Studies on Interspecific Hybrids in the Genus Solanum

Abstract

I Solanum integrifoloium POIR. ×S. Melongena L.
1. A hyprid was obtained by crossing between Solanum integrifolium and S. Melongena, but the reciprocal crossing was unsuccessful.
2. The F₁ hybrid is distinctly more vigorous than either parental form. It shows a greater resemblance to S. integrifolium than to S. Melongena, except that the purple plant color of S. Melongena is dominant over the green of S. integrifolium.
3. Under normal conditions the hybrid produces numerous short swigging roots on the lower part of the shoot, like in Lycopersicum esculentum. However the writer has never seen this characteristic in the parental forms.
4. Although flowering profusely, the hybrid was proved to be almost completely male sterile, producing a few emptied pollen grains in the anther. Likewise the ovules are almost completely sterile.
5. After about the middle of September, small seedless fruits are produced. It seems pro-bable that the ovaries of the hybrid grow into parthenocarpic fruits owing to the growth in-hibiting action of the lower temperature in the season.
6. As already known, the haploid chromosome number was observed to be 12 in both S. integrifolium and S. Melongena. The meiosis in PMC of the hybrid shows no irregularities up to the liberation of the microspores from the tetrad (Fig. 2-10). Following liberation the mi-crospores begin to disintegrate and the majority of them entirely degenerates, until a few abortive pollen grains are found in the anther (Fig., 11-17, 18, and 19-21).
7. In the 1934 to 1940 season it was proved that the F, hybrid produces extremely few seeds under favorable conditions.
8, In the later generations (F₂-F₄), both the S. integrifolium-like plants and the F₁ hybri-d-like plants are recovered, but no plants which resembled S. Melongena are secured
9. The progenies show the considerable variation in fertility ranging from complete ste-rility to complete fertility. The degeneration of pollen grains is brought about by the same process as that of the F₁ hybrid.
10. A few abnormal plants appeared in the later generations of the hybrid. The plants.are very dwarfed (about 40 cm in height) and less vigorous than their normal plants, anfl pro-duce no fruits, whatever. At first it was expected that they were likely abnormal plants, ha-ving aberrant chromosome numbers. While cytological study proved that this expectation is not the case, but the dwarf plants are also diploid.
II Solanum Melongena L.×S. ovigeruin DUN.
The F₁ hybrid of Solanum Melongena with S. ovigeruin is completely fertile. The haploid ch-romosome number of S. ovigerum is 12, as already known. The meiosis in PMC of the hybrid
is perfectly normal (Fig. 25-26). In the variety of S. Melongena used in the experiment the skin color of fruit is dark purple and the flesh color of fruit is light green. In S. ovigerum, on the other hand, both skin color and flesh color are white. The F₁ is dark purple skin (light greenflesh), and the F₂ is in the ratio 9 dark park purple skin (light green flesh): 3 violet skin (white flesh): 3 green skin (light green flesh): 1 white skin (white flesh). In this-case the genetic behavior of the hybrid was proved to be similar to the inter-varietal hybrids of S. Melongena.
III Solanum integrifoli'um Pore.×S. ovigerum Dun.
The hybrid between S. integrifoliuin and ovigerum shows a general similarity in behavior to the hybrid between S. integrifolium and S. Melongena. Hence no great detail will be gone into in the present description. (Ibaraki-tyo, Mishima-gun, Osaka-hu, Nippon)