Mapping of QTL for Sugars in Ananas Melon
Soon O. Park and Kevin M. Crosby
Texas Agricultural Research and Extension Center, Texas A&M University, Weslaco, TX 78596
and Vegetable & Fruit Improvement Center, Texas A&M University, College Station, TX 77843
Kil S. Yoo
Vegetable & Fruit Improvement Center, Texas A&M University, College Station, TX 77843
Zhoo-Hyeon Kim
Department of Horticulture, Gyeongsang National University, Chinju, 660-701, South Korea
Introduction: Sugar components such as
sucrose, fructose, glucose, and total soluble
solids are major factors influencing mature
melon (Cucumis melo L.) fruit sweetness.
Molecular markers linked to genes
regulating synthesis of sugar components
may improve the breeder=s ability to recover
high sugar genotypes and aid in the
development of high sugar cultivars.
Therefore, our objective was to identify
RAPD markers associated with QTL for
sucrose, glucose, fructose, total sugars (TS),
and total soluble solids (TSS) in an existing
molecular marker-based linkage map
constructed by means of an F2 population
derived from the melon cross of >Deltex=
(high sugars) x TGR1551 (low sugars).
Materials and Methods: One hundredeight F2 plants from the cross of >Deltex= x
TGR1551 were planted in a greenhouse at
the Texas Agricultural Research and
Extension Center-Weslaco in 2003. The
>Deltex= parent is an ananas type with good
fruit quality, while the TGR1551 parent is a
wild type with poor fruit quality. Data for
sucrose, glucose, fructose, and TS were
obtained from the 108 F2 plants using
HPLC. Total soluble solids data were also
obtained from the F2 plants using a
temperature corrected refractometer with
digital readout. A RAPD marker-based
linkage map was recently developed by Park
and Crosby (3) using the 108 F2 plants of
the same cross. MAPMAKER version 3.0
(2) was used for the linkage analysis of 208
RAPD markers. The name of each RAPD
26
marker is derived from an AO@ prefix for
Operon primers, the letters identifying the
Operon kit, Operon primer number, and the
approximate length (bp) of the marker (3).
Simple linear regression (SLR), for each
pairwise combination of quantitative traits
and marker loci, was used to analyze the
data for detection of QTL affecting sucrose,
glucose, fructose, TS, and TSS content.
Significant differences in trait associations
were based on F-tests (P<0.05) (1). Loci
with the lowest P value per QTL were
chosen and then were added in a stepwise
multiple regression (SMR) to select the best
set of markers (P<0.05) for prediction of the
total trait phenotypic variation explained by
the identified QTL (4). Pearson correlations
of mature fruit sweetness traits including
three sugars were also determined in our
population. All statistical analyses were
conducted using the Statistical Analysis
System (SAS Inst., Cary, N.C.).
Results and Discussion:
Continuous
frequency distributions for sucrose, glucose,
fructose, TS, and TSS were observed in the
F2 population (Figure 1), indicating that the
fruit sweetness traits were quantitatively
inherited.
Twenty-four RAPD markers, located on
several different linkage groups of the
molecular marker-based melon map (Figure
2), were found to be significantly associated
with QTL affecting sucrose, glucose,
fructose, TS or TSS in the F2 population of
Cucurbit Genetics Cooperative Report 28-29: 26-30 (2005-2006)
the >Deltex= x TGR1551 cross in the
greenhouse based on SLR (Table 2).
Two RAPD markers were significantly
associated with QTL for sucrose content in
our population on the basis of SLR (Table
2). The two markers on linkage groups 1 and
3 associated with QTL (Figure 2) were
significant in a SMR analysis where the full
model explained 10% of the total phenotypic
variation for sucrose. Five markers were
significantly associated with QTL regulating
glucose content in this population by means
of SLR. Particularly, three unlinked markers
(OK10.1500, OJ09.800, and OG17.1050),
amplified from >Deltex=, accounted for 10%
to 12% of the variation for the trait. The five
markers were significant in the SMR
analysis with a total variation of 32% for the
glucose trait. We identified significant
associations of nine RAPD markers, located
on different linkage groups, with QTL
controlling fructose concentration in the
population by SLR. Eight markers were
significant in the SMR analysis with a total
fructose variation of 41%. Four unlinked
markers were associated with QTL affecting
TS and TSS in the mapping population
based on SLR, respectively. In the SMR
analysis the two groups of the four markers
were significant with total R2 values of 18%
and 23% for the TS and TSS traits,
respectively.
These RAPD markers associated with the
sugar synthesis QTL in the molecular
linkage map detected here could be useful in
melon breeding for improving the mature
fruit sweetness.
Literature Cited:
1. Edwards, M.D., C.W. Stuber, and J.F.
Wendell. 1987. Molecular markerfacilitated investigations of quantitative
trait loci in maize. I. Numbers, genomic
distribution, and types of gene action.
Genetics 116:113-125.
2. Lander, E.S., P. Green, J. Abrahamson,
A. Barlow, M.J. Daly, S.E. Lincoln, and
L. Newburg. 1987. MAPMAKER: An
interactive computer package for
constructing primary genetic linkage
maps with experimental and natural
populations. Genomics 1:174-181.
3. Park, S.O. and K.M. Crosby. 2007.
Construction of a RAPD marker-based
linkage map in
ananas
melon.
Cucurbit
Genetics
Cooperative
30:submitted.
4. Paterson, A.H., S. Damon, J.D. Hewitt,
D. Zamir, H.D. Rabinowitch, S.E.
Lincoln, E.S. Lander, and S.D. Tanksley.
1991. Mendelian factors underlying
quantitative traits in tomato: Comparison
across
species,
generations,
and
environments. Genetics 127:181-197.
Table 1. Correlations of sucrose, glucose, fructose, total sugars, and total soluble solids in an F2
population derived from the melon cross of >Deltex= x TGR1551.
Sweetness trait
Sucrose
Total soluble solids
0.63**
Total sugars
0.79**
Fructose
-0.30**
Glucose
-0.24*
*,**Significant at P < 0.05 or 0.01, respectively.
Glucose
0.17
0.35**
0.70**
Cucurbit Genetics Cooperative Report 28-29: 26-30 (2005-2006)
Fructose
0.07
0.26**
Total sugars
0.71**
27
Table 2. Simple linear regression (SLR) and stepwise multiple regression (SMR) analyses of marker and
data for detection of QTL for three sugars, total sugars (TS), and total soluble solids (TSS) in an F2
population derived from the cross of >Deltex= (high sugars) x TGR1551 (low sugars).
Sugar
trait
Sucrose
RAPD
marker
OJ07.900
OG16.650
Linkage
group
3
1
SLR
SMR
P
0.009
0.039
R
6
4
Glucose
OK10.1500
OJ09.800
OF05.500
OG17.1050
OK04.600
4
2
unassigned
1
unassigned
0.000
0.000
0.009
0.001
0.022
12
10
6
10
5
Fructose
OE08.600
OR02.800
OK20.1050
OE14.700
OK17.600
OK10.1500
OI12.300
OJ09.800
OJ13.400
1
unassigned
9
7
1
4
3
2
unassigned
0.001
0.005
0.013
0.023
0.007
0.036
0.012
0.019
0.031
10
7
6
5
7
4
6
5
4
2
TS
OE14.700
OC14.1400
OM14.500
OJ09.350
7
3
12
2
0.012
0.030
0.032
0.045
6
4
4
4
TSS
OK10.550
OC18.900
OB12.550
OC14.1400
6
2
8
3
0.002
0.008
0.013
0.021
8
6
6
5
28
P
0.009
0.031
Cumulative R2
0.000
0.003
0.006
0.019
0.033
Cumulative R2
0.001
0.007
0.010
0.013
0.018
0.020
0.023
0.039
R2
6
4
10
12
7
6
4
3
32
10
6
5
5
4
4
4
3
Cumulative R2
0.012
0.021
0.029
0.042
Cumulative R2
0.002
0.009
0.017
0.038
Cumulative R2
41
6
5
4
3
18
8
6
5
4
23
Cucurbit Genetics Cooperative Report 28-29: 26-30 (2005-2006)
Number of F2 plants
25
40
Su crose
D eltex=37.5
TG R 1551=0.0
M ean=16.5
Std D ev=12.2
20
15
G lucose
D eltex=12.6
TG R 1551=14.4
M ean=17.8
Std D ev=4.9
35
30
25
Fructose
D eltex=18.3
TG R 1551=14.3
M ean=15.1
Std D ev=4.5
40
35
30
25
20
20
10
15
15
10
10
5
5
0
5
0
0-5.0
5.1-10.0 10.1-15.0 15.1-20.0 20.1-25.0 25.1-30.0 30.1-35.0 35.1-40.0 40.1-45.0 >45.1
0
5.1-10.0
10.1-15.0
S ucrose (m g/g)
25
Number of F2 plants
45
20
15
15.1-20.0
20.1-25.0
25.1-30.0
30.1-35.0
35.1-40.0
G lucose (m g/g )
5.1-10.0
10.1-15.0
15.1-20.0
20.1-25.0
25.1-30.0
30.1-35.0
Fructose (m g/g)
30
Total sugars
D eltex=68.4
TG R 1551=28.7
M ean=49.2
Std D ev=12.4
TSS
D eltex=10
TG R 1551=3
M ean=7
Std D ev=2
25
20
15
10
10
5
5
0
0
25.1-30.0 30.1-35.0 35.1-40.0 40.1-45.0 45.1-50.0 50.1-55.0 55.1-60.0 60.1-65.0 65.1-70.0 >70.1
Total su gars (m g/g)
3.1-4.0
4.1-5.0
5.1-6.0
6.1-7.0
7.1-8.0
8.1-9.0
9.1-10.0 10.1-11.0
>11.1
TSS (% )
Figure 1. Frequency distributions for sucrose, glucose, fructose, total sugars, and total soluble
solids (TSS) of F2 plants derived from the melon cross of >Deltex= x TGR1551.
Cucurbit Genetics Cooperative Report 28-29: 26-30 (2005-2006)
29
0
1
OJ04.1000
0
2
3
OC14.1400
0
FC
4
0
OK10.1500
5
OM18.600
OG18.500
GC TS
OH03.500
0
OM11.750
OJ09.350
FC
OA10.1250
OA01.450
OJ16.300
OM01.500
OM09.500
OG06.750
TSS
OJ20.500
OA07.800
TS
TSS
OR15.800
OH19.1300
GC
0
OG17.800
OC19.450
OM20.700
FC
GC
OH16.600
OR04.900
OC09.800
OL04.1500
OK01.600
OK03.450
OM11.1250
OG16.650
OE08.600
OA02.1500
OF10.600
OB16.1150
OB16.1000
OD08.750
OD08.400
OA09.850
OK01.400
OC15.1400
106
0
OK17.600
0
8
OJ07.900
40
39
GC
0
10
UP1
OG09.300
0
11
OE14.700
OM11.500
OI03.600
OK20.700
0
12
OC02.600
OK12.700
OE01.1350
OG12.400
OF12.400
OL18.500
OB12.2000
OI06.500
OI12.500
OI19.300
OK15.1000
OI19.650
OH11.250
OB06.1250
OAT03.250
OM13.300
OM01.950
OE04.300
OF05.500
OH07.600
0
4
OA15.850
OO05.2100
OJ04.450
OM07.400
OK06.650
OK06.550
93
TS
OL07.1100
36
UP2
OE09.450
OF03.1600
OM14.500
OAA09.650
OD13.600
178
OH06.1600
OC02.1250
OE17.400
153
0
OG17.250
OI10.550
OF04.600
OH07.700
OJ11.850
80
OC11.450
TS
OM06.700
OA05.450
OC20.700
OC11.700
OK14.1350
OAU05.350
OE01.250
OB04.900
OG09.650
67
27
OK16.800
82
FC
OI12.300
OC07.350
OC02.550
OR06.650
ON08.350
OA15.400
OP17.900
OC09.1600
OK20.1050
FC
OD07.2100
OA05.1600
OG17.600
9
OM09.2200
OB12.550
OA16.450
OJ14.300
OC16.200
OJ19.400
OK01.1250
OM11.2000
OK16.900
OA12.600
OR02.850
OQ15.1500
OC09.600
SC
OK13.600
TSS
OK10.550
OJ15.1300
0
OL20.850
OB06.900
OH07.300
OQ15.1000
OC15.850
130
7
OJ15.550
FC
91
OL12.2100
OB17.1050
OM18.300
ON08.600
OA18.650
OA16.1000
OK20.800
OAU05.700
FC
0
OH16.500
OI20.650
OG17.1050
OI06.800
SC
OF15.300
OF16.300
OJ04.550
OA19.900
OM06.500
OR02.400
OAS14.350
OL15.300
OJ19.450
OAP03.600
OA09.300
TSS
6
GC
22
UP3
OI11.1900
OK04.600
OK17.700
Figure 2. Linkage map for the >Deltex= x TGR1551 mapping population with locations of QTL
for mature melon fruit sweetness traits. Bars to the left of each linkage group indicate the
intervals having significant trait associations (P < 0.05). For traits evaluated in the current study:
SC = sucrose content; GC = glucose content; FC = fructose content; TS = total sugars; and TSS
= total soluble solids.
30
Cucurbit Genetics Cooperative Report 28-29: 26-30 (2005-2006)