The relationship between ions, vigour and salinity tolerance of Acacia seeds

Seeds of A. bivenosa DC. Prod., A. coriacea DC., A. elata A. Cunn. Ex Benth., A. farnesiana (L.) Willd., A. nilotica Willd. ex Del., A. salicina Lindl., A. saligna (Labill.) H. Wendle., A. senegal (L.) Willd., A. tortilis (Forsk.) Hayne and A. tumida F. Muell. ex Benth. were tested for their final germination percentage (FG) in distilled water (DW) and in 25-400 mol m(-3) NaCl, germination rate (1/t(50), where t(50) is the time to 50% of final germination in DW), Ca and K concentration (Ca-unt, K-unt), the leakage of these ions when soaked for 24 h in DW (Ca-DW, K-DW) and the leakage (additional to that in DW) when soaked in 250 mol m(-3) NaCl (Ca-NaCl, K-NaCl). Linear regression revealed significant positive relationships between salinity tolerance (I-50, the concentration of NaCl required to reduce final germination to 50% of the control value in DW) and FG, Rate, Ca-unt/K-unt and Ca(NaC)l/K-NaCl. There was also a significant negative relationship between I-50 and K-unt. Multiple regression equations were developed to predict I-50 from the above parameters. Equations based on (1) FG and Rate, (2) Ca-unt and K-unt, and (3) any of these four factors, accounted for 61, 60 and 79%, respectively, of the variation in I-50. Further equations, introducing the leakage of ions into DW and NaCl and the ratios of ion concentrations monitored, improved the predictive value of the equation. The best equation, accounting for 93% of the variation was: I-50 = 108 + 422 Rate - 1.32 K-unt + 16.3 Ca-DW - 5.4 K-DW + 71.6 K/Ca-DW. These equations provide a screening test for salt tolerance of Acacia seed germination based on simple and rapid laboratory chemical analyses and germination tests.