Shirin Sharifiamina1, Ali Shayanfar2, Derrick J Moot1, Mark Bloomberg3
1Field Service Centre, 3Agribusiness and Commerce, Lincoln University, PO Box 85084, Lincoln 7647, New Zealand
2Plant production, Gorgan University of Agricultural and Natural Resources, Gorgan, Iran
We investigated sub clover germination responses to different combinations of constant temperature (T) and water potential (WP) under laboratory conditions. Seeds of sub clover ‘Napier’ were incubated in the dark in combinations of T = 5, 10, 15, 20, 25, 30 and 35°C; and WP = 0, -0.18, -0.37, -0.63 and -0.95 MPa. Seed germination was monitored every 8 hours for the first 4 days, then inspected every 24 hours for 14 days. Results were analysed in graphical form. Maximum or near-maximum percent germination (GP) occurred over a broad range of T (15-25°C) under moist conditions. However, the optimal temperature range for GP was markedly narrowed when WP was -0.63 MPa and -0.95MPa. In contrast to GP, optimum median germination rate (GR(50)) occurred over a much narrower range for both T and WP, reaching a maximum at 30°C and 0 MPa, and declining more-or-less linearly with decreasing T and WP. The optimal temperature for GR(50) appeared to interact with WP so that it occurred at 30°C for WP= 0, -0.18 and -0.37 MPa, but at 25°C for -0.63 MPa. At the maximum T in this experiment (35°C), GR(50) declined from the optimal rate but was still quite rapid under zero or mild WP stress. Therefore it was not possible to identify a ceiling temperature where GR(50) was zero, under these moist conditions. Implications of these results for field germination of sub clover are discussed.