Genetica (1965) 36, 301-306
THE METHOD OF POLLINATION WITH A POLLEN MIXTURE TO OBTAIN INTERSPECIFIC HYBRIDS OF PLUM AND CHERRY
KH. K. YENIKEYEV

Scientific Research Institute of Horticulture
Biryulyevo, Moscow, U.S.S.R.
(Received November 13, 1964)

The obtaining of blackthorn x plum hybrids is greatly facilitated by using a pollen mixture of different plum varieties (as compared with pollination by each plum variety separately). This also holds for the backcross to the plum, where the plum is the pollen parent. The cross sand cherry x plum only succeeded when plum pollen was mixed with myrobalan pollen. A number of triple interspecific hybrids has been obtained.

Introduction

A number of investigators have shown that if mixed pollen of different varieties, belonging to the same botanical species as the plants pollinated, falls on the stigma of apple, plum, gooseberry, or currant, the results appear to be considerably better than when pollination is carried out with the pollen of any single variety, even if it is a good pollinator. The first method gives better fruit and seed setting, and greater vigour and increased growth of the seedlings. Therefore, the possibility of mixed pollination should be taken into consideration in the design of commercial fruit-gardens and also of seed-gardens, where seeds are harvested for the production of seedlings. In such intraspecific crosses, a pollen mixture ensures a wide gametic selection and improves the genotypic constitution of the progeny.

In interspecific hybridization, breeders and botanists use pollen mixtures to facilitate crossing, and to study the degree of relationship between different species within certain botanical genera. Different variations of pollination with pollen mixtures are used in experiments, depending on the problems involved and on the biological characteristics of the plant.

MITSCHURIN found with plants, the ovaries of which had a large number of ovules (e.g. Malus Mill. and Pyrus L.), that the addition of a small quantity of related pollen to pollen of the other species, facilitated the production of distant hybrids. In this case the related pollen creates, in fertilizing the majority of ovules, favourable conditions in the pistil for the growth of other-species-pollen-tubes and the fertilization by it of some ovules. A similar phenomenon was observed in our experiments with stone fruit which possess one ovule per flower. We pollinated the American sand cherry (Cerasus besseyi Baily), with a mixture of pollen of C. besseyi, Prunus ussuriensis Kov. et Kost., Cerasus tomenosa Thunb., Cerasus vulgaris Mill., Armeniaca vulgaris Lam., and Prunus persica Sieb. et Zucc. An overwhelming majority of the plants obtained showed characteristics of Cerasus besseyi, and a few plants were hybrids Cerasus besseyi x C. tomentosa and C. besseyi x Prunus ussuriensis.

An important variant of this is that crossing of two species can also be facilitated by applying to the one species a pollen mixture of several varieties or subspecies of the other species. GORSHKOVA (1947) obtained hybrids by pollinating the Siberian apple (Malus baccata var. sibirica Maxim.) with a mixture of pollen of several West-European pear varieties (Pyrus communis L.). The interspecific hybrids possess a combination of the features of both parental species.

TOLMACHEV (1947) achieved success in interspecific hybridization by pollinating the Siberian black currant (Ribes nigrum ssp. sibiricum) with a pollen mixture from several gooseberry varieties (Grossularia reclinata Mill.).

SERGEYEVA (1962) noted an increased vigour of interspecific gooseberry hybrids obtained by pollinating Grossularia hirtella Mich. with varieties belonging to the species Grossularia reclinata Mill.

In our experiments on crossing the American sand cherry (Cerasus besseyi) with the apricot (Armeniaca vulgaris), pollen mixtures of several European, Caucasian, and Central-Asian apricot varieties were used. This was more successful than pollination of the sand cherry with the pollen of any single apricot variety.

Recent Experiments of the Author

Hybridization of the blackthorn (Prunus spinosa L.) with the domestic plum (P. domestica L.) was also facilitated by using a pollen mixture of several plum varieties (cf. also YENIKEYEV, 1960, 1962). It can be seen from Table I that the percentage fruit set resulting from pollination of the blackthorn with a pollen mixture of three plum varieties, was much higher than that obtained after pollination with each variety separately.

TABLE 1
RESULTS OF POLLINATION OF BLACKTHORN ('P. SPINOSA' L.) BY THREE DOMESTIC PLUM VARIETIES ('P. DOMESTICA' L.) SEPARATELY AND MIXED

Blackthorn pollinated by Number of
flowers pollinated
Seeds obtained Seedlings grown
No. % No. %
Jefferson 2946 10 0.3 3 0.1
Green Renclod* 1922 79 4.1 18 1.0
Ulense Renclod 1486 11 0.7 5 0.3
Pollen mixture of these three 1483 286 19.3 268 18.0
*Reine Claude = Greengage

In some cases, the number of fruits and seeds obtained from pollination with a pollen mixture did not exceed the number obtained by pollination with the best pollinator separately. Then, however, the seedlings from pollen mixtures were as a rule the more vigorous ones.

F1 plants resulting from the cross blackthorn (2n = 32) x plum (2n = 48) have as a rule 40 chromosomes and are often sterile, setting only a few fruits. We pollinated these F1 hybrids with the pollen of three domestic plum varieties, both as a mixture and separately. Such back-crossing yielded some quite fertile plants with a chromosome number ranging from 40 to 48. From these we selected several plants, which combine the good winter-hardiness of blackthorn with the large fruits and good palatability of the plum, and which are of interest for cultivation in the gardens of the Central Belt of the U.S.S.R. The figures given in Table 2 show that the pollen mixture contributed to the success of the above-mentioned back-crosses, as it produced more seedlings than the pollen of a single variety.

TABLE 2
RESULTS OF POLLINATION OF F1 (BLACKTHORN X PLUM) BY THREE DOMESTIC PLUM VARIETIES ('P. DOMESTICA' L.) SEPARATELY AND MIXED

F1 (Blackthorn x plum)
pollinated by
Number of
flowers pollinated
Seeds obtained Seedlings grown
No. % No. %
Green Renclod 1736 5 0.3 3 0.2
Ulense Renclod 1073 1 0.1 1 0.1
Kolkhoznyi Renclod 3748 17 0.5 3 0.1
Pollen mixture of these three 1762 20 1.1 11 0.6

We used one more variant of mixed pollination for interspecific hybridization: Sand cherry (Cerasus besseyi) was pollinated by three distant stone fruit species: myrobalan plum (Prunus cerasifera Ehrh.), blackthorn (P. spinosa L.) and domestic plum (P. domestica L.). The pollen of each of these species was used separately, in a mixture of any two components, and in a mixture of the three components. Separate pollination produced hybrids between sand cherry and myrobalan plum and between sand cherry and blackthorn, but yielded no results at all with domestic plum pollen. The results with the 4 pollen mixtures are given in Table 3. The myrobalan pollen had a marked advantage over the other components in the mixtures, as it produced a much higher number of hybrid seedlings than either blackthorn or domestic plum pollen. It is interesting to note that domestic plum pollen in mixture at least with myrobalan pollen) did produce sand cherry x dom. plum hybrids.

TABLE 3
RESULTS OF POLLINATION OF SAND CHERRY WITH POLLEN MIXTURES OF MYROBALAN PLUM, BLACKTHORN AND DOMESTIC PLUM

Pollen mixture Number of hybrids of type: Total
Sand cherry
x myr. plum
Sand cherry
x blackthorn
Sand cherry
x dom. plum
Myrobalan plum + blackthorn 71  8 - 79
Myrobalan plum + dom. plum 37 - 1 38
Blackthorn + dom. plum - 2 0 2
Myrobalan plum + blackthorn + dom. plum 2 63 1 66

Each of the species has its characteristic 2n chromosome number: sand cherry - 16, myrobalan - 16, blackthorn - 32, and domestic plum - 48. We counted the chromosomes in the roots of the hybrids (122 plants). All plants identified by their morphological characteristics as hybrids between sand cherry and myrobalan had 2n = 16, and the hybrids between sand cherry and blackthorn had 2n = 24. The hybrids between sand cherry and plum had the unexpected chromosome number 2n = 16, though on account of their morphological characteristics we had expected a different result. The hybrids of sand cherry and myrobalan grew well and are quite fertile. Being hybrids of two geographically distant species, their genotypic composition is disrupted, i.e. they are not stable, and can be crossed with other distant species: blackthorn and Ussurian plum (Prunus ussuriensis). It is of great interest to study the possibility of using hybrids of sand cherry and myrobalan as dwarf seedling stocks.

The F1 sand cherry x blackthorn, being triploid (2n = 24), has poor fertility. But as a result of pollination with pollen mixtures of domestic plum varieties, we managed to obtain 2 fertile plants. In the somatic cells of these plants, we found that one plant (No. 8-55) had 2n = 48, and the other one (No. 8-56) 2n = 32. No. 8-55 is characterized by its good fruit yield. Its fruits are larger (9.2 g) than those of the F1 sand cherry x blackthorn itself (1.2 g).

Conclusions

  1. Mixing the pollen of several varieties of a botanic species facilitates crossing, e.g. hybridization of blackthorn with domestic plum.
  2. Pollination of distant hybrids gives the possibility of obtaining complex hybrid plants possessing the properties of several species, e.g. F1 (sand cherry x myrobalan plum) x blackthorn or x Ussurian plum, and F1 (sand cherry x blackthorn) x domestic plum.
  3. With the aid of pollen mixtures it is possible to show selective differences between pollen of different species in the process of distant hybridization (pollination of sand cherry with a pollen mixture of myrobalan, blackthorn and plum).
  4. The use of pollen mixtures for interspecific crosses may contribute to the solution of practical breeding problems and of theoretical questions regarding the evolution of species.

REFERENCES

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