Seed germination, storability and moisture sorption isotherms of the endangered African rosewood (Pterocarpus erinaceus)

Abstract

African rosewood (Pterocarpus erinaceus) is an endemic, highly exploited and endangered tree species in arid and semi-arid zones of West Africa. Identifying optimum conditions for seed propagation and storage is critical for its conservation. This study assessed the effects of four pretreatments on seed germination and seedling vigour. Varying temperature, duration and packaging on storage deterioration were also evaluated for 12-months. Moisture sorption isotherms at 20, 25 and 30°C were characterized by equilibrating seed samples on series of lithium chloride (LiCl) solutions, generating relative humidity (RH) range of 3-95%. Data were fitted to four mathematical models; Chung Pfost, Halsey, Henderson and Oswin to determine the most suitable for describing the water activity (a w ), equilibrium moisture content (EMC) and temperature relationship. Results indicate that whole fruit sowing reduced germination capacity by more than 50% compared with extracted seeds at 5% probability level. Seeds stored at -10°C recorded the lowest rate of seed deterioration compared with ambient storage, regardless of packaging. Moisture sorption isotherms for rosewood showed a sigmoid (S-shaped) profile characteristic of orthodox seeds, and best described by the Henderson equation. Our findings highlight the need for adopting improved seed extraction technology and orthodox seed storage protocols for P. erinaceus conservation.

Temperature and soil nutrients drive seed traits variation in Pterocarpus erinaceus (African rosewood) in Ghana

“…Again, this is likely considering that African rosewood seeds are not associated with deep dormancy, and some studies suggest that the species do not require dormancy‐breaking treatments prior to sowing (Zida et al, 2005 ). Other studies have also reported low germination (Akpona et al, 2017 , several unpublished student theses and germination records at the NTSC), but see Amponsah et al ( 2022 ), Duvall ( 2008 ), Tiika et al ( 2019 ) and Zida et al ( 2005 ). Our results, however, show that significant differences exist among provenances.…”

“…The low‐seed shedding moisture of less than 12% obtained for all provenances is characteristic of seeds with orthodox storage behavior (Asomaning, 2018 ). Such seeds undergo maturation drying and can remain viable in ex‐situ storage over extended periods (Amponsah et al, 2022 ).…”

“…Again, reports on the germination capacity of African rosewood in literature are divergent. For instance, Amponsah et al ( 2022 ), Duvall ( 2008 ), and Tiika et al ( 2019 ) have reported high emergence of untreated seeds (above 70%) and pre‐treated seeds (between 70% and 100% with different pre‐treatment methods) in Ghana. On the contrary, experiments conducted in Burkina Faso and Ghana reported emergence of 70% and 50%, respectively (Kyei, 2016 ; Zida et al, 2005 ), while low germination of less than 50% in a separate study conducted in Benin have been reported with pre‐treated and untreated seeds (Akpona et al, 2017 ).…”