A role for fruit structure in seed survival and germination of Swartzia langsdorffii Raddi beyond dispersal

Abstract

Diaspore structure has been hypothesised to play a role in seed viability and/or germination of recalcitrant seeds, especially for Swartzia langsdorffii. Thus, this work aims to (i) investigate the in situ contribution of pericarp and aril on seed viability and germination, and (ii) identify morphoanatomical traits of S. langsdorffii diaspores that allow its desiccation-sensitive seeds to remain viable. The role of the pericarp and aril in seed survival and germination was investigated by placing the whole fruit, whole seeds (arillate seed) and bare seeds (without aril) in soil in the forest understorey, assessing germination, emergence, dead, firm and predated seeds, and water content of pericarps, arils and seeds. Correlation analysis was performed between environmental variables and physiological parameters. Histochemical features of diaspores were also investigated. Pericarp water content fell after several months, while the aril maintained its water content. Seeds did not lose water even without the presence of the pericarp and aril. However, presence of the pericarp promoted seed water content, viability and germination long after dispersal. The embryo had a thickened outer periclinal cell wall. Pericarp and aril are not essential to prevent water loss in seeds, but do help to retain seed moisture, favouring viability maintenance and promoting germination during the rainy season. Morphoanatomical features of seeds are suggested as main factors that reduce water loss. Survival of these desiccation-sensitive seeds upon dispersal during the dry season appears to be facilitated by multiple diaspore features that prevent viability loss.

Effect of temperature and drought stress on germination of Magnolia pugana, an endangered species from western Mexico

“…Various authors have reported different viability percentages in Magnolia species: 78 % for M. iltisiana (Saldaña-Acosta et al 2001), 100 % for M. dealbata (Corral-Aguirre & Sánchez-Velásquez 2006), 80 % for M. schiedeana (Vásquez-Morales & Sánchez-Velásquez 2011), 92 and 87.5 % for M. perezfarrerae and M. sharpii, respectively (Vásquez-Morales & Ramírez-Marcial 2019). Habitat characteristics, longevity during storage, seed moisture content, and the morpho-anatomical features of recalcitrant seeds explain this variability (Ibrahim & Roberts 1983, Vaz et al 2018. Our main conclusion in this experimental study on the effect of increased temperature and drought stress on the germination of Magnolia pugana seeds is that the interaction of simulated drought and temperature increases affected decreasing germination percentages and delaying the mean germination time.…”

Sugar Receding in Aril Benefits the Recalcitrant Seeds of Litchi (Litchi chinensis) and Longan (Dimocarpus longan) to Cope with Dry Spells after Maturation

“…The arils of litchis and longans evolved from the funicle of the ovule after fertilization. So far, many studies have shown that, in addition to the rewards for seed dispersers [27,28], the arils have multiple roles, including protection of the seeds from water loss and regulation of seed germination time to enhance survival under unfavorable weather conditions [20,30]. Here, we suggest that, in litchi and longan fruits, arils evolved not just for providing means for seed dispersal like fleshy fruit but also for other physiological roles due to their water-rich [20] and sugar-rich features for the purpose of germination and seedling establishment.…”

“…Evrard [29] reported that the presence of the aril lowered the seed germination rate of Afzelia bipindensis, for the aril may contain growth inhibitors such as flavonoids, which are necessary to temporarily promote seed longevity. Our previous and other studies have reported that the pericarp and aril could help to retain seed moisture and favor viability maintenance of these seeds in the dry spells of the wet season [20,30]. In litchi and longan fruits, whether the sugar-rich arils and the "sugar receding" of arils can modulate the seed germination vigor during unpredictable dry weather is unknown.…”