Irrigate for more seeds and heat for better germination in Australian
Choengsaat, D. Plummer, J. A. Turner, D. W.
Plant Sciences, Faculty of Agriculture, University of Western Australia, Nedlands, WA 6907, Australia.
Acta Horticulturae. 1998. 454: 241-250
CAB Abstract 980306730
Commercial development of the Australian daisies Rhodanthe chlorocephala subsp. rosea and Schoenia filifolia subsp. subulifolia [Helichrysum filifolium] is limited by seed dormancy. The effect of irrigation on plant growth and seed yield was examined in greenhouse and field experiments in Western Australia. Water deficit substantially reduced branching which limited the sites for terminal inflorescence production. This reduced seed yield. In a field experiment, irrigating to restore 25% of class A pan evaporation halved stem numbers and reduced seed yield to one-third compared with irrigating to restore 100% class A pan evaporation. The effect of irrigation on seed germinability was monitored from 3 to 6 months after harvest at storage temperatures of 5, 15, 25, 30, 40, 55 or 65 °C. R. chlorocephala seeds stored at 30 °C had 97% germination. High storage temperatures decreased seed germination to 90%. Dormancy in R. chlorocephala seeds increased with increasing irrigation rate but disappeared within 2 months of harvest. One month after harvest, 96% of S. filifolia seeds were viable and all seeds were dormant. Subsequent dormancy release depended on storage temperature. After 2 months' storage at 65 °C germination was 80% and this fell to 60% after 3 months' storage due to reduced viability. In contrast, seeds stored at 25, 30 or 40 °C had approximately 90% germination after 3 months' storage. Short term exposure of S. filifolia (1-14 days) to high temperature (65-105 °C ) were examined and exposure to 80 °C for 11-13 days overcame dormancy.