Cucurbit Genetics Cooperative Report 4:26-28 (article 14) 1981
Association of Sex Form with Fruit Shape in Muskmelon
(Cucumis melo L.)
N. N. Shinde* and V. S. Seshadri
Division of Vegetable
Crops and Floriculture, Indian Agricultural Research Institute,
New Delhi-11012, India
An attempt was made to verify the observations of Rosa
(2), Kubicki (1), and Wall (3) regarding the extent of association
between monoecious sex expression and oblong fruit shape
and of andromonoecious sex expression with round fruit shape.
Further, it was possible to study the existence of linkage,
if any, of hermaphroditic sex expression and the extent
of association of flat fruit shape with any of these sex
forms. In these studies, the fruit shape was characterized
as flat, round and oblong on the basic of shape index (polar diameter/equatorial diameter) of < 1.0, around
1.0 and > 1.0 respectively.
In F2 populations derived from monoecious x andromonoecious
crosses involving plants with oblong and round fruit, linkage
was detected and estimated in monoecious-1 x andromonoecious-2
in coupling phase and monoecious-4 x andromonoecious-1 in
repulsion phase. The recombination fraction for the former
was 0.310 ± 0.072 in straight combination and 0.247 ±
0.068 in reciprocal combination, whereas in monoecious-4
x andromonoecious-1, it was 0.699 ± 0.084 indicating absence
of linkage in the reciprocal combination. In andromonoecious-2
x monoecious-3 in coupling phase, no linkage was detected.
In the cross monoecious flat x andromonoecious round, linkage
was detected in the reciprocal cross with a recombination
fraction of 0.643 ± 0.080, while no linkage was detected
in monoecious flat x andromonoecious oblong. The recombination
obtained in both coupling and repulsion phase was quite
high, 24 to 31% and 63 to 69%, respectively, indicating
thereby very loose or no linkage between sex of the plant
and fruit shape. The p-value obtained was more than 0.50
viz. 0.699 ± 0.084 and 0.643 ± 0.080 and they were within
the range of 5% standard error. This is indicative that
there was no linkage.
These observation indicate only loose linkage of oblong
and round shapes with monoecious and andromonoecious sex
types. Two possibilities are indicated. The genes for monoecious
and andromonoecious sex forms appear to be located on different
chromosomes or a second possibility is that genes for fruit
shape are located in the same chromosome where genes for
sex are present. The spatial distance between these two
loci could not be estimated. Data clearly indicate that
the chances of recombinations through crossover are comparatively
high and linkage in coupling phase can at best be termed
as a loose one. However, the flat fruit shape did not seem
to have any particular kind of association with any of the
two sex forms as did those of oblong and round fruit shapes.
No linkage was detected in the round x oblong crosses involving
andromonoecious (Ga) and hermaphrodite (ga) parents differing
at the G locus.
In a monoecious (GA) x hermaphrodite (ga) cross, the segregation
of sex is assumed to be mainly on two major genes (A
and G) and fruit shape on one gene basis.
In a hermaphorodite-2 and monoecious-3 cross representing
parents in coupling phase, linkage with A gene
was detected with a recombination fraction of 0.358 ± 0.057
and no linkage was detected between G gene and
fruit shape. In the repulsion phase, the recombination fraction
was 0.649 ± 0.067 for A gene and no linkage was
detected with G gene in a cross between monoecious-4
x hermaphrodite-1. Similarly, no linkage was noticed in
monoecious-2 x hermaphrodite-1 involving parents with flat
x oblong fruit shape, either with the A or G
loci.
On the basis of these results obtained in three different
sets of crosses, it can be concluded that there appears
to be very loose linkage between A gene with oblong
fruit shape and recessive a gene with round fruit
shape. However, there is no linkage with G gene
as has been noted from the nonsignificant X2 values for
linkage in monoecious x hermaphrodite and andromonoecious
x hermaphrodite crosses. Flat fruit shape was also not found
to be associated with any of the sex forms.
Wall's observation (3) that muskmelon fruit shape was determined
by single gene with incomplete dominance and it was linked
in coupling phase with genes for sex forms were not corroborated
by these results. High recombinant fraction obtained in
the present studies clearly ruled out the possibility of
pleiotropy suggested by Rosa (2). Results of Kubicki (1)
and Wall (3) were related to the cultivated varieties of
New World Origin and hence an impression was gained of the
possibility of sex linked inheritance. The present studies
gave credit to some kind of loose, and probably chance,
association of fruit shape in monoecious and andromonoecious
sex forms and it might have been due to unconscious selection
during domestication and evolution of present day cultivars.
There is clear evidence against the hypothesis of sex linked
inheritance with fruit shape.
Literature Cited
- Kubicki, B. 1962. Inheritance of some characters in
muskmelon (C. melo L.) Genet. Polon.
3: 265-274. (Plant Breeding Abs. 1964, no. 1162).
- Rosa, J. T. 1928. Inheritance of flower types in Cucumis
and Citrullus. Hilgardia 3: 235-250.
- Wall, J. R. 1967. Correlated inheritance of sex expression
and fruit shape in Cucumis. Euphytica 16: 199-208.
* Presently at the Department of Horticulture, Marathwada Agricultural University, PARBHANI-431402, India.
