Determination and equilibration of seed moisture content (SMC) and seed storage of black wattle (Acacia mearnsii) seed for gamma irradiation

Black wattle (Acacia mearnsii), a commercially grown forestry tree in South Africa, is now grown primarily for its pulping properties. However, black wattle is also considered an invader species of indigenous vegetation. Currently gamma irradiation techniques are being investigated as a means of producing a sterile or seedless variety. Various environmental factors enhance the effectiveness of irradiation techniques, two of which are, seed moisture content (SMC) and post-irradiation storage conditions. The SMC content of black wattle was determined to be 6.76 +/- 0.23% (percentage dry weight of original sample). Efforts to try and decrease and increase the natural SMC using desiccators containing lithium chloride, silica and glycerol (100 and 85%) were unsuccessful. Natural SMC of black wattle seeds is low enough for maximum irradiation damage to occur. Four post-irradiation storage conditions, seeds stored in sealed and unsealed bags in growth chambers, anoxic and oxic conditions, were examined through viability and growth studies. All four storage conditions did not significantly (p > 0.01) affect the performance of the irradiated seed when compared to the control. This suggests that prior to gamma irradiation, seed should be maintained under constant storage conditions of room temperatures between 18 and 24 degrees C in moisture-tight containers for approximately two weeks.