Evaluating the mass based
germination response of Rudbeckia
mollis seeds to heat stress
Nicholas Genna
Environmental Horticulture Department
University of Florida
Problem Statement
Objective
• Determine if heat stress promotes unique
germination responses in mass-separated
Rudbeckia mollis seeds.
Rudbeckia mollis (Asteraceae)
http://hawthornhillwildflowers.blogspot.com/2009/06/softhair-coneflower.html
http://www.florida.plantatlas.usf.edu/photo.aspx?ID=2980
Tia Tyler
Methods
Germination Tests
• Alternating temperatures
–
–
–
–
22/11oC (winter)
27/15oC (spring)
29/19oC (fall)
33/24oC (summer)
• Constant temperatures
–
–
–
–
–
27.5oC
30.0oC
32.5oC
35.0oC
37.5oC
Mass Based Germination
Response to Extended
Thermoinhibition Stress
• Exposed seeds to 37oC for 1-10 days
• Transferred seeds each day to 25oC
Test
P-value
Log-rank
<0.0001
Germination is Dependent on
Alternating Temperature and
Not Mass
Covariate
P-value
Hazard Ratio
Mass Class
0.4250
0.956
Temperature
<0.0001
0.914
Rudbeckia Mollis Germinates
Uniquely by Season
Comparison
P-value
22/11 vs 27/17
0.0002
22/11 vs 29/19
<0.0001
22/11 vs 32/24
0.0012
27/17 vs 29/19
0.0034
27/17 vs 32/24
<0.0001
29/19 vs 32/24
<0.0001
Test
P-value
Log-rank
<0.0001
Germination is Dependent on
Constant Temperature and Not
Mass
Covariate
P-value
Hazard Ratio
Mass Class
0.3746
1.053
Temperature
<0.0001
0.699
Rudbeckia Mollis Germination
Probability Decreases with
Increasing Temperature
Comparison
27.5 vs 30.0
27.5 vs 32.5
27.5 vs 35.0
30.0 vs 32.5
30.0 vs 35.0
32.5 vs 35.0
P-value
0.1685
<0.0001
<0.0001
<0.0001
<0.0001
<0.0001
The Probability of Germination
Decreases with Extended
Thermoinhibition Stress
Covariate
P-value
Hazard Ratio
Mass Class
0.1490
1.044
Days
Thermoinhibited
0.0225
0.983
Germination response
• Germination is high (≥ 86%) under cool to
warm temperatures (winter, fall, spring, 27.532.5oC) and similar among mass classes.
• Germination is reduced and temporal patterns
of germination diverge under high alternating
(summer) and high constant temperatures
(35.0oC).
Thermoinhibition
• Mass classes behave similarly in their
response to the release of thermoinhibition.
• The probability of germination decreased with
increasing duration of thermoinhibition.
Conclusions
• Seed mass does not influence germination in
response to heat stress.
• Variation in seed mass should not affect
propagation or restoration efforts with
Rudbeckia mollis.
• Extended exposure to temperatures ≥ 37.0oC
will reduce the probability of germination over
time.
The preceding presentation was delivered at the
2015 National Native Seed Conference
Santa Fe, New Mexico April 13-16, 2015
This and additional presentations available at
http://nativeseed.info