Swartzia langsdorffii Raddi: morphophysiological traits of a recalcitrant seed dispersed during the dry season

Abstract

Swartzia langsdorffii seeds have recalcitrant characteristics. Nonetheless, dispersal begins in the month with the lowest precipitation in the studied region, which could lead to seed death by desiccation. Therefore, the objectives of this study were: (1) to characterize the physiological behaviour of S. langsdorffii seeds related to their desiccation sensitivity/tolerance; and (2) to assess the morphophysiological characteristics that enable the seeds to remain viable after dispersal. Fruits and seeds were subjected to biometric evaluation and the anatomical and ultrastructural features of the seeds were determined. Field assessments were performed to determine the capacity of the seeds to maintain viability and to verify the relation between seed viability, diaspore water content and environmental variables. Seeds of this species were found to be recalcitrant and showed pores distributed throughout the seed coat, and contained a large number of stomata in the hypocotyl–radicle axis epidermis. Moreover, phenolic compounds were found throughout the radicle region. Seeds remained viable in the soil for up to 7 months after dispersal without a significant decrease in water content, despite the low precipitation and soil water content. Radicle protrusion began 5 months after dispersal and coincided with partial fruit decomposition at the beginning of the rainy season. Thus, the possible microclimate created by the pericarp, with the moisture content of the aril and the soil, the presence of the structures in the axis, such as the pores and stomata, the chemical composition and the morphology of S. langsdorffii seeds could favour maintenance of their viability until the beginning of the rainy season.

A new approach towards the so-called recalcitrant seeds

“…Among the groups that persist in the area, the panel that was demonstrated up to two decades ago did not change much afterward (Figure 1). The majority of the studies are basically focused on desiccation tolerance Corsato et al, 2012;Chapell et al, 2015;Amoedo and Ferraz, 2017;Gasparin et al, 2017;Subbiah et al, 2017;Chandra and Keshavkant, 2018;Plitta-Michalak et al, 2018), identification of storage behavior (Comin et al, 2014;Joshi et al, 2015;Vicente et al, 2016; 2017; Plitta-Michalak et al, 2018), analysis of deterioration and evaluation of techniques to extend the storage period (Barbedo and Cicero, 2000;Andréo et al, 2006;Bonjovani and Barbedo, 2008;Ballesteros et al, 2014;Lan et al, 2014;Parkhey et al, 2014;Garcia et al, 2015;Ming-Yue et al, 2015;Umarani et al, 2015;Araldi et al, 2016;Hossel et al, 2016;Félix et al, 2017), and rare studying other aspects such as seed maturation (Avila et al, 2009;Lamarca et al, 2013b;Mata et al, 2013;Schultz et al, 2014;Araldi and Coelho, 2015;Shibata and Coelho, 2016;Souza et al, 2018a, b), whose importance will be discussed later, and ecological (Ramlall et al, 2015;Vaz et al, 2016;Porto et al, 2018) or germinative aspects (Moothoo-Padayachie et al, 2016). An analysis, albeit superficial, of studies developed in Brazil and in the world shows small differences.…”

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

“…However, Vaz et al . () did not detect significant seed predation or removal during a field study with this species, nor did they observe any animal attempting to feed on the fruits or seeds. As a result intact fruits are dispersed containing seeds that remain viable in the soil for up to 7 months, including an aril and pericarp that do not have an obvious role, particularly the aril.…”

“…The trees produce large orange fruits containing one to six recalcitrant seeds with an aril, and all diaspore structures have a high water content at the time of dispersal (Vaz et al . ). Considering these traits, Martins et al .…”

“…Furthermore, S. langsdorffii diaspores are rich in secondary compounds such as tannins and saponins in the pericarp (Colpas & Oliveira ) and phenolic compounds in the seeds (Vaz et al . ). These secondary metabolites are known for their role in seed defence against herbivores and pathogens (Cipollini & Levey ) and, specifically saponins have a strong antinutrient role (Francis et al .…”

“…A large amount of seed coat pores and stomata in the embryo appear to aid gas exchange with the surroundings (Vaz et al . ), suggesting a suite of mechanisms involved in prolonged maintenance of seed viability. These features lead to the hypothesis that the S. langsdorffii pericarp and aril tissues play an important role in seed viability maintenance after dispersal, since the seeds are desiccation‐sensitive, dispersed in the dry season and retain viability until the rainy season begins (Vaz et al .…”