Germination response to temperature and water potential for Sprawling bauhinia (Tylosema fassoglense), a potential crop for Kenya

Abstract

The knowledge of cardinal temperatures is critical for understanding environmental tolerance limits for germinating plant species. However, this information is not readily available for Tylosema fassoglense [Family: Fabaceae]; despite its potential as a future crop to improve nutrition and enhance sustainable agriculture in Kenya.The objective of this study was to characterise seed germination responses to temperature and water potential of seed lots of T. fassoglenseseeds collected from three counties in Kenya; namely Busia, Migori and Siaya.Scarified seeds were germinated at a wide range of constant temperatures from 10 to 45 °C with intervals of 5 °C and water potentials from 0, -0.25, -0.5, -1.0, -1.5 Megepascal (MPa) at 25 °C.Seeds of T. fassoglense had a wide range of germination temperature of 20 °C (from 15 to 35 °C). Low (10 °C) and high (≥40 °C) temperatures significantly reduced germination in the three seed lots. Busia seed lot had the lowest final germination of 5% at 10 °C while germination was zero at 45 °C in all the seed lots tested. The calculated base, optimal and ceiling temperature (Tb, To and Tc) ranges were 4.05 - 8.0 °C; 33.61 - 35.75 °C; and 46.54 - 47.24 °C, respectively. Suboptimal and supraoptimal thermal time (θT(50)) ranged between 76.19 – 89.02 degree celcius days (°C d) and 30.3–41.89 °C d respectively. Water potential of -0.5 MPa significantly 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)) was between -0.92 to -0.97 MPa and 3.95–4.11 Megapascal days (MPad) respectively.The optimum temperature range for germination was 30–35 °C and seeds were tolerant to low water potential up to -0.5 MPa. However, further studies will need to be carried out on germination in the supraoptimal temperature range and water potential between 0 and -1.0 MPa. The findings in this study will be useful in future research contributing towards domestication of T. fassoglense.