Soviet Plant Physiology pp. 38-45 (1958)
INVESTIGATION OF THE INFLUENCE OF THE MENTOR ON FORMATION OF HYBRID SEEDLINGS
AND ITS DEPENDENCE ON THE POSITION OF THE GRAFT IN THE CROWN

M. D. Kushnirenko and E. T. Shtin
I. V. Michurin Central Genetic Laboratory, Michurinsk

Developing I. V. Michurin's teachings concerning the mentor, Soviet investigators have tried to increase its effect by considering from which part of the tree to take cuttings and grafts, and how and on which trees to graft them [1, 2, 3]. Great attention has been given to the state of the hybrid seedling which is to be developed.

I. V. Michurin showed that hybrid seedlings in their development from the seed to the adult state change in morphological characteristics from the wild form to that of the cultivated variety.

Graded or metameric heterogeneity of biological, physiological, biochemical and morphological characteristics is represented by numerous data of the literature [4-12]. A large part of these papers is connected with study of the levels of leaves along the shoot, location of the fruit-bearing organs of annual plants, and metameric variety in quality of separate branches of perennial plants. Only an insignificant number of investigations have been devoted to the study of the level along the height of the tree crown.

The branches of the tree are formed in different environmental conditions. At different ages and developmental stages of the organism's life, they are influenced in their state by their distance from the root, and by microclimatic conditions—temperature, moisture, light.

The attention of investigators has long been drawn to the question of selection and quality of grafted and rooted cuttings. It was noted [3, 13, 14] that large variation in the planted material often occurred from the fact that the location of shoots in the crown was not taken into account, and therefore cuttings of various ages and states were taken for grafting. The heterogeneity of the seed generation of each separately-taken specimen is also explained by the multi-level location of fruit-bearing organs [14]. A practical conclusion from these works is that different levels of the crown give qualitatively different planting and seeding material.

The basic problem of the investigations which we carried out is the study of the effect of the levels of the mentor's crown on the degree of transmission of characteristics to the hybrid seedlings developed.

METHODS

As mentors we took twenty-five to thirty-year-old frost resistant scion-rooted apple trees of I. S. Gorshkov's selection (seedlings No. 2 and No. 37) and of S. F. Chernenko's selection (seedlings No. 28-53 and No. 1) and also forty-five-year-old trees of Antonovka, Grushovka, and Anis.

Scions of the apple Anis aportovoi were grafted onto the first four seedlings mentioned above; on the latter three varieties were grafted Anis aportovoi (Anis as mentor) and seedlings of the combination Borovinka x Renet Simirenko (Antonovka and Grushovka as mentors).

A seedling of wild frost-resistant pear was taken as a mentor for a five-year-old seedling of a pear of southern origin. The scions of Anis aportovoi, Borovinka x Renet Simirenko and seedlings of the pear of southern origin were taken from the middle level of the crown and the middle part of the shoot. Scions were placed on the lower, middle and upper levels of the mentor's crown from the southern and southwestern sides.

TABLE 1
Sugars, Acidity, and Ascorbic Acid in the Fruits of Different Levels of the Crown of Apple Tree No. 2 and Its Grafts

Levels of
the crown
Apple tree No. 2 Anis aportovoi Apple tree
No. 2
Anis aportovoi Apple tree
No. 2
Anis aportovoi
Mentor Grafts Scion roots Mentor Grafts Scion
roots
Mentor Grafts Scion roots
Sugars (in per cent of wet weight)
Reducing Sucrose Sum Reducing Sucrose Sum Reducing Sucrose Sum Acidity in per cent of dry wt. Ascorbic acid in mg percent of dry weight
Lower 8.48 2.67 11.15 7.64 1.19 8.83 7.32 1.12 8.44 1.55 1.82 2.46 10.9 9.3 5.0
Middle 8.16 2.03 10.19 7.24 1.07 8.31 7.54 1.28 8.82 1.66 1.82 2.36 10.5 8.4 8.9
Upper 9.60 2.94 12.54 9.08 1.54 10.62 7.96 1.54 9.50 1.18 1.71 2.14 18.1 10.4 9.5

The work was begun in 1952 and was carried out in experimental plots of the I. V. Michurin Central Genetic Laboratory.

We have observed that opening of the bud scales and opening of the buds begins earlier on the root suckers and on the lower levels, both in the trees of mentors and in grafts. This difference is sometimes as much as 2-3 days. We noted the same in laboratory conditions on cut branches in the winter-spring. A significant difference was observed in flowering. The lower levels of the crown begin to bloom earlier. In 1955, in seedling No. 2 the scions of Anis aportovoi, grafted on the lower, upper, and middle levels of the crown of the seedlings were the first to bear fruit. The upper level of seedling No. 2 has accelerated the fruit ripening of Anis aportovoi grafts by one and one-half to two weeks. In the fruits of upper levels and their grafts we found a greater percentage of sugar, lower acidity, and a greater amount of ascorbic acid. It should be noted that the fruits were harvested at the same stage of ripeness. (Table 1).

This phenomenon we explain by the difference in illumination and temperature conditions in upper and lower levels of the crown, as well as peculiarities of metabolism and water regime connected with age and stage changes, as well as with the distance from the root.

Many life processes in the plant depend to a considerable degree upon the state of water metabolism, among them the ability of the organism to endure unfavorable environmental conditions such as drought, wintering, etc. [11, 15-17]. The investigations of Zalenskii [6] showed that an increase of the degree of xeromorphy of leaves in the shoot is reflected in the quantitative increase of various anatomical-morphological characteristics. Not only structural, but also physiological-biochemical characteristics, change as one moves from the lower levels of leaves to the upper ones [6-8, 18]. Sisakian [17] established that the higher the level of the leaf on the shoot, the greater is its ability to endure water lack. From the data of Eremeev [18], it follows that in the leaves of fruit trees a repetition of physiological and anatomical indicators (physiological parallelism) is observed in the limits of every shoot of the crown. The lower leaves of every shoot are less drought-resistant. Unfortunately, this author does not give in his paper comparative data on leaves of the same age in shoots taken from different parts of the crown. According to the data of Guseva [9], there is much more biological similarity between upper and lower branches of different trees (of the same age and variety) than between upper and lower branches of the same tree.

We established that the water exchange of the apple trees and pear trees takes place in a different way in various levels of the crown. There are changes in the transpiration rate, in the suction tension, osmotic pressure, the state of water in leaves of the lower level as compared with the upper, the rate of respiration, sugar content in leaves. The change in transpiration rate changes the usual rate of physiological processes. The transpiration rate was determined by weighing samples of leaves on a torsion balance. A large loss of water by the leaves of the mentors and grafts was noticed in the lower level (Table 2).

TABLE 2
Transpiration Rate of Grafts of Anis aportovoi and leaf of Southern Origin on Various Levels of the Seedlings of Apple and Pear

Name of
seedlings
and date of
analysis
Levels of
the crown
In mg per
g wet weight
of leaves,
average for
5 minutes
In g per m2
leaf surface,
average for
5 minutes
Name of
seedlings
and date of
analysis
Levels of
the crown
In mg per
g wet weight
of leaves,
average for
5 minutes
In g per m2
leaf surface,
average for
5 minutes
Apple tree
No. 2,
July 3
Lower 41.2 9.49 Forest pear,
Sept. 7
Root suckers 45.0 6.69
Middle 32.7 6.38 Lower 43.3 6.38
Upper 24.5 6.08 Middle 35.0 5.19
  Upper 28.3 5.63
Grafts of Anis
aportovoi
on apple tree
No. 2, July 6
  Grafts of
southern pear
on forest pear,
Sept. 7
Root suckers 42.3 6.31
Lower 45.3 7.27 Lower 64.0 9.49
Middle 43.4 5.05 Middle 50.6 7.43
Upper 38.2 6.67 Upper 35.0 5.93

Similar data were obtained with the other experimental objects. In 1955, we studied water loss by leaves from 7 A.M. to 5 P.M. It turned out that in the earlier period the leaves of upper levels transpired to a greater degree; in the hot part of the day, when the air becomes more dry, the upper leaves decrease their transpiration. On the average for ten hours, the greater water loss is found in the leaves of lower levels. In the hot hours of the day, the upper level leaves close their stomates, while in the lower leaves the stomates remain open.

The greatest transpiration rate was observed in the end phase of grand growth, then In the state of (lowering, and the least transpiration rate was observed in the period of termination of vegetative growth.

The grafts on the lower level transpired in the same way as the level on which they were grafted. For example, the transpiration rate over 5 minutes of apple tree No. 28-53 was 3.85 g/m2 In the lower level, 2.84 in the middle level and 2.14 in the upper level; the graft of Anis aportovoi on apple tree No. 28-63 in the same five minutes transpired 6.30 g/m2 at the lower level, 6.15 In the middle level, and 5.86 in the upper level.

As was shown by Maksimov [11], at normal atmospheric humidity the osmotic pressure of the cell sap may decrease the transpiration rate, which is confirmed by our data (Table 3).

TABLE 3
Transpiration Rate of Experimental and Control Leaves at Various Levels of the Crown in Apple and Pear Seedlings*
(Date of apple analysis, May 20, pear - May 19)

Experimental
treatments
Levels of
the crown
Transpiration rate Experimental
treatments
Levels of
the crown
Transpiration rate
mg per g wet
weight for
five minutes
g per m2 leaf
surface for
five minutes
mg per g wet
weight for
five minutes
g per m2 leaf
surface for
five minutes
Apple tree No. 25-53 Forest Pear
Control Lower 81.2 3.85 Control Root suckers 149.2 7.12
Middle 71.2 2.84 Middle 83.8 6.23
Upper 56.1 2.14 Upper 117.1 6.23
Stomates covered
by lanolin
Lower 18.9 0.92  
Middle 23.4 0.92
Upper 19.9 0.93
Cuticle coated
with lanolin
Lower 83.8 2.66 Stomates
covered
by lanolin
Root suckers 38.5 0.48
Middle 76.3 2.87 Middle 23.6 0.48
Upper 66.9 1.90 Upper 26.2 0.48

* Control leaves were not coated with lanolin; in experimental ones, either cuticle or stomates were covered by lanolin.

TABLE 4
Water Content in Leaves of Various Crown Levels of the Seedlings of Apple and Pear

Kind of seedlings Levels of
the crown
May 26-28 July 8-12
Total Free Bound Total Free Bound
Apple tree No.2 Upper 67.9 48.5 19.4 56.5 28.9 27.6
Middle 67.9 50.1 17.8 58.7 27.9 20.8
Lower 68.65 51.7 16.8 59.0 34 9 24.1
Apple tree No. 37 Upper 74.0 52.0 22.0 64.1 23.4 40.7
Middle 74.1 53.2 20.9 64.2 25.2 39.0
Lower 75.0 54.7 20.3 61.5 22.8 38.7
Forest pear Upper 65.4 19.5 46.2 52.2 36.2 16.0
Middle 66.3 10.8 55.5 54.7 44.0 10.7
Lower 66.4 30.2 36.2 55.1 47.5 7.6
Root suckers 73.5 35.9 37.5 60.1 54.5 7.6

However, osmotic pressure and stomate regulation alone are not sufficient to explain the higher transpiration of the leaves of the lower level as compared with the upper level. After coating the cuticle with lanolin, the transpiration rate was insignificantly changed. The leaves of the lower level transpired more rapidly than the leaves of the upper level, just as when the cuticle was not coated with lanolin. If the stomates are covered with lanolin, the transpiration rate sharply decreases, and the difference in the transpiration rate of leaves of various levels of the crown is decreased.

In our investigation, the actual age of the leaves is the same, but the leaves of the upper levels develop on branches which are older and are more mature, and therefore they have somewhat different properties than leaves on the lower levels. It is quite possible that the leaves of the lower levels, which have arisen at an earlier stage of tree development, having a greater free water content, use it more rapidly in the process of transpiration, which is continued by the data of Table 4.

TABLE 5
Osmotic Pressure and Suction Tension of the Leaves of Various Crown Levels in Seedlings of Apple and Grafts

Kind of seedlings Levels Osmotic
pressure
in atm.
Suction
tension,
atm.
Apple treeNo. 2 Lower 2.64 2.64
Middle 8.13 6.70
Upper 9.87 9.58
Apple  tree No. 37 (mentor) Lower 5.29  5.29
Middle 9.87 6.70
Upper 11.11 9.58
Grafts of Anis aportovoi
on apple tree No. 37
Lower 6.05 5.31
Middle 6.47 5.63
Upper 8.10 7.12

Within the stem, the water is distributed unevenly: its content (in percent) in most varieties increases from the base to the top. Within the crown, however, the moisture of the wood reaches a maximum in the lower part and decreases towards the top of the tree [20]. Out data on the determination of total, free, and bound water in leaves of the same age show that the greatest percentage of the total water present is contained in leaves of lower level, while the greatest percentage of bound water is found in leaves of upper levels. The same phenomenon was observed in one-year-old sections of branches at various levels (Table 4). in the winter period of 1954-1966, we studied the water content in buds and shoots. The data of these analyses showed that a greater percentage of water is contained in the branches and buds of the lower level than in branches and buds of the upper level. Thus, on February 17, in Renet bergamotnyi 48.3% water was found in the buds of the lower level and 43.3% in the buds of the upper level; in Pepin 4, 37% water was found in the buds of lower level and 34% the upper level; 40% in the shoots of the lower level and 36% in buds of those of the upper; in the shoots of the apple tree No. 37, 46% water was found in the upper level and 49% in the lower.

Evidently, the leaves of the upper levels are distinguished by greater resistence to water lack. According to Alekseev [15], the free water is most easily transpired from plants. Bound water is transpired with greater difficulty. It determines the stability of the protoplasmic colloids and the resistance of the organism to unfavorable environmental conditions, particularly drought. In this connection, osmotic pressure, suction tension, and the xeromorphism of leaves of various crown levels in seedlings and grafts were investigated.

TABLE 6
Sugar Content in Leaves of Various Crown Levels in Apple. Pear, and Their Grafts

Kinds of trees Levels of
the crown
May - June July - August
Reducing Sucrose Sum Mentor Grafts Own roots
Reducing Sucrose Sum Reducing Sucrose Sum Reducing Sucrose Sum
Apple tree No. 2
(mentor) and Anis
aportovoi (graft and
scion-root)
Upper 2.11 0.54 2.65 4.28 0.82 5.10 2.72 0.48 3.20 - - -
Middle - - - 3.76 0.94 4.70 - - - 2.06 0.82 -
Lower 1.47 0.48 1.95 3.70 0.65 4.35 2.44 0.44 2.88 - - 2.88
Forest pear (mentor)
and seedling No 2
(graft and scion-root)
Upper 3.29 1.03 4.32 2.85 0.64 3.49 3.06 0.71 3.77 - - -
Middle - - - 2.76 0.15 2.91 3.06 0.40 3.46 2.42 0.34 2.76
Lower 3.23 0.65 3.88 2.68 0.15 2.83 2.70 0.19 2.89 - - -
Antonovka (mentor)
and Borovinka x
Renet Simirenko
seedling (graft and
scion-root)
Upper - - - 3.17 0.27 3.44 3.14 0.75 3.86 - - -
Middle - - - 3.13 0.21 3.34 2.98 0.68 3.66 3.46 0.68 4.14
Lower - - - 2.84 0.08 2.92 2.93 0.59 3.52 - - -

Determination of osmotic pressure was carried out plasmolytically with sucrose. The leaf was always taken from the same level; therefore leaves were of similar age. The suction tension, too, was determined in these leaves by means of a refractometer (Table 5),

Osmotic pressure and suction tension of the leaves of upper crown levels in trees is higher than in leaves of the lower levels. Our data on osmotic pressure and suction tension of leaves from various levels correspond to the data of a number of other authors [15, 18, 20]. The leaves of the upper levels of the grafts and the leaves of the upper levels of the crown have a higher osmotic pressure as in our experiment with apple. The higher osmotic pressure and suction tension favor water movement into the upper levels of the tree crown.

As was noticed earlier, the lower transpiration of the upper level as compared with the lower level may also be explained by an increased osmotic pressure of the leaves of the upper level and by their smaller free water content.

We have found significant differences in sugar accumulation; there are more sugars in the leaves and shoots of the upper levels, which, evidently, explains the higher osmotic pressure of the cell sap in the leaves of these levels (Table 6).

The leaves of the upper level are distinguished by smaller epidermal cells, a more extensive vascular network, and smaller stomates, but by a greater number of stomates per unit of leaf surface. In Table 7, the comparative dimensions of stomates of the upper, middle, and lower levels of crowns and their grafts are given.

From the data of Table 7, it is seen that the mentor has an effect on the structure of the leaves of the graft. Leaves of the grafts on the upper level are formed under more severe conditions of water regime; as do the leaves of upper level of the mentor, they begin to show characteristics of xeromorphism: smaller epidermal cells and smaller stomates, and a greater number of stomates per unit of leaf surface.

Zalenskii [6] and Maksimov [11]. working with herbaceous plants, have noted that the upper leaves, in spite of their xeromorphic structure, possess a greater transpiration rate in spite of greater osmotic pressure. According to them, the increased transpiration of the upper leaf level favors a better water supply in the upper parts of the plant. We have not observed such a phenomenon in our experiments. The upper levels of the seedling crown, being in the more difficult conditions of water regime, use water more economically, and absorb it by the development of greater osmotic pressure and increased suction tension.

TABLE 7
Stomates Dimensions in Grafts on Various Crown Levels of Seedlings of Apple and Pear in mm (Ocular 15x, Objective 40)

Kind of seedlings Level of
the crown
Length of
stomates (1)
Width of
stomates (2)
Product
(1) x (2)
Apple tree No. 2 Lower 0.231 0.115 0.026
Upper 0.205 0.108 0.022
Grafts of Anis aportovi on
seedling of apple tree No. 2
Lower 0.241 0 129 0.031
Upper 0.209 0.107 0.022
Forest pear Lower 0.327 0.141 0.046
Upper 0.269 0.123 0.033
Grafts of southern pear on
forest pear
Lower 0.266 0.149 0.039
Upper 0.264 0.143 0.037

The more rapid respiration of leaves in the upper level evidently may favor better water absorption since it is known that, in addition to energy processes, respiration is also connected with growth processes. Respiration serves for supporting the protoplasmic structure in a viable state: it is necessary for absorption of mineral salts and water; it also regulates the process of fruit ripening etc.

We determined the rate of respiration (Table 8) by a gasometric method using a Warburg apparatus, and also by the method of Boysen-Jensen. The data obtained by the two methods are in complete correspondence.

TABLE 8
Respiration Rate of Leaves from Various Crown Levels in Apple Seedlings

Kinds of plants Levels of
the crown
Amount of oxygen absorbed
In mm3/g of wet
weight of leaves
In percent of
the upper level
June 21-22 July 22-28 June 21-22 July 22-28
Apple tree No. 37 Upper 307.6 236.0 100.0 100.0
Middle 301.0 175.3 97.8 74.2
Lower 256.4 130.0 83.3 55.0
Apple tree No.2 Upper 287.2 192.9 100.0 100.0
Middle 184.8 167.7 64.3 86.9
Lower 195.8 149.6 69.7 72.4

As can be seen from the data in Table 8, in June, when growth of branches is still observed in trees, the respiration rate is higher as compared with the end of July, when their growth is already terminated. The leaves of the upper level respire considerably more rapidly than do the leaves of the lower level. The same results were obtained with other experimental trees. Thus, for example, on July 28 the respiration rate of pear leaves in the upper level was 123.4 mm3 of oxygen per g of wet weight, and in the lower level - 72.5 mm3 of oxygen per g of wet weight of leaves.

For diagnosis of drought resistance and ability to withstand water lack we used the starch test-desiccator method, proposed by Genkel [21, 22]. The results of our analyses showed that the greatest amount of starch is found in the leaves of the upper level after they are held in a desiccator above sulfuric acid for 1.5 hours. The leaves of the upper level also have a greater capacity to endure water lack.

On the basis of these investigations, we conclude that the leaves and shoots of the upper levels of tree crowns are more adapted to the environmental conditions, and are more drought resistant.

SUMMARY

1. The morphological and physiological nature of various parts of the crown differ. This qualitative difference materially influences grafts. Water conditions in the leaves of top level grafts are more stringent and the grafts, just as the top levels of the mentor crown, form more xeromorphic leaves.

2. As compared to graminaceous plants the more xeromorphic organization of the top level leaves does not lead to an increase in the intensity of transpiration; on the contrary, a lower rate of transpiration is observed due to increase of the amount of bound water and enhancement of osmotic pressure.

3. The physiological nature of the leaves of the graft and the leaves of the level where the graft was inserted are very similar. Leaves of shoots of the top part of the crown are more drought resistant, and the transpiration rate in them is much smaller during the warmest hours of the day.

4. The top, middle and lower levels of the crowns of the mentors exert different influences on hybrid seedlings. This is due to differences in metabolism, water conditions and also to different conditions at various heights of the tree crown. One may suppose that more drought-resistant organisms will be developed in the upper levels of the crown.

Received January 16, 1956

LITERATURE CITED

  1. N. N. Glushchenko, Zhur. Obshch. Biol. 14, 2, 413 (1953).
  2. L M. Golubinskii, Agrobiologiia No. 1, 147 (1948).
  3. S. Kh. Duka, Iarovizatsiia, No. 4, 30 (1940).
  4. T. N. Bel'skaia, Methods of Investigation of Age Changes in Plants as Related to Morphological Characteristics* Izd. AN SSSR 1949.
  5. N. I. Dubrovitskaia, References to Papers in Establishment of Departments of Biological Sciences of Academy of Sciences USSR for 1944,* Izd. AN SSSR 1945.
  6. V. R. Zalenskii, Materials for Quantitative Anatomy of Various Leaves on the Same Plants, Izd. Kiev Politekhn. Inst. Vol. IV, 1 (1904).
  7. V. R. Zalenskii, lzv. Saratovskoi Opyt. S. Kh. Stantskii No. 1, IV (1918).
  8. V. O. Kazarian, Physiological Characteristics of the Development of Biennial Plants,* Erevan 1954.
  9. A. L. Kursanov and A. K. Briushkova, Biokhimia 5, 2, 521 (1940).
  10. S. D. Uvov and L. Kh. Berezniagovskaia, Eksperim. Bot. No. 1 (1934).
  11. N. A. Maksimov, Selected Works,* Vol. 1, Izd. AN SSSR 1952.
  12. I. V. Michurin, Works,* Vol. 1, Selkhozgiz 1948.
  13. V. P. Nilov, Collected Essays in Biochemistry and Physiology of Woody and Shrubby Southern Varieties.* lzd. VASKhNIL 1939.
  14. Iu. V. Porutskii, R. D. Alekseenko and M. A. Osetskii, Agrobiologiia No. 2, 80 (1949).
  15. A. M. Alekseev, Water Regime of Plants and Effect of Drought on it,* Tatgosizdat 1948.
  16. P. A. Genkel, Drought Resistance of Plants and Methods of Increasing It.* lzd. AN SSSR 1946.
  17. N. M. Sisakian, Biochemical Characteristics of Drought Resistance in Cultivated Plants,* lzd. AN SSSR 1940.
  18. G. N. Eremeev, Collected Essays in Biochemistry and Physiology of Woody and Shrubby Southern Varieties,* Izd. VASKhNIL, 1939.
  19. E. I. Guseva. Tr. Sochinskoi Plodovoi Zonalnoi Opytnoi Stantsii, No. 8 (1934).
  20. A. D. Poleshchuk, Doklady VASKhNIL, No. 23-24 (1940).
  21. P. A. Genkel, Doklady Akad. Nauk SSSR 86, 5, 1049 (1952).
  22. P. A. Genkel and K. P. Margolina, Doklady Akad. Nauk 86, 4, 849 (1952).

*In Russian.