape exposed to salt stress in planting conditions. The standardization of seagrape micropropagation emerges as a crucial tool for propagating homogeneous plant material in nursery and planting conditions. This review also explores the use of the ECM symbiosis between seagrape and S. bermudense as a strategy for restoring degraded coastal ecosystems in the Caribbean, Indian Ocean, and West African regions.

Keywords: Scleroderma bermudense; Genetic diversity; Micropropagation; Restoration; Salinity tolerance; Seagrape.

Fig. 1

Natural distribution of seagrape indicated by the shaded areas along the coasts of the Americas and the Caribbean islands (Parrotta 2000)

Fig. 2

Different stages in seagrape micropropagation. a, fresh branch used to prepare explants, b, shoot multiplication. c, rooting of shoots. d, hardening of plantlets in the greenhouse (Manokari et al. 2020)

Fig. 3

Seagrape fruits and Scleroderma bermudense spores from Bois Jolan (Guadeloupe). (a) Fresh and (b) dry seagrape fruit; (c) S. bermudense sporocarps, either semi-hypogeous and immature (red asterisks), or old and releasing spores (arrowheads), with a section of a young sporocarp displaying the violet immature spore mass; (d) S. bermudense spores in light microscopy; (e), (f) SEM of pericarp surface from a fruit covered by Scleroderma spores (arrowheads). Bars are 1 cm in (a-c); 10 μm in (d-f) (Séne et al. 2018)

Fig. 4

Distribution of ECM fungi associated with Coccoloba uvifera, C. swartzii and C. pubescens along a salinity gradient in Martinique and Guadeloupe (Bâ et al. 2014)