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Cucurbit Genetics Cooperative Report 22:16-18 (article 7) 1999

Genetic Control and Linkages of Some Fruit Characters in Melon

C. Perin, C. Dogimont, N. Giovinazzo, D. Besombes, L. Guitton, L. Hagen, and M. Pitrat

INRA, Station de Genetique et d'Amelioration des Fruits et Legumes, BP 94, 84143 Montfavet Cedex (France)

Introduction. Cucumis melo L. is a very polymorphic species, especially for fruit characters like ripening, shape, and flesh color. This variability has been used by botanists to subdivide melon into different major groups. Fruit characters are under genetic control, and the Mendel ian inheritance of some fruit characters like pentamerous locule number and sex expression were demonstrated a long time ago (13). More recently, several fruit-character genes were studied and characterized in the different horticultural groups (12). Improvement of fruit-1uality is an important melon breeding objective. Defining the genetic control of these characters will assist breeders, and their subsequent molecular mapping will contribute to the development of marker-assisted selection (MAS) (14).

In this paper, we describe the genetic control and linkage tests for genes involved in 9 major fruit characters in two different recombinant inbred line (RI) populations.

Methods. Parental lines were 'Vedrantais', an old French inbred line developed by Vilmorin, PI 161375, a Korean line, and PI 414723, an Indian line. The later two are multi-resistant lines used in several breeding programs. the populations studied were 120 F6/F7 RI derived from the cross 'Vedrantais x PI 161375 and 63 F6/F7 RI from the cross 'Vedrantais x PI 414723. the parents, F1 and RI were cultivated under a plastic tunnel in a completely randomized block design with three replications in Avignon (Southern France) during the Summer of 1996 for the PI 414723 population and the Summer of 1997 for the PI 161375 population. four or more fruits of each line were evaluated for fruit characters. The segregation and independence of characters was evaluated using X2 tests.

Results. Nine fruit characters show discrete segregation, eight are under monogenic control and one is under complementary, digenic control (Table 1). The digenic, complementary control of fruit abscission suggests the duplication of an ancestral gene. In a previous study, digenic complementary control of abscission layer formation was found in a cross between 'Pearl' and C68 (15). Genetic control of most of these characters have already been studied but no allelism tests have been done. We have given temporary names to most of the genes found in this study, according to previous work. To our knowledge, empty cavity hasn't been described in Cucumis melo. Carpels of the fruit were separated from each other at ripening leaving a cavity. A similar phenotype has been described in cucumber and named Es-1 and Es-2 (9).

None of the genes segregating in the RI Vedrantais x PI 161375 are linked (Table 2). Epistatic tests are necessary to establish the independence between Al-3, Al-4 and the other genes. In the 'Vedrantais' x PI 414723 population, we found a possible linkage between wf-2 and s-3, with a calculated genetic distance (2) of 28 cM Kosambi (7), and also between Me-2 and Ec (23 cM, Table 3). However, the probabilities for these two linkages were very near the threshold limit (p), and the small population used (63 RI) could result in a spurious linkage. Mapping with molecular markers will confirm or disprove these results.

Interestingly, we can explain some very important phenotypic differences between the 3 parents with a few key loci, six for PI 161375 and four for PI 414723. If one disregards the important traits for shape and flavor, the major distinctions between melon horticultural group may be the results of a few key loci that play significant roles in the morphological differences between each group (3).

The major genes described here are now being incorporated into the molecular linkage map of melon we are developing. Moreover, we are planning to map quantitative trait loci (QTL) for fruit characters in our two populations. We hope to better understand the general control and gene interactions determining fruit characters in melon. the common parent of the two populations will allow merging of the two maps to create an integrated map of melon (11). This will offer the melon community a useful tool for breeding. Other fruit-quality and/or morphology genes which segregate in other crosses will be included using a combination of bulked segregant analysis (10) and map merging. Our main objective is to map the major genes and QTLs defining fruit quality on an integrated reference map of melon.

Table 1. Genetic control of nine fruit characters in two recombinant inbred (RI) populations. The dominant character is listed first (*e.g..: orange/green, orange is dominant to green).

Character
Oberved frequencies
Theoregical segregation
X2 value
X2 Probability
Gene symbol
Reference
RI 'Vedrantais' x PI 161375

Flesh color

55:49
1:1
0.35
55%
gf-2
(6)
orange/green
Fruit abscission

80:23

3:1
0.59
44%
Al-3, Al-4
(15)
Abscission/non-abscission
.
Spots on the rind
52:47
1:1
0.25
61%
Mt-2
(4)
Absebce/presence
Placena number
45:62
1:1
2.14
14%
p
(13)
3/5
Sutures on the rind
50:56
1:1
0.34
56%
s-2
(1)
Absence/presence
RI 'Vedrantais x PI 414723
Mealy flesh
22:24
1:1
0.087
77%
me-2
(4)
crisp/mealy
Sour taste
22:24
1:1
0.087
77%
So-2
(8)
Sour/sweet
Empty cavity
29:27
1:1
0.071
79%
Ec
This work
Empty/full
Seed color
35:24
1:1
2.05
15%
Wt-2
(5)
Yellow/white
Sutures on the rind
28:28
1:1
0
100%
s-3
(1)
Absence/presence

Table 2. X2 values for independence of several fruit trait genes in the RI population 'Vedrantais' x PI 161375. Probability associated with the X2 value is shown in parentheses.

 
sp-2
p
s-2
gf-2
1.58 (66%)
1.38 (71%)
3.56 (31%)
sp-2
4.62 (20%)
1.43 (70%)
p
3.79 (28%)

Table 3. X2 values for independence of several fruit trait genes in the RI population 'Vedrantais' x PI 414723. Probably associated with the X2 value is shown in parentheses.

 
So-2
Ec
wt-2
s-3
me-2
2.76 (43%)

7.22 (6.5%)

d=21.9 cM

1.82 (61%)
0.26 (97%)
So-2
0.42 (93%)
2.18 (53%)
0.43 (93%)
Ec
2.47 (48%)

0.93 (82%)

wt-2

8.66 (3.4%

d=25.7 cM

Acknowledgement. This work was supported in part by Conseil Regional Provence-Alpes-Cote d'Azur.

Literature Cited

  1. Bain, M.S. and U.S. Kang. 1963. Inheritance of some flower and fruit characters in muskmelon. Indian J. Genet. Plant Breeding 23:101-106.
  2. Burr, B. and F.A. Burr. 1991. recombinant inbreds for molecular mapping in maize: theoretical and practical considerations. Trends in genetics 7(2):55-60.
  3. Dobeley, J., A. Stec and C. Gustus. 1995. Teosinte branched and the origin of maize: evidence for epistasis and the evolution of dominance. Genetics 141:333-346.
  4. Ganesan, J. 1988. Genetic studies on certain characters of economic importance in muskmelon (Cucumis melo L.) Annamalai University (India).
  5. Hagiwara, T. and K. Kamimura. 1936. Cross-breeding experiments in cucumis melo. Tokyo Horticultural School Publication.
  6. Hughes, M.B. 1948. The inheritance of two characters of Cucumis melo and their interrelationship. Proc. Amer. Soc. Hort Sci. 52:399-402.
  7. Kosambi, D.D. 1944. The estimation of map distances from recombination values. Ann. Eugen. 12:172-175.
  8. Kubicki, B. 1962. Inheritance of some characters in muskmelons (Cucumis melo). Genet. Polonica 3:265-274.
  9. Kubicki, B. and A. Korzeniewska. 1983. Inheritance of the presence of empty chambers in fruit as related to the other fruit characters in cucumbers (Cucumis sativus L.). Genetica Polonica 24:327-342.
  10. Michelmore, R.W., I. Paran and R.V.Kesseli. 1991. Identification of markers linked to disease-resistance genes by bulked segregant analysis: A rapid method to detect markers in specific genomic regions by using segregating populations. Proc. Natl. Acad. Sci. (USA) 88:9828-9832.
  11. Perin, C., L. Hagen, C. Dogimont, V. de Conto and M. Pitrat. 1998. Construction of a genetic map of melon with molecular markers and horticultural traits in Cucurbitaceae '98 Evaluation and Enhancement of Cucurbit germplasm, 1998. Pacific Grove, California. ASHS press: 370-376.
  12. Pitrat, MN. 1998. Gene list for Melon. Cucurbit Genetics Cooperative Report 21:69-81.
  13. Rosa, J.T. 1928. The inheritance of flower types in Cucumis and Citrullus. Hilgardia 3(9):233-250.
  14. Staub, J.E.,, F.C. Serquen and M. Gupta. 1996. Genetic markers, map construction, and their application in plant breeding. HortScience 31: 729-741.
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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;
send questions to T.C. Wehner; last revised on 15 December, 2009