Assessment of Seed Vigour Tests for Efficiently Determining the Physiological Potential of Tetrapleura tetraptera (Schum. & Thonn.)

Abstract

Seed vigour tests were conducted to identify differences in physiological potential among seed lots of Tetrapleura tetraptera (Schum. & Thonn.) with the potential to perform well after sowing and/or during storage. The present study aimed at investigating rapid vigour testing methods for estimating the relative physiological potential of T. tetraptera (Schum. & Thonn.) to provide relevant information to guide its domestication and ex-situ conservation. Eight (8) seed lots of T. tetraptera were subjected to the accelerated ageing and the electrical conductivity tests to determine their physiological potential. For the accelerated ageing tests, the traditional accelerated ageing (TAA) and the salt-saturated accelerated ageing (SSAA) tests were performed. In the TAA tests, seed lots were exposed to 100% RH at 38 and 41°C for 48, 72 and 96 h, respectively. In the SSAA tests, seed lots were exposed to saturated NaCl solution with RH of 76% at temperatures and durations similar to the TAA tests. For the electrical conductivity tests, leachates conductivity of the 8 seed lots, were measured after 20 seeds of each lot had been placed in beakers and soaked in 50 ml of de-ionized water for 1,2,3,4,5,6, and 24 h at room temperature (24-28°C). Seed moisture content was determined and seed germination tests of seed lots were conducted before and after the accelerated ageing tests. Seedling root, shoot and total length as well as seedling dry weights were also recorded after accelerated ageing and germination of the seeds. The experimental design was 8 x 7 factorial (lots x soaking period) for the conductivity test and 8 x 2 x 3 factorial (lots x temperature x exposure time) for the accelerated ageing tests, in a completely randomized design. Results showed that seed emergence and seedling length were effective to distinguish the physiological quality of T. tetraptera seeds while seedling dry weights were not. Accelerated ageing test influenced the percentage of germination, but showed low sensitivity in lots differentiation. For the electrical conductivity test, 24 h was the most promising soaking period for effective stratification in determining the physiological quality of T. tetrapteraseed lots and was significantly correlated with seed emergence (-0.76, p < 0.01) and seedling length (r = -0.72, p < 0.01). Electrical conductivity test may therefore be a more feasible option for vigour testing of T. tetraptera seeds.