DIFFERENTIAL GERMINATION BY DIMORPHIC ACHENES OF YELLOW STARTHISTLE (CENTAUREA-SOLSTITIALIS L.) UNDER WATER-STRESS

Yellow starthistle germination in an environmental chamber was 74, 38, 3, and 0% at osmotic potentials of 0, -0.5, -1.0, and -1.5 MPa, respe ctively. Salinity levels of 0, 4, 8, and 12 dSm(-1) had an inconsisten t effect on germination. The presence of a pappus (p-achene) was assoc iated with an 11 and 15% increase in germination over those achenes wi thout a pappus (np-achene) at 0 and -1.5 MPa, respectively. Field germ ination of p-achenes was 29 and 33% greater than np-achenes at La Gran de, OR and Walla Walla, WA, respectively. Total germination (field plu s lab) was not influenced by time of burial (3 months) or 1- and 2-cm burial depths. Dimorphic achenes appear to be associated with success in exploiting highly variable soil moisture regimes in semi-arid envir onments. (C) 1997 Academic Press Limited.