Seed germination of Opuntia stricta: Implications for management strategies in the Kruger National Park

Abstract

The declared alien invader, Opuntia stricta (Haw.) Haw., is a serious pest in parts of the eastern Cape, northern Cape, Kwazulu-Natal, and Mpumalanga (in particular the Kruger National Park). To help with the development of an effective management strategy for the weed in the Kruger National Park (KNP), research on its biology and ecology was initiated with a study on seed germination. Seeds isolated from unripe, medium-ripe or ripe fruit were incubated at 20/15°C, 30/20°C or 35/25°C (day/night regimes; 12/12 h cycles). Germination was negligible at 20/15°C, while the optimum regime was 30/20°C. Averaged across temperature at final count (day 22) there were no significant differences in germination between seed from the three fruit classes, viz. 45, 40 and 48% for unripe, medium-ripe and ripe fruit, respectively. Seeds not used in the initial experiment were stored at room temperature for one year before germination was tested at 30/20°C and 27/17°C temperature regimes. Storage increased germination significantly to 79, 89 and 82% for seed from unripe, medium-ripe and ripe fruit, respectively, and neither the temperature nor the fruit class effect was significant. Long-term weather data for Skukuza (KNP) indicate that November–March is probably the peak period for germination of O. stricta seed. Results also suggest that control measures should be instituted, and the plants preferably killed, before fruit set occurs.