Transcript Slide 1

DROUGHT AVOIDANCE CHARACTERISTICS OF HYBRID BLUEGRASS
AND TALL FESCUE CULTIVARS
Leonard Githinji, Jacob Dane, Robert Walker, and Edzard van Santen
Auburn University, Agronomy and Soils Department, 285 Funchess Hall, Auburn, AL 36849-5412
INTRODUCTION
Tall fescue (Festuca arundinacea Schreb.) has been reported to have superior drought
avoidance and is able to maintain growth and green color for longer periods compared to
many other cool-season species (Sleper and West, 1996).
Kentucky bluegrass (Poa pratensis L, KBG) has good turf quality and forms attractive
turf when supplied with adequate water but has moderate to low drought resistance
(Beard, 1989). The grass usually goes dormant and loses color during periods of high
temperature and drought.
While tall fescue has good drought resistance, it is not as fine textured as KBG.
Furthermore, some turfgrass managers and home owners prefer the finer texture and
recuperative capacity that KBG offers (Bremer et al., 2006).
Hybrid bluegrasses (HBG) are genetic crosses between KBG and Texas bluegrass (Poa
arachnifera Torr., TBG). They have the desirable appearance of KBG and like TBG, may
withstand higher temperatures and extended drought without going dormant.
Although HBGs have potential for lawns and golf courses, there is little scientific
information available about their performance relative to KBG and tall fescue under
different climatic stresses or cultural practices (Bremer et al., 2006).
Table 1. Results from mixed models ANOVA for root mass and root length density (RLD). Fourand three-way interactions were dropped from the model because of P-values ≥ 0.50.
Degrees of freedom
Source of
Variation
P>F
Determining the turf color quality, root length density and root dry mass under different
stress regimes.
Comparing the performance of the hybrid bluegrasses (HB 129, HB 130, HB 328 and
HB 329) with tall fescue cultivars (Green Keeper and KY 31).
Root Length Density (RLD) and Root Dry Mass (RDM)
Numerator
Denominator
Root mass
RLD
Irrigation (I)
2
16
0.144
0.059
Cultivar (C)
5
160
0.382
<0.001
I×C
10
160
0.937
0.170
Year (Y)
1
160
<0.001
<0.001
I×Y
2
160
0.683
0.001
C×Y
5
160
0.373
0.060
Month (M)
1
207
<0.001
<0.001
I×M
2
207
0.120
0.437
C×M
5
207
0.295
0.027
M×Y
1
207
<0.001
0.056
The RLD over the entire 2-year period was significantly (P = 0.001) affected by
cultivar (C), year (Y), and month (M), but not by irrigation (Table 1).
The only important (P ≤ 0.15) two-way interactions involving cultivars were the
C x M and the C x Y interaction.
The results for pair-wise comparison showed that in the 2-yr period the RLD for
HB 130 (average RLD = 8.9 cm cm-3) was significantly (P ≤ 0.001) higher than
that of any other cultivar except HB 129 (Table 2).
In every case the RLD was significantly larger in July than in September (Fig.
1).
The RLD was higher during the close-to-normal year (2005) compared to the
extreme dry and hot year 2006 (Fig. 2).
Table 2. Pair-wise differences for RLD among the hybrid bluegrass and tall fescue cultivars.
Differences are given below the diagonal and P-values above the diagonal.
Objectives
Cultivar
HB 129
HB 129
HB 130
1.19
HB 328
-0.91
The RLD ranking using the combined means for the 2-yr period was
HB 130 (best) > HB 129 > HB 329 > HB 328 > Green Keeper > KY 31.
HB 130
HB 328
HB 329
G. Keeper
KY 31
Avg. RLD
(cmcm-3)
0.083
0.307
0.618
0.001
< 0.001
7.7
< 0.001
0.001
< 0.001
< 0.001
8.9
0.996
0.215
0.093
6.8
2.10
METHODS AND MATERIALS
Location
The location of the experiment was the Auburn University Turfgrass Research Facility,
Auburn, AL.
-0.69
-1.88
0.22
0.071
G. Keeper
-1.91
-3.10
-1.00
1.22
KY 31
-2.08
3.27
1.17
1.39
0.024
7.1
0.999
5.8
0.17
For the entire 2-yr period turf color quality was significantly (P = 0.05) different
for cultivar (C), year (Y), and week (W).
Among the 2-way interactions involving irrigation, only I × C interaction is of
interest in the context of evaluating the color response of cultivar.
The C × Y and C × W interactions were both significant (P  0.001) indicating
that the turf color trait differences among cultivars were dependent on the year
and time of year (Table 3).
5.7
The ranking for turf quality was based on hue, saturation and brightness was
HB 329 (best) > HB 328 > HB 130 > HB 129> KY31 > Green Keeper.
Table 3. Results from mixed models analysis of variance for turf color response variable hue,
saturation, and brightness.
Experimental Set-up
The experimental design was a 6 by 6 Latin square with six replicates of each treatment
combination within an irrigation block
Combined RLD and turf color quality
Source of
Variation
Degrees of freedom
P>F
Numerator
Denominator
Hue
Saturation
Brightness
Irrigation (I)
2
3
0.686
0.129
0.495
Cultivar (C)
5
15
<0.001
<0.001
<0.001
Turf Color Quality Determination
I×C
10
16
0.551
0.872
0.461
Turf images were taken with the aid of a digital camera once a week from June through
September. The average RGB levels of the digital images were calculated using
SigmaScan Pro version 5.0 software (SPSS, 1999). The digital values of RGB were
converted to HSB values.
Year (Y)
1
3
0.009
0.001
0.122
I×Y
2
3
0.126
0.090
0.848
C×Y
5
585
<0.001
<0.001
<0.001
I×C×Y
10
585
<0.001
<0.001
0.019
Week (W)
13
585
<0.001
<0.001
<0.001
Root samples were collected from each plot in July and September.
I×W
26
585
0.008
0.005
0.090
The sampling depth was 0-10 cm below the surface.
C×W
65
585
<0.001
<0.001
0.001
I×C×W
130
585
1.000
1.000
0.829
W×Y
12
585
<0.001
<0.001
<0.001
I×W×Y
24
585
<0.001
0.007
0.221
C×W×Y
60
585
<0.001
<0.001
<0.001
Three ET-based irrigation replacements were applied to meet 100%, 80% and 60% of
potential evapotranspiration and irrigation was treated as an external variable.
Determination of Root-Length Density and Mass
The roots were stained with Congo red dye.
Root-length measurement was done using a Comair root length scanner, calibrated to
known lengths and widths of thread.
Root-length density (RLD) was eventually calculated by dividing total root length in
centimeters by the volume of the sampler in cubic centimeters.
July
September
2005
14
Mixed models as implemented in PROC MIXED of PC SAS Version 9.1.3 (SAS Institute,
2006) was used to analyze the response data.
-3
10
a
a
8
6
a
a
b
b
b
a
b
b
b
4
2
For RLD and RDM this involved analysis as a replicated Latin square (cultivars=6,
rows=6, columns=6), where irrigation was treated as an environmental factor with three
levels.
HB 329 (best) > HB 130 > HB 328 > HB 129 > KY 31 > Green Keeper.
CONCLUSIONS
The results of this study showed that hybrid bluegrasses performed better in
terms of root length density and turf color quality, and would likely withstand
drought better than tall fescue cultivars.
Furthermore, the authors suggest that hybrid bluegrass cultivars were able to
withstand summer heat better than tall fescue cultivars.
This is collaborated by visual observations and digital pictures which showed
considerable browning for the tall fescue plots, but not for hybrid bluegrasses.
2006
REFERENCES
12
-3
a
Root Length Density (cm.cm) .
Statistical Analysis
The ranking based on RLD and turf color quality was:
14
12
Root Length Density (cm.cm)
Root dry mass (RDM) was recorded after oven drying for 72 h at 80° C.
Drought resistance has been correlated with root length, extensive root system
or root length density in field crops and turfgrass.
Turf Color Quality

HB 329
RESULTS AND DISCUSSIONS
10
8
Beard, J.B. 1989. Turfgrass water stress: Drought resistance components, physiological
mechanisms, and species-genotype diversity. p. 23–28. In Takatoh H. (ed.) Proc.
Japanese Soc. Turfgrass Sci., Tokyo, Japan
a
a
b
a
b
a
a a
6
a
a
b
b
Bremer, D. J., K. Su, S. J. Keeley, and J. D. Fry. 2006. Performance in the transition
zone of two hybrid bluegrasses compared with Kentucky bluegrass and tall fescue.
Applied Turfgrass Science.10:1094.
4
2
0
0
HB 129
HB 130
HB 328
HB 329
Green Keeper Kentucky 31
Fig. 1. Cultivar x month interaction means for
root length density.
HB 129
HB 130
HB 328
HB 329
Green Keeper Kentucky 31
Fig. 2. Cultivar x year interaction means for
root length density.
Sleper, D.A., and C.P. West. 1996. Tall fescue. p. 471–502. In Moser L.E. (ed.) Coolseason forage grasses. Agron. Mon. 34. ASA, CSSA and SSSA, Madison, WI.