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Cucurbit Genetics Cooperative Report 9:104-106 (article 34) 1986

Genetic Analysis of Isozyme Variants in Cucurbita pepo

Weeden, N.F., R.W. Robinson and J.W. Shail

Dept. of Horticultural Sciences, New York Agricultural Experiment Station, Geneva, NU 14456

Considerable isozyme polymorphism has been identified in cultivars of Cucurbita pepo (1,2,3,4), and a correlation between the particular activity bands and fruit types was noted by Ignart and Weeden (1). We report here a genetic analysis of several enzyme systems previously found to be polymorphic. Two linkage groups were identified. Genetic linkage proved not to be the basis of at least one of the isozyme/morphological correlations reported by Ignart and Weeden.

Three crosses were made between C. pepo cultivars: Senator x Table Queen, Goldrush x Table King, and Blackjack x Early Prolific. Senator, Goldrush, and Blackjack were zucchini types displaying the isozyme phenotypes already described (1). The phenotypes for the acorn squash Table King and Table Queen, have also been described (1). The isozyme phenotypes of Early Prolific, a yellow straightneck type, were similar to those reported in (1) for cultivars of this type, except that PGM had the "A" phenotype. Isozyme analysis was performed as described previously (1,3). Additive expression of the parental banding patterns was performed as described previously in the F1 hybrids. Novel bands, representing new heterodymeric forms, also could be seen in the F1 isozyme phenotypes for GPI, AAT, and MDH enzyme systems. Identification of allelic forms was straightforward in systems such as SKDH, LAP, EST, and ALDO, in which one major band was seen in each parent. Genetic analysis of the other enzyme systems was relatively easy once the parental and F1 phenotypes were compared.

The loci identified and their segregation patterns for the appropriate F2 populations are presented in Table 1. In addition to the reported isozyme loci, the Senator x Table Queen F2 segregated for fruit shape (oblong vs. round) and habit (bush vs. vine), the Goldrush x Table King F2 for fruit shape (oblong vs. round) and fruit color (yellow vs. green), and the Blackjack x Early Prolific F2 for fruit color (yellow, light green and dark green) and leaf mottling (M). The data on the morphological characters in this last cross was of poor quality due to a severe infection of powdery mildew in the F2 population. Thus, this data is not presented.

In cross 1236 and 1237 (derived from different Goldrush x Table King F1 plants) nine isozyme loci segregated. In both populations the locus coding the "cytosolic GPI-2" isozymes (1), designated Gpi-c2, was linked to Aat-p2, the locus specifying the more slowly migrating chloroplast AAT isozymes (AAT-5 in Ignart and Weeden) (Table 2). The loci Skdh, Aldo-p, and Est also exhibited non-random assortment (Table 2). In both populations the apparent gene order was Skdh - Aldo-P - Est.

In the Senator x Table Queen F2 population six isozyme loci segregated (Table 1), and one linkage group was identified: Gpio2 - Aat-p2 (Table 2) There also was a correlation between Skdh and growth habit; however, the highly skewed ratio obtained for the habit character (Table 1) suggested that other factors besides genetic linkage may have contributed to this correlation. Eight isozyme loci segregated in the Blackjack x Early Prolific F2 , all displaying phenotypic ratios close to the expected 1 : 2 : 1(Table 1). The loci Skdh and Aldo-p again showed linkage (Table 2). The results also indicated a linkage between the fruit color and the MDH-2 phenotype (data not presented); however, the powdery mildew infestation interfered with the scoring of fruit color, and this linkage requires further verification.

Table 1. Number of individuals with designated phenotypes in F2 populations.

 
Isozyme or Trait
 
Phenotype
 
Cross
N
Fast or +
Heterozygous
Slow or -
x2
Senator x Table Queen
AAT-4
26
6
13
7
0.07
AAT-5
35
9
17
9
0.03
GPI-2
35
10
19
6
1.2
LAP
16
3
7
6
1.4
MDH
35
14
14
7
4.2
SKDH
34
7
22
5
3.8
Fruit Shape
27
18
9
1.0
**
Habit
35
13
 
22
27
Goldrush x Table King
1236
AAT-4
45
11
27
7
2.5
  AAT-5
43
10
24
9
0.6
ALSO
44
16
20
8
3.3
EST
41
15
17
9
2.9
GPI-2
45
12
26
7
2.2
LAP
45
7
30
8
5.0
MDH-3
44
14
22
8
1.6
PGM-2
45
10
28
7
3.1
SKDH
45
16
22
7
3.6
Fruit Shape
38
26
12
0.9
Fruit Color
39
34
5
3.1
 
*
1237
AAT-4
47
11
17
19
6.3
  AAT-5
47
8
22
17
3.6
ALSO
46
8
26
12
1.5
EST
45
10
27
9
1.1
GPI-2
47
8
24
12
1.7
LAP
46
12
19
10
0.26
MDH-3
47
13
28
15
1.9
PGM-2
46
6
24
12
3.7
SKDH
47
6
17
5.2
Fruit Shape
42
33
9
0.28
Blackjack x Early Prolific
AAT-2
53
12
27
14
0.17
AAT-4
54
9
34
11
3.8
ALDO
54
15
26
13
0.22
GFI-2
54
19
27
8
4.5
LAP
46
16
23
7
3.5
MDH-3
54
8
32
14
3.2
MDH-4
54
18
22
14
2.4
SKDH
54
15
25
14
0.33
*Significant at p>0.05
**Significant at p > 0.01

Table 2. Joint segregation data for isozyme loci displaying disgnificant deviation from random assortment.

Loci
No. plants with designated phenotypez
Recomb. Fract.
H
F/F
F/H
F/S
H/F
H/H
H/S
S/F
S/H
S/S
X2
Goldrush x Table King 1326

Gpi-o2 : Aat-p2

43
9
1
0
3
19
2
0
4
5
35.8
13 + 4
Skdh : Aldo-p
44
11
5
0
4
15
1
1
1
6
35.0
16 + 4
Skdh : Est
41
10
4
1
5
12
2
0
1
6
26.7
19 + 5
Aldo-p : Est
40
13
2
0
2
14
1
0
0
8
56.0
6 + 3
Goldrush x Table King 1327
Gpi-o2 : Aat-p2
47
6
2
0
2
20
0
0
5
12
48.8
10 + 3
Skdh : Aldo-p
46
2
6
0
3
16
7
1
1
10
17.6
24 + 5
Skdh : Est
45
3
6
1
2
17
7
1
1
7
13.8
27 + 6
Also-p : Est
44
7
3
0
1
23
1
0
0
9
60.2
6 + 3
Senator x Table Queen
Gpi-o2 : Aat-p2
35
7
2
0
3
14
0
0
3
6
33
12 + 4
Blackjack x Early Prolific
Skdh : Aldo-p
54
9
3
2
4
16
5
0
7
6
22.1
24 + 5
zPhenotypic designations : F = fast; H = heterozygous; S = slow.  

Literature Cited

  1. Ignart, F. and N.F. Weeden. 1984. Allozyme variation in cultivars of cucurbita pepo L. Euphytica 33:779.
  2. Kirkpatrick, K.J., D.S. Decker and H.D. Wilson. 1985. Allozyme differentiation in the Cucurbita pepo complex: C. pepo var. medullosa vs. C. texana. Econ. Bot. 39:289.
  3. Puchalski, J.T. and R.W. Robinson. 1978. Comparative electrophoretic analysis of isozymes in Cucurbita species. Cucurb. Genet. Coop. 1:39.
  4. Wall, J.R. 1969. A partial survey of the genus Cucurbita for electrophoretic variants of esterase and leucine amino peptidase. Southwestern Naturalist 14:141.
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Page citation: Wehner, T.C., Cucurbit Genetics Cooperative;
Created by T.C. Wehner and T. Ng, 1 June 2005; design by C.T. Glenn;
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