Wide Hybridization in Plants pp. 294-300 (1960; English trans. 1962)

I. K. Maksimenko
Candidate of Biological Sciences
Turkmen Agricultural Research Institute*
*Turkmenskii nauchno-issledovatel'skii institut zemledeliya.

The world cotton assortment of types comprises large numbers of species and varieties possessing naturally colored fiber. G. Watt (1907) cites a whole series of cotton species, races and varieties with variously colored linter and fiber. Gossypium brasiliense Macf., which grows in Brazil and Peru, has a yellow-brown fiber. The fiber of another cotton growing in New Guinea is brown-red. G. Palmeri Watt, which grows in Mexico, has silky, deep red fibers. Colored fiber is also encountered in wild cotton species: G. Sturtii Mull., G. Schottii Watt, G. Mustelinum Miers, G. Darwinii Watt, G. Harknessii Brandegel (gray-brown fiber), G. Davidsonii Kellogg (gold colored), G. tomentosum Nutt (dark rust color), G. Stocksii Mast. (light brown) and G. punctatum Schum. et Thonn., which grows in the U. S. A., in Jamaica, Costa Rico, and Curacao, and also in Africa - in Senegal and Nigeria. In the U. S. A., colored cotton is known as brown or blue-green "Texas wool".

The Ceylon cotton G. obtusifolium Roxb. comprises forms with grey-green fiber and linter. Fibers of a gold-gray to brown coloration occur in the species G. Nanking Meyen, G. hirsutum L., G. herbaceum L., G. purpurascens Poir. and G. punctatum Schum. et Thonn.

Many investigators (N. M. Romanov, 1941; C. M. Conrad and L. Neely, 1941-1943, and others) have established that a fiber which has a natural green coloration contains up to 17% of waxy substances, whereas a colorless (white) fiber contains only 0.4 to 0.7%.

It is noteworthy that it is the cotton forms with naturally colored fibers that have mainly been used by foreign researchers for genetic investigations. From the available literature, it seems that until recently, these workers concerned themselves with questions of producing cotton varieties with naturally colored fiber.

In the U. S. S. R., plenty of samples of different cotton varieties with naturally colored fibers have been collected, in particular samples with dark brown to brown fibers. Breeding projects aiming at producing high-yielding cotton varieties with a colored fiber were started in 1938-1939. At the Central Breeding Station of the All-Union Cotton Research Institute, B. P. Straumal and Academician S. S. Kanash did breeding work on cotton with brown fibers. We began developing cotton with naturally colored, mainly green, fiber at the Turkmen Experimental Station of the All-Union Cotton Research Institute. At the same time, the color and technological properties of naturally colored cotton were studied (V. S. Fedorov, 1941, 1943; N. M. Romanov, 1941, and others).

Aims and methods of breeding. The breeding of cotton varieties with naturally colored fiber has aroused much attention, because natural fiber coloration is considerably more stable than any artificial dye, and because such fiber has a number of technological and economic advantages. The question has not only been to improve colored fiber (brown) cotton forms that exist in nature, but to create cotton plants with new color shades. These were also our breeding objectives at the Turkmen Experimental Station (at lolatan').

The Darwin-Michurin doctrine, which predicts the appearance of new features in wide crosses and the possibility of their accumulating and becoming fixed in the progeny by selection, has served as a theoretical basis in investigations on breeding for a new fiber color. In formulating a working hypothesis on the possibility of obtaining cotton forms with green fiber, we started from the assumption that the appearance of green linter on the seed is a new character which arises in an interspecific cross. If the green color has appeared in the linter of hybrid seed, it can, under adequate conditions, also appear in the fiber. This is because linter and fiber are both formed from the epidermal cells of the seed, though one is formed from the first, and the other from the second layer.

The examination of a large number of hybrid plants from interspecific cotton crosses (in 1939 more than two thousand plants from 12 combinations of interspecific crosses were examined) has shown that the green color of the linter varies considerably in intensity.

* Varieties 1708 I, 8517 I, 8427 and 36M belong to the species G. hirsutum L.; collection specimen 247 belongs to G. purpurascens Poir., and Pima to species G. barbadense L.
** Varieties 2 IZ and 1201 1 belong to the species G. barbadense L.

From the interspecific cross combinations (1708 I X 8517) X 247, (1778 I X 8427) X 247, 36 M2 X 247 and Pima X 36 M2*, we chose 24 plants for obtaining progeny. Ninety-three additional plants were chosen from the same combinations and from other interspecific crosses (2 IZ X 36 M2, 1201 I X 36 M2, 1201 I X 1708 I, and others)** in which only the linter was colored, while the fiber was white.

In the progeny of the selected plants an intensive process of form development could be observed. In every family there were plants which were markedly unlike each other in all characters (habit of the bush, leaves, bolls, bracts, flowers, etc.). The coloration of the vegetative organs varied in most plants of the hybrid families from green to dark red. In many families, more than half the plants showed various degrees of fiber coloration. The green fiber color became intensified in shade. This was observed, in particular, in the progeny of 24 plants whose linter was most intensely colored and in which there were even traces of coloring in individual fibrils on the micropylar end of the seed. In several other families, only single plants had a greenish fiber. The progeny of a plant that had been chosen from hybrids of the cross combination Pima X 36 M2 was outstanding for the intensity of the green coloration of the fiber. The progeny of this plant served as starting material for the subsequent breeding of new cotton forms and varieties with a colored fiber. Moreover, it was an object for the study of the form-creative process and for investigations of cotton hybrids with rudimentary, natural fiber coloration.

In later progenies, a lack of uniformity in the intensity of fiber color in individual plants was noted in certain families. Usually the fiber color in bolls of the lower branch layers was more intense than in those on higher branches. Also, there were plants in which fiber coloration varied in bolls of the same sympodial branch, or even in seeds within one boll (white and green fibers). It has been found that the pigment in the fiber only appears shortly before the bolls open, and that the fibers are white up to that time. Subsequently it was found that the external environment can have a varying influence on the fiber coloring of different forms after the opening of the bolls. In some cases, the coloration changes under the influence of climatic factors or becomes less intense in shade; in other cases it remains stable.

The appearance of character differences within individual cotton hybrids has been utilized in experiments aiming at the improvement of breeding methods. For instance, problems of how to make seed selections from a single plant in order to intensify certain characters have been solved. Seed collected from different parts of the plant and exhibiting different intensities of fiber coloration gave rise to different progenies; seeds with a dark colored fiber gave rise to more individuals whose fiber was of a deeper green, and there was less segregation in their progenies than in progenies from other seeds of the same plants whose fiber was light green in color. Further breeding brought out an even greater differentiation in the fiber color; new colors appeared which had not been met with previously, for instance, colorings with rudiments of blue, azure, cream-pink, grey and other hues. The new features which appear in the course of the formation of interspecific cotton hybrids with fibers of a natural green or other color, have been used for the study of hereditary changes in characters. Through such studies, breeding methods for obtaining cotton plants with naturally colored fibers can be improved.

The process of form creation in the cotton hybrids. Interspecific hybridization of cotton resulted in the appearance of a new character not encountered previously -- the green coloration of the fiber. Observations were started from the moment of its appearance on the development of this new character in the cotton plant. The study of the form-creative process over a number of generations concentrated on a plant, from the cross combination Pima X 36 M2, which showed traces of green coloration of the fiber. In the first-generation progeny from this cross there were 91 plants, of which 66 showed a certain degree of fiber coloration. The seed of each plant with colored fiber was sown in a separate batch. In the second generation 2,010 plants were obtained, of which 638 had a more darkly colored fiber; these were put aside for further study. The seed of each of these plants was sown separately in the following year, and 25,600 plants were raised. Our detailed study of the starting plant and three generations of its progeny have confirmed the intensive form development process taking place in the hybrids. In the progeny of one starting plant with rudiments of green fiber coloration, forms with bluish, azure and cream-pink colored fibers began to develop; through directed selection, the green fiber coloring became darker. In these hybrids, variability was also observed in other morphological and economic characters. In the analysis of three hybrid generations of family No. 628, the development of natural fiber coloration, staple length and lint output, the size of bolls and seed, and other characters could be observed in a large number of plants (15 plants in the first generation, 215 in the second, and 1,303 in the third). These investigations showed that any fiber coloring, as well as white fiber, can form in plants whose vegetative organs (leaves, stems) are green, red or intermediate in color. Fiber coloring is not dependent on the shape of the bush, the size and shape of the leaves and bolls, or the color of the petals, anthers, etc.

The hybrid analysis of these plants has helped us to determine possible rules for selection in cotton plants. Some authors (N. N. Hull, 1934; S. C. Harland, 1939; M. P. Singh, 1941; Z. Ninston, 1943) have stated that the green fiber coloring is correlated with a low percentage of lint output. We have found no such correlation. The lint output in green-fiber hybrids varies between 18 and 38%.

Experience and practice have confirmed the fact that it is possible to create cotton plants with a natural green coloration and heightened lint output. This is achieved by multiple selection. If selection is carried out in the desired direction for three generations, constant green-fiber families with an increased lint output can be produced. Investigations have shown that the thousand-seed weight in green-fiber hybrids varies between 80 and 160 g, and that the lint output is not dependent on seed size.

The weight of the raw boll is extremely variable in green-fiber hybrids. An analysis showed that the largest number of segregating hybrids has a raw-boll weight of 3.5 to 4.5 g; in single cases, bolls with a raw weight of 6 g or more were encountered. By selecting plants with the largest bolls, the weight of the raw boll can be increased in green-fiber forms of cotton. Lint length in the hybrid plants varies between 25 and 42 mm. Constant families of cotton with naturally colored fiber of various length can also be created through selection.

The pattern on which the basic characters in colored-fiber cotton (such as lint length and output, boll size, etc.) are formed and modified, could be determined by observation. With the aid of the rules established, selection could be directed to intensify and fix these characters in cotton hybridization.

A study of the inheritance of different fiber colors in cotton has shown that the green color is the most easily fixed in the progeny. As a rule, it is difficult to fix bluish, cream-pink and azure colors of different intensities and shades.

During the investigations, cases of neoplasm were observed in the cotton plants. For instance, plants with six-valved capsules and four large bracts were detected among the hybrids (family 5, second generation). These same characters had not been present in the starting forms.

The study of cell variability within the cotton plant is of great interest. We have already mentioned the plants encountered in our experiments, in which different bolls of the same plant had fibers of different colors. By selecting seed from capsules in which the green fiber color was more pronounced, the development of cotton forms with a darker green fiber could be accelerated. The selection of seed from different parts of one lobe of the same capsule has an even more startling effect. Seed taken from the lower part of the lobe, in which the fiber is usually of a darker shade, gave rise to progenies containing plants in which the fiber was more evenly colored than in plants grown from seed from the upper part of the same lobe.

The appearance of the green fiber color is seen to be linked to a definite age of the bolls. The fiber in green-fiber cotton is white up to a boll age of approximately 35 to 40 days; green pigmentation only appears before the bolls open. In cotton with a dark brown to brown fiber, the coloring appears much earlier.

Certain properties of the green coloring of the fiber were studied in special investigations, and it was found that the green color can have a varying stability on exposure to particular external environmental factors. In some cases, the green color may change its shade considerably under the influence of these factors (it becomes lighter, more brownish, etc.); in other cases it undergoes no change. Forms of the latter group are more valuable where the aim is to obtain cotton with a resistant fiber color. The majority of cotton forms with a dark brown fiber, particularly G. barbadense L., have a somewhat different reaction to the environment. As a rule, the color of their fiber darkens after the opening of the bolls.

The differences observed in the stability of green and dark brown fiber color were utilized in hybridization. In crosses between forms with a brown fiber and forms with a green fiber, the color-appearance traits which characterize the starting forms are preserved in the obtained hybrids. As a result, plants with brown-green fiber, which became darker after the opening of the bolls, were obtained.

Crosses between the newly created plants with colored, mainly green, fibers and representatives of various species of white-fiber cotton, and also intercrosses between colored-fiber cottons, showed that segregation is less marked in the progeny from crosses between green-fiber hybrids and varieties of G. hirsutum L. than in that from crosses between these hybrids and varieties of G. barbadense L.

Segregation of fiber coloring has been observed in progeny from intercrosses between different green-fiber hybrids; the fibers of segregants were white, bluish, azure, and other shades.

The economic properties of newly created cotton forms with a naturally colored, green fiber were improved by hybridizing them with white-fiber forms.

Breeding results. Investigations show marked differences between the first green-fiber cotton lines derived from one hybrid plant of the cross combination G. hirsutum L. X G. purpurascens Poir., both morphologically and in economic characters. In the coloration of vegetative organs there was a transition from green to dark red, and there were also great differences in the shape of the bush, size and shape of the leaf, branches and bolls, etc. There were also marked differences in quickness of ripening, boll size, productivity, staple length and lint output, etc. The general shortcoming of the obtained lines is the low lint output (20 to 25%). The fiber coloring in most of these first lines was green, but of a weak and uneven shade; the fiber was of a low strength, which also decreased its value.

Through further breeding by backcrosses and directed selection, a number of lines were obtained with a deeper and more even green color of the fibers, increased output, and somewhat improved technological fiber qualities. New cotton lines with a brown-green fiber were also produced; some of them gave high yields of raw cotton (higher than those of the standard variety 2 IZ), and their lint was of a satisfactory length.

* Value specifying the degree of fineness of the fiber.

By crosses and multiple directed selection, the existing cotton lines with a colored fiber were improved, and new lines with high technological index ratings were developed. Fiber yield in green-fiber lines was increased. While lint output in the earliest lines was no more than 20 to 25%, an output of 28 to 30% was arrived at in lines produced subsequently. The raw weight per boll was increased to 5.5-6 g, the technological qualities of the lint were somewhat improved, a better seasoned and stronger fiber was obtained and the metrical number * was reduced. Fiber strength was increased to withstand a pressure of 4 and even 5 g, which was an improvement over the fiber of the earliest lines, which tore at a pressure of 2.5 to 3 g.

From this material, line 7631 was obtained, which yields the darkest, most evenly colored green fiber. This line was grown on tens of hectares, and the first tons of naturally colored, green cotton were obtained; these were processed by textile plants into thousands of meters of fabric for experimental purposes.

** Moskovskii tekstil'nyi institut.
*** Tsentral'nyi nauchno-issledovatel'skii institut khlopchatobumazhnoi promyshiennosti.
**** Tashkentskii tekstil'nyi kombinat.
***** Ivanovskii nauchno-issledovatel'skii institut tekstil'noi promyshlennosti.

The naturally colored fiber was studied in the laboratories of the Moscow Textile Institute**, the Central Research Institute of the Cotton Industry*** the Tashkent Textile Group****, and the Ivanovo Research Institute of the Textile Industry*****. As a result, it was found that naturally colored fiber can be activated and has the binding properties of certain chemical reagents (iron salts, etc). The color of the lint can be darkened by the most simple treatments (by soap solution, caustic soda). It was also established that the natural coloring of the lint fully withstands washing.

The naturally colored lint can be used in the mixed cotton industry for the production of plain-textured and combed fabric it is also suitable for mixtures with wool, the production of "mouline" yarn and other textile products.

On the basis of the experience gained and the breeding material created, the following points can be recommended:

1. The improvement of economically valuable traits and the technological qualities of the fiber in existing colored-fiber cotton forms by selection:

2. The intensification of hybridization to produce new starting material for breeding high-yielding cotton forms with various stable fiber colors. Stress should be laid on the improvement of the technological qualities of the fiber, in particular, on the development of a more-mature and stronger fiber with a reduced metrical number. Work should be done on creating cotton forms with new fiber colors of a more solid and uniform deep shade;

3. Cotton forms with a brown or green fiber should be introduced into hybridization by every possible means; this might ease and accelerate the breeding of cotton plants with a naturally colored dark fiber.

As a result of breeding projects with cotton with a naturally colored fiber, many factual data have been accumulated which confirm the correctness and actuality of Michurin's doctrine of plant hybridization, and demonstrate that new varieties satisfying practical needs can be created within a relatively short time.

The following conclusions can be drawn:

1. Wide crosses (interspecific) lead to profound changes within the organism and often to the appearance of entirely new characters not present in the parents. Forms exhibiting such new characters, e. g., a naturally colored fiber of a green, bluish, azure or other shade, or six-valved bolls, four bracts, red leaves and stems, etc., were obtained from crosses between white-fiber cottons, such as G. hirsutum L. X G. purpurascens Poir., G. barbadense L. X G. hirsutum L., and others.

2. In the early stages of work, new characters are often very weakly expressed in the cotton hybrids. By selecting forms in which the new traits are most markedly exhibited, properties that are useful for practical purposes can be accumulated and fixed in the course of some generations. In this manner, new forms and lines of cotton with a colored fiber were obtained from hybrid plants in which only rudiments of these characters were present. The appearance of a new character in the cotton plant (the green color of the fiber) is the result of the form-creative process in interspecific cotton hybridization.

3. Many hybrid plants possess variable cell properties; the same character may be observed to vary in a single plant. Variations in fiber color (white and green) were noticed within the same plant, and even within the same lobe of the boll.

These observations were utilized for the working out of a method of seed selection within single plants. By selecting individual seeds within the plant, constant forms of cotton with a naturally colored, dark green fiber could be obtained more speedily.

4. The process of appearance and the properties of different pigments (green, brown, etc.) in the cotton fiber were studied. This aided the production, by hybridization, of economically valuable cotton forms with a naturally colored fiber and resulted in the creation of forms with a brown-green fiber of a dark, stable color.

5. It has been established that the fiber of naturally colored cotton can be activated and has the binding properties of the most common chemical reagents. This facilitates the modification and stabilization of the fiber's natural color shade by simple chemical treatments.

6. Hybridization has revealed rules for the development of different characters (length and output of the lint, boll size, etc.) in combination with the fiber coloring, and good data have been gathered as to the direction in which selection should be effected in order to improve this or that character of the cotton plant.

7. For the first time in Soviet breeding practice, new constant lines and varieties of cotton with a naturally colored fiber of a green or brown-green shade have been created.