Conditions for Optimum Germination of Sprawling Bauhinia Seed (Tylosema Fassoglense) (Kotschy Ex Schweinf.) Torre & Hillc

Abstract

Understanding seed biology and germination ecology of plants is critical for domestication of neglected and underutilized species (NUS). However, this information is not readily available for Tylosema fassoglense [Family: Fabaceae]; despite its potential as a future crop. This research is primarily intended to benefit small-holder farmers of Kenya, by improving nutrition and enhancing sustainable agriculture, while contributing to good health and well-being. The main objective of this study was to evaluate the seed germination requirements of T. fassoglense by determining dormancy type, the effects of light, temperature and water potential on germination of scarified seeds as well as assessing the correlations among seed functional traits. Seed lots of T. fassoglense were collected from Busia, Migori and Siaya counties in Kenya. Seed dormancy was determined by water imbibition rates and germination tests on scarified and non-scarified. Scarified seeds were germinated under 12/12 plus 0/24 hour photoperiod as well as over a range of temperatures from 10 to 45 °C with intervals of 5 °C and at varied water potentials; 0, -0.25, -0.5, -1.0, -1.5 Megapascal (MPa). Water imbibition rates (g), germination percentages as well seed mass, oil and morphology were measured. Percentage data were normalized by arcsine transformation, subjected to analysis of variance (ANOVA) and the means separated with Tukey’s HSD (p<0.05) using SAS Version 2002-2003 statistical software. Scarification significantly (p<0.05) improved water uptake by 4 to 22 times as well as germination percentage from 30% to 90% (Migori seed lot) and from 70% to ≥90% (both Busia and Siaya seed lots). Seeds germinated well under light/dark or dark photoperiods while relative light germination index (RLG) ranged from 0.46 to 0.57. Seed germination was significantly (p<0.05) reduced at 10 °C and 40 °C whilst germination was zero at 45 °C in all the seed lots. The calculated base, optimum and ceiling temperatures (Tb, To and Tc; 50th percentile) ranges were 4.05-8.0 °C, 33.61-35.75 °C and 46.54-47.24 °C respectively while thermal time (θT(50)) suboptimal ranged from 76.19 to 89.02 degree Celsius days (°C d). Low water potential of -0.5 MPa significantly (p<0.05) reduced final germination to less than 50% in all seed lots while germination was zero at both -1.0 and -1.5 MPa. The base water potential (Ψb) and hydro time (θH(20)) ranges was -0.92 to -0.97 MPa and 3.95- xiii 4.11 Megapascal days (MPa d) respectively. Siaya seed lot were significantly (p<0.05) heavier than the other lots. Negatively significant (p<0.05) correlations were observed between Tb and θT; Ψb and θT while non-significant correlations were observed between germination and physical traits. Scarification improved water imbibition as well as final germination percentage and seeds of T. fassoglense are probably neutral photoblastic. The optimum temperature range for germination was 30-35 °C while seed germination was tolerant to low water potential up to -0.5 MPa. There were interrelationships among seed functional traits of T. fassoglense. The findings of this study will be useful in future research contributing towards the domestication of T. fassoglense as a future crop to enhance a sustainable agriculture and nutrition in Kenya and potentially worldwide. Keywords: dormancy; germination; light; potential crop; physical traits; temperature; Tylosema fassoglense; water potential