The effect of seed coat removal on seed germination of Terminalia superba Engl. & Diels | JBES 2021

Authors: Terminalia superba, Decoated seeds, Germination, Temperature, Germination media

Journal name: Journal of Biodiversity and Environmental Sciences | JBES

Publisher: International Network For Natural Sciences | INNSPUB

Abstract

The influence of four constant temperatures: 20°C, 25°C, 30°C, 35°C and three germination media: 1% water agar, heat sterilized river sand and seed testing paper (STP) on the germination of decoated seeds of Terminalia superba Engl. & Diels. were investigated. The germination media were placed in 90 mm diameter plastic Petri dishes with seventy five decoated seeds in 3 replicates of 25 seeds. The statistical design used in the investigation was a completely randomized design in a 3 x 4 factorial (germination media × incubation temperatures). Decoated seeds of T. superba germinated at all the four temperatures investigated. The optimum temperatures were determined as 25°C, 30°C and 35°C. All the three media can be considered ideal for the reason that these temperatures interacted with the germination media to record germination percentages ranging from 73 to 89% in the study. Mean germination time (MGT) was significantly (p < 0.001) shorter when agar was used as germination media compared to when germination was carried out on STP and soil. The shapes of germination curves describing the cumulative germination of decoated seeds of T. superba at all temperatures and on all the germination media investigated are S-shaped.

Introduction

Seed germination is controlled by several environmental factors, such as seed moisture content, temperature, and light. Seed condition also affects germination; for example, the seed coat may be water impermeable, or the mature seed may contain an underdeveloped embryo that only grows to full size after imbibition (Geneve, 2003). The seed coat represents a first line of defense against adverse external factors (helps protect the embryo from mechanical injury and from drying out) and also acts as channel for transmitting environmental cues to the interior of the seed (Radchuk and Borisjuk, 2014).

Integrity of seed coat surface is extremely important for seed quality and fitness during seed storage or germination, and diverse technologies are available for preserving and enhancing of seed surface (Black and Halmer, 2006; Brooker et al., 2007). That notwithstanding, an impermeable seed or fruit coat may impose physical dormancy which must be broken before water and air can reach the embryo and initiate germination (Baskin and Baskin, 2014). Most species have a seed coat which is impervious to water. This causes seed dormancy so that germination may extend over months or years. Example are the acacias and hence for their efficient germination at the nursery, it is necessary to apply some form of presowing treatment to ensure not only a high final germination percentage but rapid and uniform germination (Doran et al., 1983).

The seeds of Prunus yedoensis also have slow and poor germination when intact. Decoating their seeds shortens the mean germination time (MGT) and improves seed germination percentage significantly. (Hyun Kim, 2019). Decoated seeds of Syzygium cumini germinated faster than coated seeds under nursery conditions, with high significant germination percentages, dry matter production rates and vigor indices (Sivasubramaniam and Selvarani, 2012). Saeed and Thanos (2006) found seed coat to be inhibitory to the germination of Pinus gerardiana as removal of seed coat promoted both rate and final germination. Chika et al., 2020 reported that decoating seeds of Mansonia altissima improved their germination and resulted in the highest germination percentage. Bedada et al. (2018) also reported that de-coating improved germination and early nursery performance of Olea europaea.

Terminalia superba is one of the most heavily exploited African timber species, and locally, supplies have dwindled, with reports of declining populations in Côte d’Ivoire, Ghana, Nigeria, Cameroon and Congo (FAO,1984; N’Sosso, 1990). In Ghana, T. superba was one of the priority species earmarked for planting during the National Forest Plantation Development Programme launched in the year 2002. It is also on the list of priority species being planted under the on-going Ghana Forest Investment Programme. These developments have resulted in the need for sufficient quantities of good quality seeds to meet planting targets. Cobbinah et al. (2001) and NTSC (2008) have reported days to first germination as 16 and 23 days respectively for seeds of T. superba sown intact. Unlike T. ivorensis, no serious dormancy problem has been reported about T. superba. However, pre- treatment methods such as nicking or soaking in water have been recommended for faster and even germination (TTSA, 2010). This study investigated the response of decoated seeds (seed with testa or seed coat removed) of T. superba to different temperatures and various germination media. Get the full articles by following the link The effect of seed coat removal on seed germination of Terminalia superba Engl. & Diels