Seed Germination Characteristics of Two Woody Legumes (Retama and Twisted Acacia) from South Texas

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Abstract
The seed germination characteristics of retama (P. aculeata) and twisted acacia (A. schaffneri) [both species, but especially Acacia are undesirable brush species] were invesigtated in relation to temperature and light regimes, substrate salinity, pH, osmotic potential, seed age and seedling emergence. Seed germination of both species is restricted by impermeable seed coats. Soaking seeds of both species in concentrated sulfuric acid for 45 min increased germination. Retama seed germination was .gtoreq. 87% at continous temperatures of 15.degree.-35.degree. C and at alternating temperatures of 10.degree.-20.degree., 15.degree.-25.degree. and 20.degree.-30.degree. C, while twisted acacia seed germination was .gtoreq. 58% at constant temperatures of 15.degree.-30.degree. C, and at alternating temperatures of 10.degree.-20.degree., 15.degree.-25.degree. and 20.degree.-30.degree. C. Light was not required for germination and no dormancy mechanisms were observed. Viability of twisted acacia and retama seeds was not reduced after storage at room conditions for 2 yr. Germination and radicle length were sensitive to osmotic potentials of polyethylene glycol soltuions of 0.4 MPa [mega pascal] and no germination occurred at 1.4 MPa. Germination of both species was only mildly depressed in aqueous solutions of 10 g/l NaCl; however, radicle elongation of both species was reduced at 5 g/l NaCl and severely inhibited at 10 g/l NaCl. The osmotic potentials of the NaCl solutions had little effect on germination, but they may have contributed to reduced radicle growth. Percent germination and seedling radicle length of both species were relatively tolerant of pH extreme. Twisted acacia seedling emergence was highest when the seeds were left exposed on the soil surface, whereas optimum retama seedling emergence occurred when seeds were covered with 1-7 cm of soil.