In situ fertility decline and provenance differences in the East African Yellow Wood ( Podocarpus falcatus) measured through in vitro seed germination

Abstract

Studies on changes in in situ fertility status, provenance differences, impact of storage time, as well as effects of biological, chemical and physical factors on propagule viability were conducted on Podocarpus falcatus (Thunb.) Mirb. (synonym P. gracilior Pilg.) through in vitro seed germination. Percentage germination was best at 25 °C and was significantly different ( P<0.001) from those at 20, 30 and 35 °C. Treating seeds with GA3 or GA4/7 (both at 10 −4 M) failed to significantly improve germination. Germination declined with storage time; and percentage germination of seeds stored at 1 °C for 24 months was as good as those stored at room temperature for 6 months. Percentage germination of seeds harvested in 1990 (maximum of 98%) was significantly different ( P<0.001) from those harvested in 1995 (maximum of 75%), 1998 (maximum of 60%) and 2000 (maximum of 61%). Also, seeds harvested in 1990 germinated more vigorously and uniformly than those harvested in the years 1995, 1998, and 2000. Percentage germination of three seed categories harvested from the same individual tree at three consecutive seasons was significantly different ( P<0.001). Seed provenances from central, south-eastern, southern and western Ethiopia showed significant differences in germination ( P<0.001) between each other. From these investigations, it is concluded that reproductive capacity of the species is rapidly declining, fertility of the tree varies from region to region, successful fruiting in the female tree is greatly influenced by such factors as climatic conditions and sexual dimorphism, and that sclerotesta dormancy is a serious limitation to the propagation of the species.