LI, XIAOJIE* AND STEVEN A. FENNIMORE. Department of Vegetable Crops, University of California, Davis, c/o USDA ARS, 1636 East Alisal Street, Salinas, CA 93905. - Temporal changes in germinability and light response of seeds of six common weed species.
Freshly-matured seeds of Amaranthus retroflexus, Capsella
bursa-pastoris, Lamium amplexicaule, Spergula
arvensis, and Urtica urens (collected on 29 Oct.-3 Nov.,
1999) and of Portulaca oleracea (collected on 21 Sep., 1999)
were (1) incubated for 3 mo at approximated prevailing soil (5 cm
below surface) temperatures of arable lands in Salinas, CA, with long
(10 hr daily) or short (< 2 min weekly) exposure to light (Experiment
1); or, (2) subjected to natural temperature conditions by burial at a
depth of 5 cm in the field or dry-storage in paper bags in a
non-heated warehouse room (Experiment 2). For Experiment 2, after 1.5
and 3 mo, seeds were incubated for 14 d in the same manner as
described above to detect temporal changes in germinability and light
response. Results showed that short light exposure did not satisfy
the germination requirement of freshly dispersed seeds of any species
except A. retroflexus. Following burial, seeds of U.
urens and A. retroflexus germinated to significantly lower
percentages after long exposure compared to short exposure, whereas
those of C. bursa-pastoris, L. amplexicaule, and S.
arvensis responded indifferently to the light exposure conditions
and those of P. oleracea retained their absolute dependence on
long exposure for germination. At approximated prevailing soil
temperatures, newly-matured seeds of all species, except P.
oleracea (with a percent germination of 76 ± 2), exhibited low
germinability (ca. 0-11%), which increased significantly after burial
in soil. Compared to burial, dry-storage essentially resulted in
similar germination responses to the light conditions but with
significantly lower percent germination for all species.
Key words: dry-storage, Portulaca oleracea and five other common weed species, seed burial, temporal changes in germinability and light response