Seed germination and seedling establishement at different sowing depths of selected medicinal woody plant species, Uganda

Abstract

Seed germination and seedling establishment behavior of wild medicinal woody plant species under cultivation are not fully known. Yet, cultivation provides an opportunity for ex situ conservation of threatened medicinal woody plant species. This study investigated the germination and growth responses of four wild medicinal woody plant species; Albizia coriaria Welw. Ex Oliv, Prunus Africana (Hook.f.) Kalkm, Warbugia ugandensis Sprague and Hoslundia opposite Vahl, to enhance their cultivation outside the wild. The objectives were to (i) compare the germination of selected medicinal plant species at different sowing depths (ii) analyze the survival and mortality of seedlings of the selected medicinal plant species (iii) evaluate biomass allocation in the selected medicinal plant species at different sowing depths. The experiment was conducted under greenhouse conditions inMasoli, Gayaza and Wakiso district. The seeds were sown in a standard soil mixture at three sowing depths of 0, 3, 6 cm and watered daily for 100 days. Germinability, Mean germination time, coefficient of variation with time, mean germination rate, uncertainty, synchrony, seedling survival and biomass allocation were investigated. Kruskal-Wallis test was used to compare mean ranks of germination measurements between treatments. X2 was used to test for the association between seedling survival and sowing depth. Spearman’s rank correlation coefficient was used to correlate biomass between the root and the shoot. One-way Analysis of Variance was used to compare root to shoot ratio at different sowing depth. The highest germinability was recorded at 0 cm sowing depth. W. ugandensis indicated the highest germinability. A.coriaria took the shortest time to germinate while P. Africana, the longest time. At 0 cm sowing depth, seeds of all species tended to germinate earlier. Seeds of A. coriaria showed higher germination vigour than the other seeds. Germination in P. Africana was more synchronized than in either A. coriaria or W. ugandensis. Survival and sowing depth were not associated, but A. coriaria showed a significantly higher survival percentage (P=0.021) than W. ugandensis with lowest survival percentage. Root biomass strongly correlated with shoot biomass, r=0.84, r2=0.72. Root to shoot biomass ratio was significantly higher (p=0.021) at 6 cm sowing depth. Therefore, sowing seeds at shallow soil depth resulted in comparably higher seed germinability, asynchronized germination and higher shoot biomass. Therefore, this study recommends sowing within a profile of not more than 3 cm deeper for these species.