Seed Germination Characteristics of Three Woody Plant Species from South Texas

Abstract

The seed germination of blackbursh (Acacia rigidula), guajillo (Acacia berlandieri), and guayacan (Porlieria angustifolia) was investigated in relation to temperature and various regimes of light; substrate salinity, pH, and osmotic potential; seed age; and site of seed source. Germination of blackbrush seed is restricted by an impermeable seed coat. Mechanical scarification or soaking seeds in concentrated sulfuric acid for 15 to 30 min increased blackbrush germination from 74 to 86%. Blackbrush, guajillo, and guayacan seed germination was best at about 25 degrees C. Blackbrush seed germination was not reduced by alternating as opposed to constant temperatures but germination of guajillo and guayacan was generally lower under alternating temperatures. Light was not required for germination. No seed dormancy mechanisms were observed other than the hard seed coat of blackbrush, and seed viability was not significantly reduced after 1 year in storage at room conditions. Guajillo seed collected from plants growing on a sandy loam site had higher percent germination than those of plants growing on a more droughtly clay loam site. Germination of blackbrush and guayacan from different sites did not differ. Germination and radicle length of seedlings were relatively tolerant of extremes of pH. Guajillo germination was significantly reduced in a aqueous solution of 2,500 ppm NaCl. Germination of blackbrush seed was not affected by 10,000 ppm NaCl, but guayacan seed germination was reduced at this concentration. Radicle lengths of seedlings of all species were significantly reduced at 10,000 ppm NaCl. Seed germination and radicle length of all 3 species were progressively decreased by increasing moisture stress up to -12 bars. Emergence of blackbrush and guajillo seedlings was not dependent upon burial in the soil; germination and emergence were greatest on the soil surface or from a depth of 1 cm.