The germination of milkweedvine (Morrenia odorataLindl. ♯3MONOD) seed at 20 or 25 C was unaffected by a 12-h photoperiod. The 12-h photoperiod, however, decreased germination by 50% at 15 C. No germination occurred at 35 C regardless of photoperiod. By alternating 35 C for 12 h with 20 C for 12 h, the germination percentage was 57%. Seedling growth was maximum at alternating temperatures of 30/20 C. Optimum pH for germination and seedling growth was 7 and germination did not occur at pH levels below 6. Seed germination declined steadily at osmotic stress below −0.12 MPa; no germination occurred at −0.5 MPa. Seedling growth was not influenced by osmotic stress down to −0.18 MPa. Germination percentages of seeds kept under aerated water and nonaerated water were similar, but the seedling growth was greater in aerated water. Seedling emergence was maximum from depths of 0.5 to 2.5 cm, but no seedling emerged from 0 or 10 cm. Planting depth was negatively correlated (r = −0.7) with shoot growth but positively correlated (r = +0.98) to root growth.
Allelopathic effects of lantana (Lantana camaraL. ♯3LANCA) residues (root, shoot), foliar leachates, and the soil (where lantana was grown) on milkweedvine (Morrenia odorataLindl. ♯3MONOD) seed germination and growth over a 30-day period were examined. Foliar leachates or the soil collected from the field where lantana had been growing had no effect on the final germination percentage or the seedling growth of milkweedvine. Incorporation of dried lantana shoot or root material into soil had no effect on the final percentage germination but caused significant reductions in milkweedvine growth over a 30-day test period. Roots were more inhibitory than shoots. Fifty percent of milkweedvine seedlings died within 15 days after germination at 1% (w/w) dried lantana root incorporation into the soil, and higher concentrations increased seedling death. Lantana roots incorporated into the soil produced foliar symptoms such as wilting and desiccation, whereas lantana shoots incorporated into the soil produced yellowing of the foliage of milkweedvine. Allelopathic activity of lantana residues was still strong even after decomposition of lantana residues for 4 weeks prior to the planting of milkweedvine seeds.
Phytotoxic compounds obtained from methanol extracts of field-grown lantana (Lantana camara L.) were quantified in terms of their inhibition of ryegrass (Lolium multiflorum Lam.) seed germination and/or seedling growth. Subsequent partition of the aqueous fraction (derived from drying the MeOH extract in vacuo and redissolving in distilled water) at various pHs with solvents of differing polarity indicated the phytotoxic compounds were both polar and slightly acidic. Thin-layer Chromatographic separation of the acidic butanol fraction in a solvent mixture of butanol, acetic acid, water (4∶1∶5, by volume) yielded an active fraction with anR f value of 0.89-1.0 that was inhibitory to both root and shoot growth of ryegrass. Two other fractions withR f values of 0.04-0.23 and 0.41-0.57 were inhibitory only to root but not shoot growth.
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