OTS., 60(51030): liv-lvii (1961)
Published by National Science Foundation and the Department of Agriculture

The Influence of Grafting on Seed Progeny and on the Segregation of Hybrids in the Second Generation
Anton Ramanavich ZHebrak

The grafting of genetically pure strains of pea does not exercise any influence on the respective graft components nor on the hybrid seeds /1-4/. There was therefore no reason to assume that the influence of grafting would become apparent in any way in the second hybrid generation arising from the seeds [of grafted plants]. In order to verify the correctness of this assumption, we undertook a thorough study of the seed generation from various graft combinations. The results of this study are reported in this communication.

Seeds resulting from self or cross-pollination of grafted plants belong to the first hybrid generation, and the plants developing from them will bear seeds that belong to the second hybrid generation. Segregation occurs in the plants arising from the latter, and the development of dominant and of recessive characters, as well as the numerical ratio between the various segregating classes, can be studied in them.

Experiments on studying the influence of grafting on the [first] seed-grown generation, and on segregation of hybrids in the second generation, were carried out in 1950. Part of the plants was grown in the botanical garden of the Moscow Institute of Pharmacy; the remainder was grown in containers on a balcony. Several variations of experimenting with grafting and with crossings were carried out. They are described in the following:

Trial batch 1. (Control). [Plants from seeds of] ungrafted yellow Victoria. This batch was introduced in order to verify the purity of the starting material, and serve to check the absence of contaminating cross-pollinations prior to the experiment. Control plants were grown under the same conditions as experimental plants, that is, in containers on a balcony and in the open ground. When harvested, the plants grown under these different conditions were recorded separately. As far as the height of the stem and the development of hereditary characters are concerned, all the control plants proved constant. The height of the stem of 32 recorded plants grown in the open ground varied from 113 to 200 cm, with an average of 164 cm. The number of internodes in the same plants varied from 17 to 30, with an average of 23. The plants grown in containers were somewhat shorter; the height of their stems varied from 95 to 140 cm. The number of internodes varied from 17 to 22. The seeds of ripe peas were round and yellow; unripe ones were greenish.

Trial batch 2. First generation hybrid plants obtained from seeds of ungrafted Yellow Victoria, pollinated by Miracle of Lyon. The height of the stem varied from 158 to 195 cm, with an average of 171 cm. The number of internodes varied from 23 to 25, with an average of 24. Segregation occurred in all hybrid plants, each of which produced four classes of differently shaped and colored seeds. Altogether the experimental plants produced a total of 452 seeds. Of these 249 were round and yellow, 86 round and green, 82 wrinkled and yellow, and 35 wrinkled and green. The theoretically expected figures for these classes are 254,25; 84,75; 84,75; 28,25.

Trial batch 3. Plants obtained from seeds of Yellow Victoria grafted on Miracle of Lyon, by self-pollination. All the plants were of similar appearance and approximately uniform as far as height of the stem was concerned. The height of the stem varied from 150 to 185 cm, with an average of 164 cm. The number of internodes varied from 21 to 27, with an average of 24. Part of these plants were grown in containers on a balcony. the height of the stem of plants grown in containers varied from 122 to 138 cm. The number of internodes varied from 20 to 22. All plants of this batch formed seeds typical for the variety i.e., round and yellow.

Trial batch 4. First generation hybrid plants obtained from seeds of Yellow Victoria grafted on Miracle of Lyon, and pollinated by Miracle of Lyon. This was one of the most interesting batches. All the plants of this batch had stems of uniform height and were similar in all other characters. The height of the stem varies from 150 to 183, with an average of 169 cm. The number of internodes varied from 22 to 26, with an average of 23. Part of these plants was grown in containers on a balcony, and had a number of internodes varying from 18 to 20. All the plants showed segregation. Soil-grown plants yielded a total of 1,201 seeds, and container-grown plants 41, so that there were altogether 1,242 seeds. Of these, 696 were round and yellow, 243 round and green, 230 wrinkled and yellow, and 73 wrinkled and green. The theoretical figures for these classes are: 698,62; 232,87; 232,87; 77,62.

Trial batch 5. Plants from seeds of Miracle of Lyon, self-pollinated (control). This control was also introduced for establishing the homogeneity of the material. All plants, whether grown in soil or in containers, proved to be constant and fairly uniform. The height of the soil-grown plants varied from 75 to 91 cm. The number of internodes varied from 18 to 24. The seeds were typical of the variety in form and color.

Trial batch 6. First generation hybrid plants obtained from seeds of ungrafted Miracle of Lyon, pollinated by Yellow Victoria. All plants were uniform. The height of the stem varied from 158 to 239 cm, with an average of 188 cm. The number of internodes varied from 23 to 29. When comparing the height of the stem of the hybrids with that of the stems of the parent plants, the tall stem of Yellow Victoria was found to be dominant over the short stem of Miracle of Lyon. Moreover the hybrid shows heterosis. All the hybrid plants showed segregation according to both pairs of allelomorphic factors, with the appearance of four classes of seeds. Altogether the experiment here described yielded 686 seeds. Out of these 374 were round and yellow, 124 round and green, 145 wrinkled and yellow, and 43 wrinkled and green. Theoretically expected figures for these classes are: 387; 129; 129; 43.

Trial batch 7. Plants grown from seeds obtained from Miracle of Lyon grafted on Yellow Victoria, by self-pollination. By their outward appearance all plants in the batch were uniform. The height of the stem varied from 55 to 83 cm, with an average of 71 cm. The number of internodes varied from 17 to 23. All the seeds yielded by plants grown in this experiment had the appearance typical for this kind: a wrinkled shape and green color. There was no difference whatsoever between the seeds obtained from this experiment and seeds of ungrafted control plants.

Trial batch 8. [First generation] hybrid plants obtained from seeds of Miracle of Lyon grafted on Yellow Victoria and pollinated by Yellow Victoria. Part of the plants was grown in soil, and part in containers on a balcony. Hybrid plants of both groups were absolutely identical in their exterior aspect. Those grown in containers were less developed and had shorter stems. Those grown in the open ground had a stem varying from 174 to 210 cm in length, with an average of 183 cm. The number of internodes varied from 23 to 26. All hybrid plants segregated as regards shape and color of the seeds. Altogether this experiment yielded 357 seeds. Out of these 212 seeds were round and yellow, 69 round and green, 61 wrinkled and yellow, and 15 wrinkled and green. Theoretically expected figures for these classes are: 200, 25; 66, 75; 66, 75; 22, 25. When taking into account only one pair of characters, namely, the color of cotyledons, there were 273 yellow and 85 green seeds. Theoretically expected figures for these classes are: 267; 89.

Besides these basic variations of experiment, data were also recorded for the second generation of two additional minor batches.

Trial batch a. First generation hybrid plants obtained from seeds of ungrafted Miracle of Lyon, pollinated by Yellow Victoria that had been grafted on Miracle of Lyon. Altogether 3 hybrid seeds were obtained, all of which germinated and produced three plants. They were all grown in containers on a balcony, and had a stem height of 150, 150 and 156 cm respectively. The number of internodes was 18, 19 and 20 respectively. The height of the stem of control plants of Yellow Victoria grown under the same conditions was from 95 to 164 cm. The number of internodes was 17 to 22. The height of the stems on control plants grown in containers of Miracle of Lyon on a balcony varied from 45 to 58 cm; the number of internodes varied from 15 to 20. The diameter of the hybrid seeds of the first generation in this batch was 6,25 mm. Their total weight was 0.6542 g, i.e., average weight of a single hybrid seed was 0.2180 g. A single seed of Yellow Victoria of the same diameter has approximately the same weight.

All hybrid seeds showed segregation in the second generation, and formed four classes of seeds. Altogether there were 47 seeds, of which 19 were round and yellow, 10 round and green, 15 wrinkled and yellow, and 3 wrinkled and green. Three plants grown in containers yielded only for seeds, and for this reason the numerical ratio of seeds did not approach the theoretically expected figures. When recording segregation according to color characteristics, we obtained 34: 13. The theoretically expected figures for these characters are: 35,25 and 11,75.

Trial batch b. Plants obtained from the seeds of a Yellow Victoria shoot which sprouted below the grafted scion of Miracle of Lyon. Here seeds of the Yellow Victoria shoot were developing under the influence of Miracle of Lyon. All experimental plants were uniform in their outward aspect and yielded absolutely uniform seeds. The height of the stem varied from 155 to 180 cm, while the number of internodes varied from 25 to 28.

As the result of a thorough study of the seed generation from graft combinations of pure strains of pea, and of their hybrids, we arrived at the following conclusions:

1) The grafting of constant (homozygous) lines had no influence whatsoever on hereditary characters.

2) The degree of dominance or of recessiveness in the first and second generation was not altered under the influence of grafting of strains with dominant characters. This applies to the grafting of strains with dominant characters on those with recessive characters, and vice versa.

3) The correlation between dominant and recessive forms during segregation of hybrids in the second generation remained unchanged under the influence of grafting on respective allelomorphs.

4) The segregation of hybrids showed no deviations as a consequence of alteration of nuclear structure during meiosis under the influence of grafting.

Academy of Sciences of BSSR and The Moscow Institute of Pharmacy
Received for publication 6 April, 1955