Production and handling of seeds of acacia xanthophloea brachystegia spiciformis and trachylobium verrucosum

Abstract

The current information available on the seed production processes of Acacia xanthophloea Benth. Brachystegia spiciformis Benth. and Trachylobium verrucosum (Gaertn.) Olivo is.limited to botanical description and generalities. The general reproductive development of A. xanthophloea was investigated in the Kibwezi Forest and that of ~. spiciformis and !. verrucosum in the Arabuko-Sokoke Forest in Kenya. Acacia xanthophloea had two flowering periods per year. These were synchronized with relatively dry periods. The other species flowered only once per year, but flowering was again synchronized with the single relatively dry period in that vicinity. Fruits of all three species developed during wetter periods and dried to maturity in somewhat drier periods. Developing fruits of all three species were eaten by baboons. The legumes of ~. xanthophloe~ and !. verrucosum were indehiscent, wh8reas ~nos~ of B. spicifo~m~G dehisced explosively. Fruits were collected from trees in the stands under study, and seeds extracted by hand. The seeds of all three species had thick, hard seedcoats, as is common for leguminous trees. Samples of seeds of each species were pretreated in 13 ways to determine whether germination could be enhanced. Seeds of ~. spiciformis germinated best without pretreatment (control) and thus seedcoats were not impermeable to water. Pretreatments, except nicking the seeds at the micropylar end, were not effective. Seeds of ~. xanthophloea and !. verrucosum had water-impermeable seedcoats. Impermeability was overcome by nicking the seeds. Other effective pretreatments were three hot-water pretreatments of varying duration and pretreatment for 32 min in concentrated sulphuric acid for A. xanthophloea, and for 32 min' and 16 min in concentrated sulphuric acid for T. verrucosum. Cutting tests of nongerminated seeds showed that most of !. verrucosum and A. xanthophloea were apparently still viable, but those of ~. spiciformis were dead. X-ray analysis showed that 0.3% of T. verrucosum, 10% of A. xanthophloea and 40% of B. spiciformis seeds had damaged embryos. The damage was caused by insect or by fungal and/or bacterial infection.