Cucurbit Genetics Cooperative Report 3:32-33 (article 18) 1980
Monoecious Sex Expression in Muskmelon, Cucumis melo
L.
T. A. More, V. S. Seshadri and J. C. Sharma
Indian
Agricultural Research Institute, New Delhi-110012, India
Interest in monoecious sex expression in muskmelon is of
recent origin and has increase because of the obvious difficulties
associated with emasculation in the common andromonoecious
cultivars of muskmelon. Seed of F1 hybrids has been limited
in muskmelon in some countries. Even genetic male sterility
has not simplified the techniques of hybrid seed production.
Monoecious parents for F1 hybrids provide a partial answer
to the difficulties met with in production of F1 hybrids.
Foster (1) was the first to highlight their use in exploitation
of heterosis.
In the course of investigations on heterosis at Indian
Agricultural Research Institute, New Delhi (India), a monoecious
segregate was isolated (4). This genetic stock had oblong
fruit shape and was designated M1. The line was tested as
a female parent in studies on combining ability and showed
good general combining ability (GCA) effects for early yield, total yield, and fruit
weight. Concurrently, further studies were initiated to
improve the fruit shape to round in this genetic stock.
This led to the development of M2. This line had round fruit
shape. It was tested in combining ability studies and it
was observed that it had good GCA effects for earliness.
In order to improve the stocks further, more crosses were
made with good quality andromonoecious cultivars. Another
stock, M3, with slightly oblong shape and superior fruit
quality was developed (2). It showed good GCA effects for
fruit number, fruit weight, total yield per plant, TSS content
and flesh proportion. In another sister line, M4, the fruit
shape was round. Two backcrosses to an andromonoecious recurrent
parent followed by two generations of selection for monoecious
sex form and better fruit quality brought forth true breeding
lines of M3 and M4. The ease with which these desirable
recombinants were identified points out that sex and fruit
shape in muskmelon are not as tightly linked as was thought
before (5), and it is more of a chance association. We propose
that in the evolutionary process and domestication of varieties
in muskmelon, andromonoecious sex forms were established
because of possibly human preference to round shape. Invariably
monoecious varieties with oblong fruit shape probably were
eliminated with the result that most of the cultivars, except
those in Central Asia, are andromonoecious. This proposition
is under investigation by studies on the existence of linkage,
if any, and its estimation.
Studies were made on pollination and fruit set with M1
genetic stock comparing it with three andromonoecious varieties.
In 1972 and 1973, it was observed that mean fruit set by
controlled hand pollination using M1 genetic stock as female
parent was 34.84%, while in the three andromonoecious varieties
fruit set ranged from 10.05 to 23.05%. Fifteen andromonoecious
varieties (as the male parent) were crossed onto M2 and M3 and average
fruit set from hand pollination was 28.54% with M2 as a
female parent and 41.62 % with M3 as a female parent. These
results bring out the usefulness of monoecious forms in
muskmelon in hand pollination.
In order to test the desirability of these stocks for hybrid
seed production under open-pollinated conditions, the M1
line was treated with ethrel (2 times at 200 to 250 ppm). The first
five flowering nodes bore pistillate flowers and then sex
expression reverted to staminate flowers (3).
Literature Cited:
- Foster, R. E. 1968. F1 hybrid muskmelons. V. Monoecism
and male sterility in commercial seed production. J.
Heredity 59: 205-207.
- More, T. A. 1977. Studies on heterosis in muskmelon
(Cucumis melo L.). Ph.D. thesis, Indian Agricultural Research Institute,
New Delhi, India.
- More, T. A. and V. S. Seshadri. 1975. Response of different
sex forms in muskmelon (Cucumis melo L.) to 2-chloroethylphosphonic
acid. Vegetable Sci. 2:37-44.
- Sharma, J. C. 1975. Genetical studies in muskmelon (Cucumis
melo L.). Ph.D. thesis, Indian Agricultural Research Institute, New Delhi,
India.
- Wall, J. R. 1967. Correlated inheritance of sex expression
and fruit shape in Cucumis. Euphytica 16: 199-208.
