The black-fruited aronia, which is so widespread in cultivation in the USSR, is devoid of any reliably detectable variability, at the same time differing significantly from the wild, American black-fruited aronia. This may provide grounds for recognizing it as a distinct species, Aronia mitschurinii Skvortsov et Maitulina (Skvortsov, Maitulina 1982).

In this communication, we are attempting to clarify the time, place, and biological mechanism of cultivated aronia formation. For this purpose we have reconstructed to the best of our ability the history of its introduction in this country and also studied its flowering, fruiting, and chromosome number.

The first reference to the presence of black-fruited aronia in Russia is found in the catalog of plants published by the Kremenets Botanical Garden, now in Ternopil Oblast of West Ukraine, under the name of Mespilus melanocarpa (Besser 1816). In 1823, M. melanocarpa was already cultivated in the Kharkov University Botanical Garden, Ukraine (Index plantarum... 1823). In 1831 it was grown in the Kwitka[-Osnovyanenko] Park, Moskalyovka District, Kharkov (Catalogue des plantes ... 1831). A herbarium sample collected in 1825 on the Crimea Peninsula, the Black Sea Coast, Ukraine and labeled M. melanocarpa is preserved in the Moscow University Herbarium. Morphologically this sample is no different from North American plants.

At about the same time black-fruited aronia arrives to St. Petersburg and Moscow. M. melanocarpa was listed in 1824 catalog of plants grown in the St. Petersburg Botanic Garden (Index plantarum ... 1824) and the Emperor's Garden in Pavlovsk, a suburb of St. Petersburg (Weinmann 1824, as Pyrus melanocarpa Willd.). In 1825 the plant makes it to the Index seminum of the Moscow University Botanic Garden (Index seminum ... 1825).

The first brief description of the black-fruited aronia in Russian was published by F.B. Fischer in 1839. He noted that the plant could endure the northern climate and would beautify any nursery (1839, vol. 2: 181). Later on, E.L. Regel (1874), R.I. Schreder (1899), and E.L. Wolf (1915) also mentioned aronia's hardiness sufficient for it to exist in St. Petersburg and Moscow.

Early in the 20th century black-fruited aronia was introduced to the Caucasus. Seed originating from the Caucasus botanic gardens were listed in the 1909 exchange list of the St. Petersburg Botanic Garden (Delectus seminum ... 1909). However, it never became widespread in the Caucasus and apparently soon disappeared, as we never succeeded finding any later reference to its presence there.

Early 20th century was the time of the introduction of black-fruited aronia to Siberia. According to 1913 Delectus seminum of the St. Petersburg Botanic Garden, it was growing in Pavel S. Komissarov's garden in a suburb of Omsk. [¹] Pavel Savvich Komissarov, Michurin's contemporary, is considered the founder of the Siberian horticulture; his former garden is now one of the state reservations. See more at http://www.omskmap.ru/point/achair/person/72

Before the 20th century aronia was cultivated exclusively as an ornamental plant. In all descriptions authors would refer to ornamental qualities of its flowers and shiny black fruit. Any notes on the taste of the fruit are absent from descriptions up until the early 20th century. It was I.V. Michurin (Mitschurin) who first attempted growing black-fruited aronia as an edible plant in the 90's of the 19th century. In his nursery in Kozlov (now Michurinsk), he had a few bushes of black-fruited aronia originating from Germany (Michurin 1948a). Exactly what propagules were received by Michurin remains unknown. Some (Barabash 1960) believe it was seed; others (Protsenko 1971, Kalinina 1973) write about cuttings. It is also unknown whether the received material already constituted a new large-fruited form or if this form was somehow first developed by Michurin.

To our opinion, there is enough evidence to believe that the latter is true. In his notebook (1948b: 345), among other new cultivars, Michurin lists "a mountain-ash ... (omission) received through selection from three generations of an acclimated variety." There was a total of four species of introduced mountain-ashes in Michurin's garden: Sorbus aria, S. alpina, S. latifolia, and S. melanocarpa. Since he never recommended the first three species for cultivation, we have to conclude that the note spoke about a new form of black-fruited aronia. Additionally, in another place he wrote: " I have introduced a few improved kinds of fruiting plants, among which ... is the described black-fruited mountain-ash" (Michurin 1948a: 142).

It is important to add that within the Baltic States and St. Petersburg/Leningrad—the area essentially connected with Germany as far as propagule exchange—large-fruited aronia was first encountered only at the end of 1940's. We never succeeded finding any information about black-fruited aronia in the German literature of the time.

I.V. Michurin recommended to use the new cultivated plant for agricultural shelter plantings and then process the fruit crop for a variety of technical applications as well as "dessert preserves in those harsh-climate areas where there is lack of other fruit." From the start of the 20th century, black-fruited aronia makes its way to the list of trees and shrubs with edible fruit. For example, V.V. Pashkevich (1912) said aronia fruit was suitable for jams. However, the brevity of that note makes us think he might not know the plant very well; it is also remains unclear whether he meant the wild species or new large-fruited aronia.

All our attempts to interview veterans of introduction business and browsing through literature sources did not yield any information about propagation and spread of Michurin's aronia early in the 20th century. Even the staff of the Pomology Research Institute named after Michurin (in Michurinsk) could not provide any such information at our request. It appears that up until 1930's Michurin's aronia was not much promoted.

Documented history of its introduction starts only in 1935 [²], I.V. Michurin died in 1935. when Mikhail A. Lisavenko [³] 1897-1967, a renown Russian horticulturist, Director of Altai Horticultural Research Institute in Gorno-Altaisk/Barnaul (1932-1967) brought a few cuttings from Michurinsk to Gorno-Altaisk [⁴] The capital of Altai Republic within the Russian Federation, formerly known under names of Oirot-Tura and Ulala. These cuttings successfully overwintered outside, under the snow cover and became the source of extensive plantations of aronia in Siberia. In the 40's the Altai Research Institute (then called Experimental Station) started sending out seed and seedlings of Michurin's black-fruited aronia out to many different destinations within this country. In 1940, 10 seedlings from the Altai Experimental Station were planted in Vilgort, Komi Autonomous Republic. The seedlings proved to be hardy there and started to fruit after 4 years (Charochkin 1954).

In 1947 aronia from Gorno-Altaisk was introduced to Kaluga Oblast, central European Russia, near Moscow (Myatkovsky, Telyukov 1966), and in 1958 a first commercial plantation was started there in Bukhlovka State Farm. By 1969, there were 568 hectares (1,420 acres) of plantations around Kaluga (Myatkovsky 1970).

Also in 1947 the Gorno-Altaisk Experimental Station forwarded a load of aronia seedlings to Lesnoye [Forest] State Farm in Leningrad Oblast (Vasilchenko, Protsenko 1967). This institution became a source of aronia for the European Northwest of the USSR. Large shipments of seedlings were sent from there to Latvia, Lithuania, and Belorussia, as well as Kalinin (or Tver) Oblast and Vladimir Oblast (Shchukina 1967).

In 1948 cuttings of Michurin's aronia were forwarded from Leningrad to Kandalaksha [⁵] A town near the City of Murmansk, beyond the Polar Circle, at 67° N, on the White Sea (or Beloye More) Coast and first kept in a greenhouse there. Two-year-old cuttings of the second greenhouse generation were planted out near Apatity Railroad Station in 1954. They started fruiting in 6 years. According to B.V. Kester (1970), aronia of the Leningrad origin overwinters in Apatity with live terminal buds, flowers yearly, though fruiting occurs only during favorable years, and only 20-30% of fruit mature to ripeness.

With the material from Lesnoye, Leningrad, new plantations of aronia were stated in Zelenogorsk (Leningrad Oblast) in 1954 (Ignatenko 1965). In 1958 aronia from Lesnoye was also introduced to Kharyus in Estonia, and by 1965 the plant was cultivated in four different state farms in Estonia (Kask 1971). The population in Petrozavodsk, Karelia, northwestern Russia also originates from Lesnoye State Farm in Leningrad (Izergina 1969, 1971).

At the same time the area under the Siberian plantations continued to grow. A new plantation in Bakchar Branch of Tomsk Agricultural Experimental Station was started in 1957 (Gidzyuk 1966). Yet another one was developed in Tavricheskiy [Taurida] Fruit Farm in Omsk Oblast in 1964 (Ryzhkov 1973).

The Gorno-Altaisk Horticultural Experimental Station remained the major source of the introduction material. In 1958 seedlings from the Station were introduced to Aurgaz and Gafura Districts in Bashkiria [⁶] Now Bashkortostan, a republic within the Russian Federation situated in the southern Urals Mts. and south of the Urals (Barabash 1960; Suslov 1969). In 1959 the Altai Station forwarded the first shipment of Michurin's aronia seedlings to nurseries and teaching/experimental gardens of Udmurtia [⁷]. A republic within the Russian Federation in the western part of the Central Urals Soon it became one of the most widespread cultivated fruiting shrubs here. According to M.G. Kontsevoy (1974, 1975), as of 1970, there were three state farms in Udmurtia with plantations of aronia covering 40 hectares (100 acres) in each; and the total area in Udmurtia was 221 hectares (552 acres). In 1959 fist seedlings of aronia were planted in Kirov (or Vyatka) Oblast. The seedlings successfully took, became acclimated, and in four years the first commercial plantation was already underway. By 1974, the area under aronia in Kirov Oblast was 500 hectares (1,250 acres) (Cheglakov and others, 1974).

It is not known when Michurin's aronia was introduced to Ukraine. There is a brief note in Musich & Alexeyenko (1978) about aronia there before World War II, though there is no exact dates or sources mentioned. Indeed it is not even known whether that was Michurin's aronia or its wild ancestor, which, as we have said here before, had been grown in Kharkov and Kremenets as early as the beginning of the 19th century.

On the Island of Sakhalin (in the Russian Far East), in the State Farms Yablochnyy and Pyatirechenskiy [Apple Orchard Farm and Five-River Farm], there grows aronia originating from Altai and also from Leningrad material (Voronova 1967, Shchukina 1967).

Taking all of this information into account, we may state with confidence that all of cultivated aronia in this country originates from Michurin's nursery. The area of cultivated aronia covers a significant part of the USSR (Fig. 1), with a tendency for further expansion. For example, it has been being introduced in Moldavia and Belorussia's (Bibikov, Kramnik 1974; Zhungietu 1975), in the Baltic States, and Northern Caucasus (Myatkovsky 1970). Michurin's aronia is also successfully cultivated in private gardens and teaching/experimental stations in Arkhangelsk Oblast (about 64° N), coming there from Petrozavodsk and Vologda; in Volgograd Obl. (starting from 1963; introduced from Kuibyshev (or Samara)); in Astrakhan Obl. (about 46° N, at the mouth of the Volga River flowing into the Caspian Sea) (introduced in 1970 directly from Michurinsk).

In order to reveal causes of low variability of the cultivated aronia, we conducted experiments in June 1978, which included isolation, castration, and artificial pollination of flowers. The experiments were conducted in the Central Botanical Garden USSR Acad. Sci. using 5-year-old cultivated plants. At the stage of flower buds, the inflorescences were isolated with 3-layer mesh or oil-paper bags. There were 12 isolated inflorescences in each of the following 7 lots in the experiment:

1. Castrate flowers and remove stigmas
2. Castrate flowers without removing stigmas
3. Castrate flowers and pollinate with Chaenomeles japonica pollen
4. Castrate flowers and pollinate with pollen taken from the same flower
5. Castrate flowers and pollinate with pollen from the same inflorescence
6. Castrate flowers and pollinate with pollen from the same specimen
7. Castrate flowers and pollinate with pollen from the same population

Two different control lots were isolated intact flowers and flowers subject to open cross-pollination.

Such experiments conducted earlier had arrived to controversial results. For example, Bibikov & Kramnik (1974) did not obtain any fruit upon pollinating castrated flowers with alien pollen; at the same time, Kuzmina (1975) reported fruit formation upon pollination with alien pollen and upon treating stigmas with various stimulators.

In 1978 aronia started to flower on May 29, finishing on June 21, with a peak of flowering during June 4-10. There were on average 26 flowers per inflorescence. Flowering of a single inflorescence continued 10-13 days (4-5 days for each flower).

Bibikov & Kramnik (1974) observed some specimens with double flowers in aronia populations. In our plantings we did not have any specimens whose all flowers were double. When found (in 3 cases total), some double flowers were present within inflorescences with normal flowers.

Lot 1 (castrate flowers , remove stigmas) yielded only 6% fruit formation.

Lot 2 (castrate flowers, intact stigmas) yielded 58%.

Lot 3 (castrate flowers, pollination with Chaenomeles japonica) yielded 70%.

Lots 4, 5, 6 yielded 95-99%. [⁸]. Result for Lot 7 is not mentioned.

Control Lot 1 (isolated intact flowers) produced 68 % fruit.

Control Lot 2 (free pollination) yielded 79%.

These results demonstrate that aronia is capable of autonomous, spontaneous apomixis; however, with participation of pollen (either own or alien), fruit formation becomes more abundant. Taking into account the lack of variability in the progeny, we have to conclude that there is no real amphimixis in our aronia.

On the contrary, in A. melanocarpa within its natural range (North Carolina), similar experiments (isolation, castration, and artificial pollination) did not yield any evidence of apomixis (Hardin 1973). Moreover, in the northern part of its natural area (Nova Scotia), A. melanocarpa was found not to set any fruit even when self-pollinated, that is, behaving as a species with cross-pollination (Hall et al.1978). At the same time, A. arbutifolia is known to be apomictic (Hardin 1973); apomixis is also rather common in Sorbus. Therefore, apomictic character of Michurin's aronia is not something completely unexpected.

All literature sources (Moffett 1931, Sax 1931, Hall et al. 1978) report 2n=34 for A. melanocarpa as well as A. arbutifolia and A. x prunifolia. Moffett (1931) detected 2n=68 in A. arbutifolia cultivated in Kew Gardens.

We counted chromosomes in cultivated aronia originating from Moscow, Riga, Barnaul, and Sakhalin.

The following method was employed. Seeds packed in tissue bags, 40 g each, were soaked in water at room temperature for 24 hrs. Then the seeds in bags were stratified in damp peat moss (to prevent desiccation) for 4 months at 0 to +1°C. Stratified seeds were placed in Petri dishes on moist filter paper at room temperature for germination. In order to accumulate metaphase plates and obtain good chromosome spread in cells, roots 1-1.5 cm long were placed in 0.5% colchicine solution at 3-5°C for 24 hrs. and upon that fixated in Karnua solution for another 24 hrs. The material was washed twice in 80% alcohol and then preserved in 60% alcohol until the start of the count. Roots were stained in 5% acetocarmin, while the solution was heated to boiling for 5-8 min. In order to remove excess stain, roots were then kept for 10 min. in 45% acetic acid. Chromosome counts were made on temporary slide mounts, photographed with Amplival Microscope equipped with mf-matic device for microphotography.

All metaphase plates demonstrated 2n=68 (Fig. 2), which showed that Michurin's aronia cultivated in the USSR is an apomictic tetraploid race.

It is a known fact that both polyploidy and apomixis can either be induced by various factors or be of purely genetic nature. It is also known that polyploidy often results in apomixis. Michurin practiced crossings widely, including those of very remotely related species or those completed with pollen mix originating from a few species. Alien pollen could act as a stimulant triggering a transformation to polyploidy and apomixis. This scenario seems quite probable—especially if we consider prevalence of polyploidy and apomixis in the subfamily Pomoideae.

Yet polyploidy may result only in some (insignificant or even negligible) changes in size of plant organs, whereas the difference between the cultivated tetraploid aronia and its wild diploid ancestor is mostly qualitative (Skvortsov, Maitulina 1982). Therefore, it would be reasonable to assume that, in addition to changes in ploidy, some more important genome changes took place during the formation of the cultivated aronia. This could be, for example, a replacement of a chromosome(s) within a homologous pair(s) as a result of interspecific crossings with subsequent recombination during a hybrid split (let's remember that Michurin mentioned "selection within three generations"). Translocations could also take place, either with connection to hybridization or not. Any heterozygosity could have become permanent due to apomyxis.

Examples from another genus, Oenothera (Onagraceae), demonstrate that rather significant and permanent morpho-physiological changes in plants that are based on structural genome changes can emerge quite rapidly. Introduced from North America to Europe at the late 16th — early 17th century, representatives of this genus gave rise to new species unknown in North America, such as O. erythrocepala Borb. and O. rubicaulis Klebahn. It is difficult to interpret the new species formation as a result of hybridization with the European species, because these plants don't exhibit any characters that appear to be inherited from a European parent or intermediate between European and American plants.

Apparently, both in the case of Oenothera and Aronia, the new species formation has been triggered by drastic environmental changes, once plants found themselves on a different continent. However, mechanisms of the hereditary fixation of the changes have been different. There is no apomixis in Oenothera; instead there is a particular genus-specific cytogenetic mechanism that provides for the constancy of characters.

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Translation I. Kadis
30 December 2011