Gamma irradiation induces sterility or seedlessness in black wattle (Acacia mearnsii)

Gamma irradiation of black wattle seed was tested to induce sterility in order to curb the spread of black wattle outside plantation boundaries. Initially, percentage germination (incubator and nursery), average root length after three days, seedling height at 30 days for treatments 0, 10, 20, 40, 60, 80, 100, 150, 200, 250, 300, 350, 400, 450, 500, 800, 1000. 1500, 2000, 2500, 5000, 10000 Gy were determined. Germination (%) under incubator conditions was high (88 to 99%) for 0 to 5000 Gy, but dropped to 5% at 10000 Gy. Germination (%) after 30 days in the nursery dropped from 80% to 5% from 400 to 1500 Gy. Root growth under incubator conditions ranged between 17 and 20 mm for 0 to 350 Gy, while from 400 to 5000 Gy it dropped from 15.25 to 4.48 mm. Seedling height after 30 days, although erratic, ranged from 14.49 to 21.50 mm at 0 to 100 Gy and from 150 to 1500 Gy it ranged from 12.00 to 14.19 rum. Seed was then irradiated (0, 350, 380, 400, 420, 450, 480, 500, 520, 550, 600 Gy), nursery sown and established as a field trial. Two months after planting, 100% survival was recorded for most treatments. After four months, survival decreased above 420 Gy. Height (one and three year measurements) fluctuated over 2 m and dbh (two and three year measurements) over 2.5 m. Flowering showed significant reduction in number of trees flowering (% flowering) and degree of flowering between 400 and 520 Gy. Seed set was significantly reduced between 350 and 520 Gy. Between 350 and 520 Gy, growth traits were acceptable to the control and allowed for sufficient seed reduction.