Germination responses of Terminalia superba Engl. and diels seeds on the 2-way Grant's thermogradient plate

Abstract

The goal of the study was to take a more comprehensive look at germination responses of the species to a broad range of alternating or constant temperatures on the thermogradient plate. Terminalia superba seeds were placed in Petri dishes containing a gel of 1% agar for germination over a period of 30 consecutive days. Petri dishes were arranged 8×8 units on the 2-way Grant's thermogradient plate (a bi-directional incubator). The instrument allows for germination testing of seeds over a wide range of single temperature and alternating temperature regimes over a time continuum, given 64 temperature combinations (regimes) (5 to 40°C). Conditions were 40/40°C (day/night temperature) on the high end of the plate and 5/5 °C (day/night temperature) on the cool end. Dried out agar in petri dishes located at the hot end of the plate were replaced periodically. Two temperature gradients ranging from 5 to 40°C were used. The first gradient, progressing from left to right on the thermogradient plate in dark, was alternated every 12 h with the second progressing from front to back of the thermogradient plate with light. The study was repeated two times. Twenty seeds were used in each replication. The various temperature combinations had significant effect on final germination percentage, mean germination time, time for first germination and rate of germination. Alternating temperatures improved overall germination. The best germination at a constant temperature was at 35/35°C (88%). The best temperature combinations for seed germination at alternating temperatures were 35/40°C (100%); 35/15°C(95%); 40/25°C(95%); 20/40°C (92.5%) and 40/30°C (92.5%). © 2011 Academic Journals Inc.