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The Journal of Heredity 1942:33(4):144-152
© 1942 The American Genetic Association 33:144-152

research-article

POLYPLOIDS IN THE GENUS CUCUMIS*

Preliminary Account

OVED SHIFRISS{dagger}

Department of Plant Breeding, Cornell University Ithaca, N. Y.

Abstract

  1. Colchicine-induced tetraploids of the cucumber, Cucumis sativus, exhibit, iu general, the expected gigantic features. However, the accentuated serration of the leaf margin is their most distinguished peculiarity.
  2. It is interesting that only in the octoploid or higher polyploid forms do we find a pronounced difference in the size of the corrolla between staminate and pistillate flowers borne on the same plant.
  3. In the succeeding selfed generations of the tetraploid population maternal diploids, typical mutants and segregates for plant vigor, size, and color of fruits, were recovered.
  4. The frequency of stomates per unit area is decreased by chromosome doubling but the frequency for a given number of epidermal cells is the same in both the tetraploid and diploid forms.
  5. The size of the chloroplasts and the number of chloroplasts per unit of cytoplasm are not significantly different in the diploid and the tetraploid forms.
  6. The dimensional change in fruit shape brought about by polyploidy depends apparently on the initial genie patterns involved, the level of chromosome multiplication, and in some cases, on the physiological reaction of the tetraploid plants. The type of change in fruit shape may be interpreted on the basis of modified genie action in the genetically new systems produced by chromosome doubling.
  7. The tetraploid cucumbers possess new physiological norms. They actually have a reduced range of ecological adaptation and are at least as susceptible to most cucurbit diseases as are the diploids.
  8. Fertility in the cucumber is affected by environmental factors. Sterility as a character is accentuated by chromosome doubling due to the physiological reaction of the tetraploid plants and the initial increase of pollen and egg abortion. The interaction of several possible factors is discussed.
  9. Intercrosses between diploids and tetraploids are extremely difficult to obtain, suggesting that once they are established the tetraploids represent a distinctly isolated population.
  10. It has been demonstrated that spontaneous tetraploids do appear at a low frequency in the cultivated cucumber. However, a natural tetraploid population can hardly exist under the present environmental conditions.

Several autotetraploid vegetables (beet, broad bean, cabbage, cucumber, lettuce, melon, potato tomato, squash, etc.) have been produced by various workers. However, these forms do not represent, at the present time, new types that are commercially superior. They are of recent origin and it is possible that marked improvement may be achieved by breeding.


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