Monoecious Sex Expression in Muskmelon, Cucumis melo L.

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Cucurbit Genetics Cooperative Report 3:32-33 (article 18) 1980

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:

  1. Foster, R. E. 1968. F1 hybrid muskmelons. V. Monoecism and male sterility in commercial seed production. J. Heredity 59: 205-207.
  2. More, T. A. 1977. Studies on heterosis in muskmelon (Cucumis melo L.). Ph.D. thesis, Indian Agricultural Research Institute, New Delhi, India.
  3. 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.
  4. Sharma, J. C. 1975. Genetical studies in muskmelon (Cucumis melo L.). Ph.D. thesis, Indian Agricultural Research Institute, New Delhi, India.
  5. Wall, J. R. 1967. Correlated inheritance of sex expression and fruit shape in Cucumis. Euphytica 16: 199-208.