Effects of Plant Density on Developmental Phenotypes in Maize
1
Stein
Michael J.
1Department
and Jode W.
2
Edwards
of Agronomy, Iowa State University, Ames, IA and 2USDA ARS, Ames, IA.
Abstract
15.00
8.80
Introduction
Since the 1930’s, the average grain yield in the United States has
increased from 1.5 to 8.5 Mg/ha at the end of the last century, with
similar large increases being reported in nations around the world
(Brekke et al., 2011).
BSSS
BSCB1
8.60
BSCB1
14.00
BSSS(R)C17
V Stage
V Stage
14.50
BSSS
8.40
BSCB1(R)C17
8.20
8.00
0
2
4
6
8
10
12
0
14
Populations:
•Iowa Stiff Stalk Synthetic (BSSS)-Developed in 1934 from the
intermating of 16 inbred lines.
•Iowa Corn Borer Synthetic #1 (BSCB1)-Developed in 1949 from the
intermating of 12 inbred lines.
•BSSS(R)C17 & BSCB1(R)C17- The seventeenth cycle of reciprocal
recurrent selection between the two populations
Procedure:
•The four populations were planted at four different densities, 3.8, 6.7,
9.6, and 12.4 plants/m2.
•The populations were planted in a split-plot arranged in a randomized
complete block with two replications, with the populations as the
whole plot and densities as subplots.
Phenotypes
•On four dates in the growing season, 45, 51, 53, and 58 days after
planting, the growing primary ear shoots were removed from BSSS
plants, measured, and observed for abnormalities.
•On two dates in the growing season, 38 and 49 days after planting, the
leaf stages of the plants were measured for each density in each
population by counting the number of leaf collars.
•Mature ears from the BSSS and BSSS(R)C17 populations were
harvested and their final grain yield characteristics were examined.
2
4
6
8
10
12
14
Plants m-2
Plants m
Figure 1: V Stages Versus Plant Density at 38 Days After Planting
Density by population interaction was significant at p<0.05.
Figure 2: V Stage Versus Plant Density at 49 Days After Planting
Density by population interaction was significant at p<0.0001.
70
60
Results
50
3.8 Plants m
-2
40
V Stage
30
20
12.4 Plants m
-2
0
40
45
50
55
60
Days after Planting
Figure 3: Ear shoot length versus Days after planting for BSSS
Density by days after planting interaction was significant at p < 0.007.
•Vegetative growth stage at 38 and 49 days after planting decreased with increasing plant
density at both collection periods and in in all populations (Fig. 1,2).
•In the BSSS population, the most advanced cycle of selection BSSS(R)C17 had the
largest decrease in V stage with increasing plant density whereas at 49 days after planting
the unselected population, BSSS, had the largest decrease in V stage (Fig. 1,2).
•In the BSCB1 population, there the most advanced cycle of selection, BSCB1(R)C17,
and the unselected base population, BSCB1, had the same response to increasing plant
density (Fig. 1,2).
Ear Shoot Length
•Ear shoots in BSSS increased in length much fast at low density than at high density (Fig
3).
•Ear shoot increased linearly with increasing V stage at both high and low plant density
during the developmental stage studied here. Ear length increased faster, relative to
vegetative growth stage, at low plant density than at high plant density (Fig. 4).
60.00
Ear Shoot Length (mm)
Methods
13.00
-2
Less information has been gathered concerning the effects that high
density has on developmental phenotypes.
To observe how different levels of plant density affect the
developmental vegetative and female reproductive phenotypes in both
improved and unimproved populations of maize.
BSSS(R)C17
11.50
7.60
Associated with yield increases from the 1930s to the present has been
an increase in adaptation to higher planting densities (Brekke et al.,
2011).
Objective:
BSCB1(R)C17
12.00
10
Increased plant densities have been shown to affect silking-anthesis
intervals and total number of leaves in unimproved populations, and
the final grain yield per plant in improved and unimproved populations
(Duvick, 2005; Sangoi, 2000).
13.50
12.50
7.80
Ear Shoot Length (mm)
The Iowa Stiff Stalk Synthetic population, BSSS, and the Iowa Corn
Borer Synthetic #1 population, BSCB1, have undergone 17 cycles of
reciprocal recurrent selection. Primary emphasis of selection has been
for grain yield and agronomic performance. Recent studies have shown
that selection for grain yield has greatly increased the adaptation of the
population to high plant density. Advanced cycles achieve maximum
grain yield at much higher densities than early cycles. However, less is
known about the impact of high plant density of early plant
development and morphology. The objective of this experiment was to
examine the effect of plant density on morphological and female
inflorescence development in BSSS and BSCB1 populations.
Unselected base populations and the cycle 17 populations and
population crosses were planted at four different densities in two
replicates ranging from 3.8 to 12.4 plants/m2 at the Iowa State
University Agronomy Farm outside Ames, Iowa. High plant density
reduced rate of morphological development and the rate of female ear
development beginning early in development suggesting that
understanding the effects of plant density on agronomic performance
will require characterization of the effects of high plant density on
early plant development.
50.00
3.8 Plants m-2
40.00
Final Ear Length
30.00
•Mature ear length decreased at a rate of 4.1 mm for every 1.0 plant m-2 increase in plant
density (data not shown). However, no differences were found between improved and
unimproved populations in final ear length. Two hypotheses for the lack of difference in
populations in final ear length are small experiment size (statistical power) and wind
damage after pollinating that reduced effective plant density at the higher planting
densities.
12.4 Plants m-2
20.00
10.00
0.00
0
5
10
15
20
25
V Stage
Figure 4: Ear Shoot Length Versus Leaf Stage for BSSS
Density by V stage interaction for slope of the two lines was significant
at p<0.04.
Discussion
We found that high plant density delayed vegetative development and female reproductive
development. Selection reduced the developmental delay in BSSS (BSSS had a much
greater delay than the advanced population, BSSS(R)C17) but not in BSCB1. In the BSSS
population, high plant density reduced the rate of growth of the developing ear shoot
relative to time, showing a delay in female reproductive development. High plant density
also slowed the growth of the ear shoot relative to the development of the leaf stage
suggesting that plant density also affects relative rates of vegetative and female
reproductive development
Future work is planned to study more vegetative and reproductive phenotypes to better
characterize the differential impact of plant density in improved and unimproved
populations.
Acknowledgements
We would like to thank the Paul Scott and Erik Vollbrecht Labs for allowing us
to use their lab space and microscopes to dissect the ear shoots.
References
Brekke, B., Edwards, J., and Knapp, A. 2011. Selection and adaptation to high
plant density in the Iowa stiff stalk synthetic maize (Zea mays L.) population: II.
plant morphology. Crop Sci. 51:2344-2351.
Duvick, D. 2005. The contribution of breeding to yield advances in maize (Zea
mays L.). Advances in Agronomy 86:83-145.
Sangoi, L. 2000. Understanding plant density effects on maize growth and
development: An important issue to maximize grain yield. Ciência Rural
31:159-168.