Mapping of QTL for Fruit Size and Shape Traits 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
Zhoo-Hyeon Kim
Department of Horticulture, Gyeongsang National University, Chinju, 660-701, South Korea
Introduction: Mature fruit size and shape
are important traits of most melon (Cucumis
melo L.) types. The former is also an
important component of yield in melon.
Information on molecular markers linked to
genes for these fruit traits may contribute to
our understanding of the genetics of fruit size
and shape and offer prospects for the use of
molecular markers in modification or
maintenance of fruit characteristics in melon
breeding programs. Therefore, our objective
was to identify RAPD markers linked to QTL
for fruit weight, length, and diameter in an
existing molecular marker-based linkage map
constructed by means of an F2 population
derived from the melon cross of >Deltex=
(larger fruit size) x TGR1551 (smaller fruit
size).
Materials and Methods: One hundred-eight
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 larger fruit size, while
the TGR1551 parent is a wild type with
smaller fruit size. Phenotypic data for fruit
weight, length, and diameter were recorded
from the 108 F2 plants along with their
parents. 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 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 fruit weight,
length, and diameter. 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 fruit size and shape traits 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 fruit weight,
length, and diameter were observed in the F2
population (Figure 1), indicating that the fruit
size and shape traits were quantitatively
inherited. Mature fruit weight was found to be
significantly and positively correlated with
fruit length and diameter in the population
(Table 1). We also noted a significant positive
correlation between fruit length and diameter.
Twenty-two 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 controlling fruit weight, length, or
diameter in the F2 population of the >Deltex= x
TGR1551 cross in the greenhouse on the basis
of SLR (Table 2).
A total of nine RAPD markers were identified
to be significantly associated with QTL for
fruit weight in our population based on SLR
Cucurbit Genetics Cooperative Report 28-29: 31-34 (2005-2006)
31
(Table 2, Figure 2). Seven unlinked markers
associated with QTL were significant in a
SMR analysis where the full model explained
42% of the total phenotypic variation for fruit
weight.
These RAPD markers associated with QTL
controlling the mature fruit size and shape
traits in the molecular linkage map identified
here are expected to be useful in melon
breeding programs for modifying fruit size.
Five markers were detected to be significantly
associated with QTL regulating fruit length in
this population by means of SLR (Table 2,
Figure 2). Particularly, marker OR02.850 on
linkage group 7 amplified from >Deltex=
accounted for 20% of the phenotypic
variation for the trait. The five markers were
significant in the SMR analysis with a total
phenotypic variation of 40% for the fruit
length trait.
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.
We found significant associations of eight
RAPD markers, located on several different
linkage groups of the molecular linkage map,
with QTL affecting fruit diameter in the
population on the basis of SLR (Table 2,
Figure 2). Seven markers were significant in
the SMR analysis with a total phenotypic
variation of 37% for the fruit diameter trait.
Of the RAPD markers associated with nine
QTL for fruit weight in the molecular markerbased linkage group detected here, four on
linkage groups 3, 6, 7 and 9 and three on
linkage groups 3, 7 and UP3 (Figure 2) were
also observed to be significantly associated
with QTL for fruit length and diameter,
respectively (Table 2), suggesting that in this
cross these fruit size and shape traits are
controlled partially by the same QTL.
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. Pearson correlations of fruit weight, length, and diameter in an F2 population derived
from the melon cross of >Deltex= x TGR1551.
Fruit weight and length
0.79**
**Significant at P < 0.01.
32
Fruit weight and diameter
Fruit length and diameter
0.73**
0.24**
Cucurbit Genetics Cooperative Report 28-29: 31-34 (2005-2006)
Table 2. Simple linear regression (SLR) and stepwise multiple regression (SMR) analyses of
marker and data for detection of QTL for fruit weight, length, and diameter in an F2 population
derived from the cross of >Deltex= (larger fruit weight) x TGR1551 (smaller fruit weight).
Fruit
trait
Weight
RAPD
marker
OB06.900
OI03.600
OP17.900
OJ04.450
OQ15.1000
OG05.1050
OG09.300
OK04.600
OA10.1250
Linkage
group
7
7
9
6
3
unassigned
10
unassigned
2
SLR
SMR
2
P
0.000
0.001
0.003
0.005
0.008
0.026
0.038
0.028
0.047
Length
OR02.850
OP17.900
OJ04.450
OQ15.1000
OJ13.400
7
9
6
3
unassigned
0.000
0.001
0.017
0.030
0.040
20
9
5
4
4
Diameter
OI03.600
OI11.1900
OM06.500
OJ07.900
OC15.1400
OK20.700
OL18.500
OB16.500
7
unassigned
6
3
2
11
12
unassigned
0.002
0.004
0.016
0.011
0.013
0.028
0.034
0.049
8
8
5
6
6
4
4
4
14
Number of F2 plants
12
10
8
6
20
15
R2
10
9
7
6
4
3
3
Cumulative R2
0.000
0.001
0.015
0.032
0.043
Cumulative R2
0.002
0.004
0.011
0.013
0.015
0.033
0.047
42
20
9
5
3
3
40
8
8
5
5
5
3
3
Cumulative R2
37
35
25
Fruit weight
Deltex=923
TGR1551=421
Mean=1015
Std Dev=338
P
0.000
0.001
0.004
0.007
0.026
0.034
0.045
R
10
9
8
7
6
5
4
4
4
Fruit length
Deltex=142
TGR1551=108
Mean=154
Std Dev=33
Fruit diameter
Deltex=115
TGR1551=87
Mean=112
Std Dev=11
30
25
20
15
10
4
10
5
5
2
0
0
300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800
Fruit weight (g)
0
70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220
Fruit length (mm)
70
80
90
100
110
120
130
140
Fruit diameter (mm)
Figure 1. Frequency distributions for fruit weight, length, and diameter of F2 plants derived from
the melon cross of >Deltex= (larger fruit weight) x TGR1551 (smaller fruit weight).
Cucurbit Genetics Cooperative Report 28-29: 31-34 (2005-2006)
33
0
1
OJ04.1000
0
2
0
OM11.750
3
OC14.1400
0
4
0
OK10.1500
5
OM18.600
0
6
OF15.300
OF16.300
0
7
OB06.900
OK10.550
OG18.500
OJ09.350
OH03.500
FW
OJ20.500
OR15.800
OH19.1300
OA07.800
OA10.1250
OA01.450
OJ16.300
OM01.500
OM09.500
OG06.750
FD
OA09.300
OG17.800
OC19.450
OM20.700
OH16.600
OD08.750
OD08.400
OA09.850
OK01.400
OA02.1500
FD
OC15.1400
OJ15.1300
FD
OQ15.1000
OB16.1150
OB16.1000
OC15.850
106
OG17.600
FL 0 9
OL07.1100
FW
8
0
FW
OI12.300
10
OM09.2200
82
40
39
0
UP1
OB06.1250
OF05.500
OH07.600
OO05.2100
OJ04.450
OE14.700
OI03.600
OK20.700
0
12
OC02.600
OK12.700
OE01.1350
OG12.400
OF12.400
OL18.500
OI06.500
0
4
36
UP2
OE09.450
OF03.1600
OM14.500
OAA09.650
OC11.450
OD13.600
OM06.700
OA05.450
OC20.700
OC11.700
OK14.1350
OAU05.350
OE01.250
OB04.900
OG17.250
OI10.550
OF04.600
OH07.700
OJ11.850
OG09.650
67
27
11
OK16.800
OM11.500
OI12.500
OI19.300
OK15.1000
OI19.650
OH11.250
OAT03.250
OM13.300
OM01.950
OE04.300
OA15.850
FL
OK06.650
OK06.550
93
0
FD
OM07.400
FW
FD
OK13.600
OB12.550
OA16.450
OJ14.300
OC16.200
OJ19.400
OK01.1250
OM11.2000
OK16.900
OA12.600
OG09.300
OD07.2100
OB12.2000
OC07.350
OC02.550
OR06.650
ON08.350
OA15.400
OP17.900
OC09.1600
OK20.1050
OL20.850
FW
OC09.600
OJ07.900
91
FD
OA05.1600
FL
OAU05.700
0
OQ15.1500
FL
OH07.300
OJ15.550
FW
OF10.600
130
OB17.1050
OM18.300
ON08.600
OA18.650
OA16.1000
OK20.800
OR04.900
OC09.800
OL04.1500
OK01.600
OK03.450
OM11.1250
OG16.650
OE08.600
OK17.600
OR02.850
FW
OH16.500
OI20.650
OG17.1050
OI06.800
OL12.2100
OJ04.550
OA19.900
OM06.500
OR02.400
OAS14.350
OL15.300
OJ19.450
OAP03.600
178
80
OH06.1600
OC02.1250
153
OE17.400
FD 0 UP3 OI11.1900
FW
22
OK04.600
OK17.700
Figure 2. Linkage map for the >Deltex= x TGR1551 mapping population with locations of QTL for
melon fruit size and shape traits. Bars to the left of each linkage group indicate the intervals having
significant trait associations (P < 0.05). For traits evaluated in the present study: FW=fruit weight;
FL=fruit length; and FD=fruit diameter.
34
Cucurbit Genetics Cooperative Report 28-29: 31-34 (2005-2006)