Abstract

BI Nyoka, GW Sileshi and SN Silim

Gliricidia sepium is an important species in tropical agroforestry systems where it is grown as a multipurpose tree species. The species is generally propagated from seed and stem cuttings. Establishment from seed is hampered by seed shortages as seed yields are very low on most sites. Gliricidia flowers profusely but pod and seed set are very low and this is attributed to high levels of flower and pod abortion. The objective of this study was to determine the level of flower and pod abortion in gliricidia, and contrast it with other related forest tree species. Sixty trees were randomly selected in two seedling seed orchards located at two sites: 30 trees each at Makoka and Chitedze Research Stations. Five racemes (with floral buds) per tree were randomly selected and tagged. The floral buds were monitored every two days to record the number of opened flowers and developing pods until all the tagged floral buds had opened and developed into mature pods or aborted. A high proportion (93%) of the trees completely aborted all their reproductive structures at Chitedze compared to only 6% at Makoka, making the former site less favourable for seed production compared to the latter. Overall, less than 3% of the flowers initiated in gliricidia produced pods, the rest were dropped. The observed level of abortion is not unusual as it is largely comparable to other related forest tree species of the Fabaceae family. Seed producers could improve seed yields in gliricidia by establishing seed orchards on appropriate sites and also using some seed sources with inherently high seed yield potential.