Influence of different temperatures on seedling growth and development of Calobota sericea, a semi-arid rangeland species of South Africa

This study determined how temperature affected the early growth of seedlings of Calobota sericea (Thunb.) Boatwr. & B.-E.van Wyk. One-month-old C. sericea seedlings were grown at constant temperatures of 2.5, 5, 10 and 20 degrees C for 30 days. After 30 days the plants were removed and shoot length, root length, stem thickness, number of leaves, middle leaflet length, leaf width, petiole length, shoot fresh and dry mass, and cell membrane stability through electrolyte leakage from the leaves, and shoot water content were measured. Results showed that the optimum temperature for C. sericea seedling growth was approximately 10 degrees C. Significant seedling mortality was observed at 20 degrees C, while no mortality was observed between 2.5 and 5 degrees C, and less than 4% of seedlings died at 10 degrees C. The majority of measured morphological variables in this study increased significantly from 2.5 degrees C and 5 degrees C, reaching a maximum at 10 degrees C before decreasing significantly at 20 degrees C. Electrolyte leakage from leaves was significantly more at 2.5 degrees C and at 20 degrees C, suggesting that seedlings were more stressed at these temperatures. In conclusion, even though C. sericea has a wide optimum germination temperature range, early seedling growth requires a narrow temperature range for optimum growth and development.