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Background
Dalea purpurea (purple prairie clover) is a slender
erect plant that typically grows to 50 cm in height. Flowers are each about 0.53
cm long, in dense cylindrical spikes at the apex of the stem. Flowers are bright
purple-magenta with one large and four smaller petals.
Dalea candida (white prairie clover) is a close relative of
D, purpurea, however the
flowers are white rather than purple (USDA 2003). Both of these native
herbaceous perennials have a potential to be used for landscaping. However, more
information is needed regarding the production of these native plants.
Seeds that are produced by the same plant may vary in size, shape
and color. Such variations may indicate the germination responses of the seed
(Baskin and Baskin 1998). In many species, a number of environmental factors may
occur during seed development that can greatly affect the size, shape, and color
of seeds. Many plants that are grown in low soil moisture and in high
temperature conditions have a low seed yield and seeds that are produced are
smaller in size (Baskin and Baskin 1998).
Often seeds that appear to be healthy fail to germinate when
subjected to conditions that normally support germination. This response may
indicate that the seed has a dormancy preventing the germination of the seed.
Seeds from the same parent plant may have different degrees of dormancy. This
occurrence is referred to as polymorphism. New seedlings will emerge at
different times, reducing competition between plants from the same parent plant.
This temporal separation of seed emergence can be advantageous with regard to
the survival of the species (Bewley and Black 1994).
Objectives
1. Determine the percent of fruits that contain seed for D.
candida and D. purpurea in 2002 and 2003.
2. Examine the variation in germination of plump and dried seeds for
both years.
3. Examine the effect scarification has on the germination of plump
D. candida seeds collected in 2003.
Methods
Fruits of Dalea purpurea were collected 6 September 2002
and 4 September 2003 at Manito Prairie Nature preserve, 6 miles southwest of
Pekin, IL. The Dalea candida fruits were collected 30 August 2002 and 11
September 2003 at Sweetfern Nature Preserve at the east edge of Hopkins Park,
IL.
The number of fruits that contained a seed was determined by
rubbing the fruit between my fingertips until the seed was exposed (25 fruits
per rep, 8 reps). Seeds were divided into two groups, plump and dried, based on
visual characteristics.
Plump and dried seeds (not scarified) from each year for each
species were used for the germination study (25 seeds per rep, 3 reps). Plump
D. candida seeds collected in 2003 were scarified using concentrated H2SO4
for 30 minutes followed by a distilled water rinse. Germination was determined
by placing seeds into Petri dishes on moist filter paper, and then into a
germination chamber at 25ºC and 12 hour photoperiod. Seeds were considered to
germinate when the radicle emerged. Seed that did not germinate and were not
covered with fungi were tested for viability using a 1% solution of
2,3,5-triphenyl-tetrazolium chloride (TTC). Seeds were considered viable if more
than 50% of their surface turned pink. Data were analyzed using an ANOVA
followed by mean separation tests (Duncan’s multiple range test) at 5% level
where applicable. Means and standard errors also were calculated.
Results
The percentage of D. candida and D. purpurea fruits collected in 2002 that contained seed was
significantly higher than the percentage of fruits collected in 2003
that contained seed (Table 1). No significant difference was
found between the plump D. candida seeds collected in 2002 and 2003 in
regards to percent germination. However, the dried seeds collected in 2003
showed a significantly higher percent germination than the dried seeds collected
in 2002 (Figure 1). The percent germination of plump D. purpurea
seeds collected in 2002 did not differ significantly from those collected in
2003. The dried D. purpurea seeds collected in 2002 also did not differ
significantly from those collected in 2003 (Figure 2).
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