MOLECULAR MAPPING OF LEAF CUTICULAR WAXES IN WHEAT
S. MONDAL, R.E. MASON, F. BEECHER AND D.B.HAYS
TEXAS A& M UNIVERSITY, DEPT. OF SOIL & CROP SCIENCES, COLLEGE STATION, TX-77845
ABSTRACT
Leaf cuticular waxes in plants provide protective barrier to biotic and abiotic stresses. The objective of this study was to identify quantitative trait loci (QTL) associated with leaf waxes in wheat. A
RIL population was derived from a cross of Halberd and Karl 92 was grown in the greenhouse. Plants were grown in the greenhouse at 25C/ 20C day/night temperatures respectively. Leaf wax was
collected at 10 DAP from the flag leaf. Flag leaf temperature and leaf width was measured in the greenhouse. The RIL population was evaluated for yield and yield components. 190 SSR markers
were polymorphic between the parent lines. Preliminary QTL analysis identifies QTLs associated with leaf wax on chromosome 2A, 5D and 4 A.
INTRODUCTION
RESULTS
Plant cuticular layer is a thin hydrophobic layer that
covers the primary aerial plant surfaces and protects
from biotic and abiotic stresses. The cuticular layer is
composed of cutin and waxes. Cutin forms the
framework of the cuticular matrix with the waxes
embedded ( intracuticular wax) and also deposited on
the surface ( epicuticular wax).
2
Leaf Wax (mg/dm )
HALBERD
KARL92
Leaf cuticular waxes affect stomatal conductance, leaf
temperatures and surface reflectance. In wheat leaf
epicuticular wax increases under drought stress.
Studies by Johnson et al (1983) reported significant
associations of wheat leaf waxes with reduced leaf
temperatures and yield.
2
1
0
2
3
4
o
Temperature Depression C
Figure 1. SEM images of flag leaf surface of the parent lines Karl92 and
Halberd
Leaf Wax (mg/dm )
2
3.00
Year 1
2.50
Year 2
Figure 3. Relationship between flag leaf wax content
(mg/dm2)and temperature depression °C (ambient temperature –
leaf temperature)
2.00
DISCUSSION
1.50
Significant difference in wax content between the
parent lines (α = 0.05)
1.00
0.50
Leaf temperature depression positively correlated to
leaf wax content ( R=0.4695, α = 0.05)
0.00
Karl92
Halberd
3 QTLs identified from the parent Halberd. A QTL on
5D is in the same region in both years.
OBJECTIVE
• Map QTLs associated with flag leaf wax
content in wheat
Figure 2. Flag leaf wax content of the parent lines Karl92 and Halberd in
Year1 2008 and Year2 2009
1 QTL on 1B from the parent Karl92 is present in
both years of greenhouse study
• Define the interaction between QTLs for leaf
wax content and phenotypic and physiological
traits
Table 1. Preliminary mapping result of flag leaf wax content in year 2008 and year 2009
A 120 Recombinant Inbred Lines (RIL) population
was developed from a cross of Halberd and Karl 92
wheat lines. The population was grown in the
greenhouse at 25°C/20°C day and night temperature
respectively
3
1
Various genes controlling wax production and
movement have been identified in Arabidopsis,
maize, barley and rice. In wheat no genes or
molecular markers associated with leaf cuticular
waxes have been reported. This study aims at
identification of regions in wheat chromosomes that
may be associated with flag leaf wax content.
MATERIALS & METHODS
R2 = 0.2204
4
YEAR 2008
Chromosome Marker Name
Marker
Position
LOD Score
Additive
R2
FURTHER WORK
RIL population will be grown in the field in
multiple locations to check the validity of the
QTLs observed
Analysis of the phenotypic data and physiological
data to define the interaction with leaf wax
content
1B
wmc156
31
4.7
-0.0610
0.1191
5D
gwm292
71.7
2.53
0.0496
0.0884
• Leaf wax was extracted and quantified by
colorimetric technique (Ebercon 1977) at 10DAP
6A
wmc417
80.8
2.9
-0.0518
0.0926
REFERENCES
•Leaf waxes were visualized by SEM imaging
(TAMU-MIC) using Au-Pd sputter coating method.
YEAR 2009
1B
wmc156
31
4.1
-0.0188
0.1287
•Leaf temperature was recorded with a infra-red
thermometer and porometer respectively
2A
gwm545
17
6.5
0.0242
0.1890
Ebercon, A.., Blum A. and Jordan W.R. 1977. A
rapid colorimetric method for epicuticular wax
content of sorghum leaves. Crop Science. 17:
179-180
• Phenotypic data such as kernel number, kernel
weight etc was collected
• A genetic linkage map has been developed for the
RIL population ( Mason et al 2009. in prep). Single
marker analysis and composite interval mapping
were performed in QTL Cartographer
4A
wmc497.1
123.3
2.6
0.0123
0.0521
5D
cfd26
31.2
3.5
0.0139
0.0660
7B
barc267
43.2
7.6
-0.0239
0.1860
Johnson, D.A., R.A. Richards, and N.C.
Turner.1983. Yield, water relations, gasexchange, and surface reflectances of nearisogenic wheat lines differing in glaucousness.
Crop Sci. 23: 318–325
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