Cultivated blueberries

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Cultivated blueberries in sales trays
Cross section through cultivated blueberries
Typical autumn colors of the blueberry bushes
Jug-shaped flowers of cultivated blueberries

The blueberries are large varieties by breeding of plant species of the subgenus or section Cyanococcus in the kind of the blueberries ( Vaccinium emerged). Blueberries belong to the heather family of plants (Ericaceae). Cultivated blueberries do not originate, as is often assumed, from the blueberry, blueberry or wild blueberry ( Vaccinium myrtillus ) native to Europe , the fruits of which turn the mouth and lips blue when consumed, but are of North American origin. The coloring anthocyanins are found in the fruit skin of the almost spherical, blue berries; their flesh is white.

Over 100 new varieties have been cultivated since the beginning of the 20th century. Cultivated blueberries are important worldwide as market crops . Before it was cultivated as a fruit supplier , the cultivated blueberry had already been introduced as an ornamental plant in European gardening and landscaping because of its decorative autumn color .

Botanical description

Bark of older shoots
Top of sheet
Leaf underside
Sliced ​​berry with light brown seeds; the cells are destroyed by freezing. This is why the anthocyanins in the peel ran into the pulp when it was thawed.
Different berry sizes of feral forms

Cultivated blueberries are perennial , upright, multi-branched, deciduous subshrubs (Chamaephytes). They can grow to heights of up to several meters or grow as ground cover with only a few centimeters. Characteristic are jug-shaped flowers and blue, frosted berries.

Growth forms and root system

The shape (habitus) of cultivated blueberries varies from variety to variety. While some Auslese strive to be strictly upright, others grow wider and form an expansive shape. The group of tall bushy forms ( Northern and Southern Highbush Blueberries ) form 2 to 5 meters high, round, dense and compact bushes. The upright varieties of rabbit- eyed blueberries ( Rabbiteye Blueberries ) reach about 4 meters, half-high forms ( Half-Highbush Blueberries ) between 1 and 2 meters. The low- bush varieties ( Lowbush Blueberries ) are between 0.2 and 0.7 meters tall and form runners. They grow looser than the high-bush and semi-high-bush forms. The main plant mass consists of rhizomes from which the upright shoots grow.

The root system is highly branched and spread out close to the surface. It has a high proportion of fine roots, some of which are matted. They are fibrous and very thin, and unlike other plants, they are not endowed with root hairs , which are important for the absorption of water and nutrients .

Leaves and shoots

The wood of the shoots is hard and brittle, the bark is gray and cracked. Depending on the variety, they branch out more or less strongly. Young shoots are usually bare, green to yellowish green and partly reddish overrun (two-year-old shoots) with a warty surface.

The leaves are alternate on the shoot. They are fresh to dark green and bare on top. They are lighter in color underneath and, at least on the veins , usually slightly hairy. Around mid-June the shrubs developed their largest leaf area in the course of the year. Before the leaves are shed in autumn, the leaves turn yellow to bright red due to the formation of anthocyanins. This gives the cultivated blueberries a high ornamental value. The leaves of the tall to half-height varieties are ovate to elongated oval, pointed with smooth leaf margins. The leaf size is very different on the bush. The leaves of the side shoots are usually no longer than 5 to 6 centimeters, while those of the strong ground shoots reach 10 centimeters and more. The leaves of the low-bush selections are smaller than those mentioned above and usually more or less serrated on the edge.

Flowers, fruits and seeds

The yellowish white to pale pink flowers are shaped like a jar. This up to 20 millimeters long and somewhat inflated flower tubes consist of five grown together Blütenkronblättern . Each flower has eight to ten stamens at the base of the calyx , which in turn surround a significantly longer stigma . The nectar producing nectar are at the bottom of the calyx . The flower bud produces a clusters of up to twelve individual flowers. The lower flowers are stalked longer than the upper ones. Some varieties develop several corymbs from one flower bud. The flower buds appear mostly at the shoot tips, less at the shoot base. They are significantly rounder and stronger than the small and pointed leaf buds. Cultivated blueberries predominantly bloom on the side shoots of the first order. The ovary below is surrounded by five green sepals, which are recognizable as fleshy cusps on the ripe fruit.

All cultivated blueberry varieties have the light blue, bright blue to black-blue fruit peel of the berries in common. The pulp is whitish. The berries have a white frost on the surface, this coating is caused by microscopic wax particles that are formed in the fruit peel, transported to the outside with the respiratory water and deposited there. The size of the berries varies widely depending on the variety, they are on average between 5 and 12 millimeters wide, sometimes up to 30 millimeters.

The fruits contain 30 to 80, very small, light brown seeds. Around 4000 of the seeds weigh 1 gram. They are already capable of germination when the fruit is ripe and do not require a long cold phase ( vernalization ). The radicle appears after about 14 to 35 days, the cotyledons after about 3 to 8 weeks.

Growth and development

Chronological course of the development of cultivated blueberry bushes in Central Europe

Vegetative growth, flowering and fruit development in Central Europe extend over a period from around the beginning of April to mid-October. The harvest is from the beginning of July to mid-August. Due to the large spatial expansion of the North American blueberry cultures over different climatic zones , the harvest there begins as early as April in Florida and ends in Newfoundland at the end of September .

Vegetative growth

The main growing season of the shoots is between mid-May and early October. The annual growth of the shrubs and thus the yield decreases with increasing age, since the flowers are mainly formed at the tips of annual shoots. The flower and fruit set is at the expense of the shoot growth, so they become increasingly weak and thinner with increasing age; the bushes " grow old ". The shoots have a variety-specific production time. In the case of highly bushy forms, they produce flowers and fruits for four years and the yield is good. The selections of the rabbit-eyed blueberries bear seven years; in the low-bush forms, the new saplings that grow out of the rhizome do not bloom and produce fruit until the second year. Although the older shoots still produce fruits, these are usually smaller and the harvest remains low. In blueberry cultivation, regular pruning is therefore one of the most important care measures. This promotes vegetative growth and stimulates the formation of new shoots from the shrub base. The fruit size and quality are increased and fruit ripening accelerated. The removed wood, excess shoots and inward-growing branches are removed.

Root growth is strongest between 14 and 18 ° C soil temperature, and below 8 ° C it is clearly limited. Two phases of intense root growth occur in cultivated blueberries. Under Central European climatic conditions, these are around mid-May to early June and from mid-August to mid-September. Since the root system is not particularly effective at absorbing water, the shrub stops growing when the soil begins to dry out.

Flowering and fruit development

In Central Europe, the flowers are created in the previous year after fruit ripening between July and September ( flower induction ). In autumn the flower buds grow and differentiate so that they are almost completely developed in winter. The main flowering of cultivated blueberries is under Central European climatic conditions mostly in the first two weeks of May and thus later than in the North American growing areas. The flowering period extends over about four weeks, depending on the weather . The flowers of the shoot tips are the first to open, and within an inflorescence the upper and then the flowers closer to the ground always bloom first.

Most blueberries are self-fertilizing . Through targeted cross- pollination , a larger fruit set with larger fruits and shorter ripening times can be achieved in cultivated forms. The southern high-bush blueberries are only partially self-fertile and therefore also dependent on cross-pollination. The rabbit-eyed blueberry group and the low-bush varieties are predominantly self-incompatible . They are pollinated exclusively by insects. Play bumblebees ( Bombus ) and wild bees a decisive role. Pollination by honey bees ( Apis mellifera ) does not appear to be very effective as they tend to open the flowers from the side and do not ingest any pollen . The promotion of certain native plants on the cultivated areas plays an important role in the settlement and establishment of flower-visiting insects.

Fruit growth and ripeness extend over eight to 16 weeks, depending on the variety and weather. The fruits go through three phases of development. After fertilization, the young fruits rapidly increase in size for about four weeks through cell division in the fruit tissue. This phase is replaced by an apparent resting phase in which the fruits do not continue to grow, but the seeds or embryos store reserve substances inside . The fruit then increases in size again, although the number of cells no longer increases, but they absorb more water and stretch. At the end of this phase, the color of the fruit skin changes from green to pale green and purple to the typical blue, the fruit ripens and becomes soft. At the same time, the ingredients change: Sugar is built up (or stored) and acids are broken down. The characteristic aromas and the typical ripening of the surface are only formed at the end of the fruit ripeness. The latter fulfills several functions for the fruit: it protects the berry from excessive heating due to the reflection of the sun's rays; it prevents the penetration of microbial pathogens, after all rainwater rolls off completely, so that the berries dry quickly and harmful fungi do not have good development conditions. The fruits of a shrub do not all ripen at the same time, even within a fruit cluster. The stages of maturity are divided into six phases according to an American scheme, which are derived from the external color impression:

Ripe stages in an infructescence: R = ripe, IG = immature green, GP = green pink, BP = blue pink
Stage of maturity (English) German Fruit condition
IG = Immature Green Immature green Completely green and tough
MG = Mature Green Ripe green Light green to whitish, softer
GP = Green Pink Green pink Pink color of the calyx region
BP = Blue Pink Blue pink Beginning blue, stem region pink
B = Blue blue Blue, except for a pink ring in the region of the stem
R = Ripe Ripe Completely blue and frosted, soft

The seeds that are ready to germinate when the fruit is ripe germinate by 50 to 80%. It takes about six to ten weeks for the first leaf to develop. As soon as the tenth to fifteenth leaves appear, the first side shoots form, they quickly overgrow the main shoot and ensure early branching.

Resting phase

The winter rest phase ( dormancy ) is initiated by the decreasing day length and falling temperatures. In autumn, reserve materials (carbohydrates, starch, minerals) and the plant hormone abscisic acid are stored in the buds . The latter is intended to prevent the plants from sprouting too early in the unfavorable season, which could lead to frost damage. This inhibitor is broken down during the winter months, particularly effectively at temperatures between 0 and 7 ° C. In spring, indolylacetic acid , a growth-promoting hormone, increases. The cold demands of cultivated blueberry varieties are expressed in hours and are between 250 and 1200 hours. For low-growing varieties, the need for cold is over 1000 hours, for northern high bush varieties 800 to 1100 hours, for rabbit-eyed blueberries between 350 and 800 hours. The southern high-bush blueberries, which are common in warmer regions, have the shortest need for cold at 250 to 500 hours. In accordance with the need for cold, the plants have a "need for warmth", a certain amount of heat that ultimately leads the trees to sprout again in spring.

The natural internal growth rhythm of the woody plants would be disturbed in climatically unfavorable locations. In the southern regions of the USA, only those varieties are grown that have the lowest possible need for cold. Without a sufficient resting phase, the spring sprouting of the Lowbush varieties, for example, would be delayed and irregular. On the other hand, readouts with a low need for cold are not suitable for higher latitudes, as they sprout too quickly and too early and are therefore very vulnerable to frost.

Origin and Taxonomy

Vaccinium corymbosum , the fleshy, thickened remains of the sepals at the tip of the fruit

Cultivated blueberries are the result of breeding from the plant species of the genus Vaccinium native to the USA and Canada in the section or subspecies Cyanococcus or their hybrids . The exact number of species within the genus Vaccinium includes around 100 to over 400 species, according to different literature and taxonomic studies.

Over 100 new cultivated blueberry varieties have been cultivated since the beginning of the 20th century, and new ones are added every year. The older ones are selected from the naturally occurring wild stocks in North America (wild varieties). The majority of the current varieties, on the other hand, are targeted crossbreeding products. In addition to selections from the cross between V. angustifolium and V. corymbosum , cultivated forms of the parent species themselves, further hybrids from the American bilberry ( V. corymbosum ) and other species of the genus Vaccinium are in culture. The species Vaccinium pallidum , V. angustifolium (syn. V. lamarkii ), V. darrowi , V. elliottii , V. virgatum (syn. V. ashei ), V. caesariense , V. fuscatum also belong to the so-called northern hybrid complex (syn. V. atrococcum ), V. simultatum and V. myrtilloides .

The Vaccinium species that are grown as cultivated blueberries are listed in the following table. Polyploid cultivars are of particular interest for cultivation , as they can grow to be several meters high and thus significantly increase the yield per area and plant. The subdivision of cultivated blueberries is essentially based on the height of the bushes and their preferred growing regions. The species names follow the Germplasm Resources Information Network (GRIN). Some of them differ from those given in the main literature. The synonyms are given in brackets.

group English name Systematic designation / wild forms involved Degree of ploidy Origin / cultivation Brief description
High bush blueberries Northern Highbush Blueberries Vaccinium corymbosum L. Tetraploid Northeast USA, southern Canada Shrub height up to 5 m; strong, upright single shrubs; leaves with entire margins up to 8 cm long; Fruits blue, frosted, 0.7 to 1 cm in size, pulp colorless; Need for cold 800 to 1100 hours, frost hardness −25 to −35 ° C
Rabbit-eyed blueberries Rabbiteye Blueberries Vaccinium virgatum Ait. (syn. V. ashei Reade) Hexaploid Southeast United States Shrub height up to 4 m, strong, upright individual shrubs; small, entire leaves; heat and drought resistant; short hibernation; Fruits black with large seeds; the calyx region of the fruit is reminiscent of the eye of a rabbit, hence the name; Need for cold 350 to 800 hours, frost hardness −20 to −25 ° C
Southern high bush blueberries Southern highbush blueberries V. corymbosum L. hybrid with V. darrowi Camp. or V. virgatum Ait. (syn. V. ashei Reade) and V. formosum Andrews (syn. V. australe Small) and other Vaccinium species Tetraploid Southeast states of the USA along the Atlantic coast Bush height 2 to 4 m; many root shoots; forming dense colonies; large leaves (2.5 to 8 cm); Fruits blue, over 1 cm in size; Cold need 250 to 500 hours, frost hardness −15 to −20 ° C
Half-high blueberries Half-highbush blueberries Vaccinium corymbosum × V. angustifolium (syn. V. lamarkii ) = V. × atlanticum Bickn. Diploid, tetraploid Northern states of the USA, Canada Bush height 1 to 2 m; Leaves 3 to 8 cm; Fruits bluish black, frosted, whitish inside; the specimens show a great variability in the characteristics of the parent species; very cold tolerant
Low growing blueberries Lowbush blueberries Vaccinium angustifolium Ait. (syn. V. lamarkii ), V. myrtilloides Michx. Diploid, tetraploid Northeast USA, Canada Bush height 0.2-0.7 m; Leaves 2 to 4 cm, small and serrated, hairy in V. myrtilloides ; partly dense stands, forming runners; Fruits black-blue, blue, metallic blue frosted, up to 0.7 cm; Cold requirement> 1000 hours, frost hardness −25 to −40 ° C

History of cultivation

Vaccinium darrowii
Vaccinium angustifolium

As far back as the last decades of the 19th century, North American farmers were growing the first wild forms of blueberries in their home gardens, mostly without great success, because the berries remained very different in size, shape and taste. They came to the conclusion that “blueberries” could not be cultivated for the market. It was not until the turn of the century that the plant breeder Elizabeth Coleman White (1871–1954) initiated a program to select suitable blueberry bushes. In 1911 she made contact with the botanist Frederick V. Coville (1867-1937), who had been carrying out selection attempts from wild stocks since 1906, and a cooperation was established. While the Whites family had the financial means and a farm in the Pine Barrens with the necessary infrastructure for an extensive selection program, Coville provided the scientific background knowledge. White's father, JJ White, a successful farmer, engineer and investor , marketed cranberries ( Vaccinium macrocarpon ) as well as blueberries from wild stocks in the surrounding moors and swamps, which were picked by seasonal workers. As part of the selection program, the pickers were commissioned for a fee to locate the best bushes with the largest and sweetest fruits in the area; Elizabeth White named the bushes after their finders. The plants were divided and first planted under glass on the Whites farm. After just five years, White and Coville had created a high-yielding, large-fruited variety in 1916 that was ready for marketing. The "first cultivated blueberry" was named 'Rubel' after Rube Leek, who found the bush. It was a shrub of Vaccinium formosum from which the wild variety was selected. It is still grown today and is part of a number of breeds and numerous subsequent selections.

The blueberry acreage grew rapidly, especially in the eastern United States. In the 1950s, the total area under cultivation in the USA was around 8,000 hectares; in the 1990s, cultivated blueberries were grown in 36 US states on an area of ​​20,000 hectares.

Share of blueberry types in North American cultivation including Canada in 2000:

group Area (ha) Proportion of (%)
Northern Highbush and Half-Highbush 20,830 24.6
Rabbiteye 5,220 6.3
Southern highbush 1,840 2.3
Wild populations 56,600 66.8
total 84,490 100

In Europe, the first cultivated blueberries for the purpose of berry production were planted in the Netherlands in 1923. Blueberry cultivation began in Germany in 1930 under the direction of the botanist Wilhelm Heermann . The first large cultivated blueberry fields were created in 1950. The main growing areas in Germany are in the Lüneburg Heath , in Brandenburg, in the Oldenburg area as well as in southern Germany and central Baden. Essentially, tall to half-height forms are used. Lower forms are becoming increasingly important because of their more aromatic fruits. In addition to the USA and Canada, there is significant cultivation in Chile, Argentina, New Zealand and Australia. In Europe, blueberries are grown in Germany, Poland, the Netherlands, France and Spain. While the cultivation area here still comprised around 2300 ha in 2003, it had almost doubled to around 4500 ha by 2006.

State of international breeding

The focus of the cultivation of cultivated blueberries is in the USA. After the efforts of the pioneers in the 1950s and 1960s, German varieties largely came to a standstill today. Since around the end of the 1980s, cultivated blueberries have been increasingly processed in New Zealand and Australia. Today genetic engineering methods are used to shorten the lengthy breeding process and to be able to cross the desired properties in a more targeted manner. Criteria for the fruit quality are the fruit size, the fruit color, the content of anthocyanins, the firmness, the space resistance, a long shelf life and the aroma. The selections also focus on increasing the organic cultivation width, tolerance to higher pH values ​​in the soil, high tolerance to drought, resistance to diseases and pests, as well as late flowering and earlier harvest.

The North Carolina State University (USA), Michigan State University (USA), the Nova Scotia Wild Blueberry Institute (Canada), the Horticultural and Food Research Institute of New Zealand and the Australian Institute of are working particularly hard to improve cultivated blueberries Horticulture worked.

Cultivated blueberry varieties

The variety 'Polaris'

The German breeder Wilhelm Heermann selected the 'blue-white gold grape' and the 'blue-white sugar grape' from the hybrid Vaccinium corumbosum × V. angustifolium , from which later the varieties 'blue-white gold grape 71' and 'record' were read out. Furthermore, 'Herma I' and 'Herma II', 'Gila' and 'Greta' come from Germany. The varieties mentioned are still grown today. Most of the varieties come from the USA, there are also crosses such as 'Bluerose' and 'Maru' and 'Rahi' from Australia and New Zealand.

Around 20 to 30 cultivated blueberry varieties have established themselves worldwide and are being cultivated on a larger scale, the world market leader is the 'Bluecrop' variety. Above all, its ability to deliver high and regular yields at very different locations was the basis of its global triumph, moreover it is cold-hardy, drought-tolerant and less susceptible to diseases and pests.

A selection of varieties (Northern Highbush and Rabbiteye group), their origin, year of introduction and descent are given in the following table:

variety Country, year of introduction ancestry
'Berkeley' USA, 1949 'Stanley' × ('Jersey' × 'Pioneers')
'Blue and white gold grape 23' Germany, 1960 Variety group from V. corymbosum × V. angustifolium
'Blue and white sugar grape' Germany, k. A. Variety group from V. corymbosum × V. angustifolium
'Blue and White Record' Germany, 1958 Selection from blue-white sugar grapes
'Bluecrop' USA, 1952 ('Jersey' × 'Pioneers') × ('Stanley' × 'June')
'Bluerose' Australia, k. A. k. A.
'Bluetta' USA, 1968 ('North Sedgewick Lowbush' × 'Coville') × 'Earliblue'
'Coville' USA, 1949 ('Jersey' × 'Pioneers') × 'Stanley'
'Denise Blue' Australia, 1978 Free flowering of 'Late Blue'
'Duke' USA, 1987 ('Ivanhoe' × 'Earliblue') × 192-8 (E-30 × E-11)
'Earliblue' USA, 1952 'Stanley' × 'Weymouth'
'Elizabeth' USA, 1966 ('Kathrine' × 'Jersey') × 'Scrammel'
'Gila' Germany, k. A. k. A.
'Greta' Germany, k. A. k. A.
'Maru' New Zealand, 1991 Open flowering of 'Premier' (Rabbiteye)
'Nui' New Zealand, 1988 ('Ashworth' × 'Earliblue') × 'Bluecrop'
'Patriot' USA, 1976 ('Dixi' × 'Michigan LB1') × 'Earliblue'
'Polaris' USA, 1996 k. A.
'Rahi' New Zealand, 1991 Open flowering of 'Premier' (Rabbiteye)
'Reka' New Zealand, 1988 ('Ashworth' × 'Earliblue') × 'Bluecrop'

Cultivated blueberry cultivation

Blueberry plantation in Plainville, New York

The natural habitats of Vaccinium species are acidic, nutrient-poor, humus-rich bog and sandy soils . The different varieties place different demands on the soil according to the demands of their parent species and the same conditions do not apply to all. Furthermore, the genetic makeup of cultivated blueberries comes from species whose natural range in North America extends over several climate zones. The climatic requirements of the various selections are correspondingly different. Cultivated blueberries cannot be grown in any region, neither in North America nor in Europe. However, it is possible to specifically create varieties for different climatic zones, so that suitable varieties can be grown in Europe from Norway to Spain.

Floors

With regard to the physico-chemical properties of the soil, a high proportion of air-carrying coarse pores are required for growing blueberries. Furthermore, the moisture penetration must be uniform over the course of the year. The pH values ​​should be low, i.e. in the acidic range (optimally between 4 and 4.5). The proportion of organic matter should be high (around 4 to 5% humus content). Studies have shown that the vegetative growth of various breeds is strongest at pH values ​​below 5 and that it decreases linearly with an increase in pH. Furthermore, experience reports show that the growth of blueberry plants on peat can apparently be significantly improved. Alternatively, sawdust and bark material should have a positive effect on root development.

Blueberries depend on a consistently high level of soil moisture. They do not have special adaptations to changing humidity conditions, so that high water losses and leaf damage can quickly occur in dry conditions. The high density of the stomata on the underside of the leaves of 500 to 600 / mm² promotes evaporation losses. Eventually, flower buds die off and there is no need to plant new flowers. In contrast, floods are apparently tolerated to a certain extent. The flooding tolerance is said to be due, among other things, to the formation of enlarged epidermal cells , which are supposed to act like an aerenchyma (= air-filled tissue). The bark of the stems should also form enlarged cells when they are flooded. Under waterlogged leaves, the leaves have larger intercellular spaces (= air-filled cell spaces) in the sponge tissue to facilitate the oxygen supply. However, if the tolerance limit is exceeded, damage occurs. The first symptoms are leaf yellowing and reddening, leaf shedding and death of the shoot tips. Phytophthora root rot is also more common in wet conditions .

Due to the lack of root hairs, the water and nutrient absorption of the Ericaceae root system is limited. In adaptation to their natural, nutrient-poor and often wet locations, the representatives of the heather family therefore live in a mutually beneficial community ( symbiosis ) with soil-borne fungi, the mycorrhiza . The fungi provide the plant with nutrient salts and water and in turn receive part of the assimilates generated by the photosynthesis of the plants . For example, a possible fungus Pezizella ericae is almost always present in the soil of natural occurrences, but not in plant substrates and soils that have been used for arable farming for a long time. In cultivated blueberries in Europe, mycorrhiza were not found in every plant tested. pH values ​​above 5 seem to suppress the successful colonization of the blueberry roots. Furthermore, the degree of colonization of the roots seems to decrease with increasing amounts of nitrogen. Despite numerous studies, no clear effect of soil fungi on the growth and fruit quality of cultivated blueberries could be proven.

With regard to the fertilization of cultivated blueberries, experiences differ widely. Blueberries are considered to be extremely sensitive to salt, which is why excessive doses can have negative effects. The nutrient content of the leaves is generally used to estimate the required amount of fertilizer . Supplemented by soil analyzes and the nutrient withdrawal by the fruits, conclusions can be drawn about the nutrient requirements of the plants. Recommendations are based on fertilizing the main nutrients nitrogen , phosphorus and potassium in a ratio of 3: 1: 2. Besides have magnesium , copper and zinc significance for the main diet of blueberry plants. The weighting of the individual nutrients in relation to one another essentially depends on the special conditions of the planting and the observation skills of the farm manager.

climate

For the cultivation of blueberries, the distribution of precipitation over the course of the year is more important than its amount. The shallow roots are particularly sensitive to drying out. The soil in the root area must be evenly moistened. Therefore, additional irrigation may be necessary, for example in summer drought. Drought during flowering leads to a weak or damaged fruit set, with only a few berries developing; Parts of the fruit set remain empty. Cultivated blueberries need full sunlight for good growth and the development of high fruit quality. In contrast to the forest blueberries ( Vaccinium myrtillus ) native to Central Europe, they do not tolerate shading. In exposed locations, strong winds can damage the young fruits by rubbing them against each other and also lead to high water losses through evaporation . Excessive evaporation in winter causes the shrubs to become supercooled, which can lead to frost damage. Protection from the wind by hedges or strips of trees is therefore part of improving the location factors in cultivated blueberries .

Plant protection

Flower bug ( Orius insidiosus ) as a potential beneficial insect in blueberry cultures sucks on scale insects.
Little frost moth ( Operophtera brumata ) caterpillar as a potential pest on blueberry bushes by eating on buds, flowers and leaves.

Cultivated blueberries have only recently been grown in Europe, so their natural enemies are hardly present. The cultivated blueberry is therefore still regarded as a so-called healthy fruit, which hardly requires intensive plant protection measures. In contrast, a number of plant diseases and a number of pests are known from North America . In Europe, the first signs of disease and pest pressure can be observed through the introduction of pests from North America. In addition, the cultivated blueberries are affected by native pests. Chemical agents such as insecticides and fungicides are used as measures against harmful pathogens . Meanwhile, preventive control (biological control) is increasingly finding its way into cultivated blueberry cultivation in North America, which is already being carried out in many places in European agriculture in integrated cultivation. The natural enemies of the harmful insects ( beneficial organisms ) are specifically promoted on the cultivated areas by their host plants (food, egg-laying area) being settled on the cultivated areas. These beneficial insects consist of predators and parasitoids . The predators, such as flower bugs of the genus Orius (e.g. Orius insidiosus ) or ladybirds (Coccinellidae) feed mainly on soft-skinned, potential pest insects of all stages of development on blueberries. Different arachnids also eat larger insects. Parasitoids, on the other hand, lay their eggs in the adult insect pests or their larvae and thus cause their death. These include parasitic wasps (Ichneumonidae) and brackish wasps (Braconidae).

In Europe, it is mainly insects and fungi that can cause crop losses. This includes the small frost weaser ( Operophtera brumata ) , which has since been carried off to North America . Its caterpillars bore into the buds and hollow them out and also eat the flower organs. More butterflies may cause damage to leaves and fruit damage to the blueberry bushes whose herbivory are curlers - and owl species . The larvae of the gall mosquito Prodiplosis vaccinii introduced from North America suckle at the shoot tips. These roll up, change color and finally die. The result is new growth and, associated with this, undesirable premature branching. To the lid scale insects belonging San José Scale ( Quadraspidiotus perniciosus ) was introduced from East Asia over North America to Europe. It creates growth depressions (atrophy) of the bushes. As a result of the high production of honeydew , black fungi (Dematiaceae), for example of the genus Alternaria, appear on leaves and fruits. The tube aphid (Aphididae) Ericaphis fimbriata also comes from the USA. It produces a lot of honeydew. This leads to contamination of the fruit.

In some blueberry varieties, resistances to diseases appear, which are increasingly being taken into account in breeding. The following diseases ( mycoses ) caused by fungi can play a role under Central European conditions: Blossom and fruit rot ( gray mold ; Botrytis cinerea ) occurs in damp weather. The infection takes place in the flowers. These will turn brown and later a gray mushroom lawn will appear. The inflorescences clump together and entire shoots can die. The twig and fruit monilia ( Monilinia vaccinii-corymbosi ) is also promoted by damp weather. Infected parts of the plant wilt and eventually die, turning black-brown. The fungus was first detected in Europe (Austria) in 2002. The Godronia shoot death ( Godronia cassandrae ) was introduced from North America and is becoming more common in European plants. It causes branches and shoots to die off. The fungus overwinters in cancerous infection sites. The shoots initially turn reddish-brown, then they die.

Other diseases in blueberries are caused by plant viruses and bacteria . For example, the virus known as “shoestring disease” in North America is caused by the Blueberry shoestring virus (BSSV) from the genus Sobemovirus and is transmitted from bush to bush by the sucking activity of the tube aphid Illinois pepperii . The disease initially causes a ribbon-like deformation of the leaves. As a result, the plants are weakened and the blue color of the fruits is impaired. The bacterium Agrobacterium tumefaciens invades through injuries and causes stem gall . The plants grow abnormally and eventually wither.

Mammals such as voles, rabbits and other game can cause damage to the bushes. Game protection fences are used against wild mammals. The berries are also food for numerous bird species. Especially starlings can lead to considerable harvest losses, which can be restricted by bird nets.

Multiplication

Cultivated blueberries can be propagated both by seeds and by vegetative methods ( plant propagation ). Seedlings play a subordinate role in cultivation because the varietal character is lost and seedlings take years to bloom. On the other hand, growing seedlings is of great importance for breeding. First and foremost, cultivated blueberries are propagated for commercial cultivation using cuttings . Both green cuttings and cuttings (shoot cuttings) are obtained from selected mother plants and placed in a growing medium. The rooting is different depending on the variety and can take eight to 15 weeks. Rooting can be accelerated by heating the growing medium and using rooting preparations. The cuttings are obtained in greenhouses or in film tunnels at 25 to 30 ° C. The water supply for the cuttings is ensured through high humidity and also through spray mist systems .

harvest

Mechanical blueberry harvest (wild form) in New Brunswick , Canada

The cultivated blueberries are harvested over a period of around twelve weeks. According to American studies, the bushes produce yields of 1 to 1.5 kg of fruit per bush in the first few years. In full yield , they should produce around 3 to 5 kg. Individual bushes can provide up to 20 kg of berries.

The hand harvest provides the best quality. Ripe, uniform and undamaged fruits for the fresh market can be picked directly into the sales container. With almost all varieties, it is necessary to pick the plants several times, as the berries ripen at different times. The berries are carefully picked without wiping off the white frost. One picking force can handle around 4 to 8 kg of blueberries per hour.

In the larger plants in the USA and Canada, special harvesting machines have found their way, which are more cost-effective. However, they provide fruits that are primarily suitable for processing. They are pulled by a tractor or are self-propelled, moving over the bushes ("over-the row machines"). The berries are separated from the bushes by shaking, beating or scraping. This leads to mechanical damage and the harvest of unripe fruits. However, technical progress enables ever gentler harvest, so that the share for the fresh market is increasing.

Marketing and Production

Around half of the German cultivated blueberry harvest is sold directly from the farm, via weekly markets or in self-picking facilities. The rest is bought from wholesale markets or processors through contract cultivation or through producer groups . In North America, 10% of the harvest is sold through self-picking. 90% are marketed in equal parts as fresh goods or sent for processing.

The marketing strategies include large blueberry festivals, especially in the USA. In the cultivation countries, they are usually carried out by producer groups. In addition to promoting sales , these festivals often serve tourist purposes. Blueberry festivals are also held in Germany to increase awareness of the fruit and to promote sales. They are organized by the companies themselves, producer groups or marketing companies. Here, too, the tourist component is used, every year a blueberry queen is elected in Walsrode in the Heidekreis district, who takes on national representative tasks. It is supposed to advertise the peculiarities of their homeland and the quality of local products.

It is difficult to determine how high the global production of Vaccinium fruits is in total. Many different species are included in the statistics under the name “Blueberry”. In many cases, no distinction is made between cultivated blueberries and cranberries. In addition, the figures include the harvest from wild stocks. Estimates assume a world harvest of between 300,000 and 400,000 t. The front runner in blueberry production is the USA with 55% of the world harvest; Canada follows with 28% and Poland with 10% (average for the years 2000 to 2002, including wild populations of V. angustifolium and V. macrocarpon and other species). The states of Michigan and Maine account for more than half of US production. While in Maine almost exclusively wild stocks are harvested, in Michigan mostly cultivated blueberries are grown and harvested. Larger cultivated blueberry plantations can also be found in the states of New Jersey, Oregon, Georgia, North Carolina, Washington, California, Florida and Mississippi.

Areas and yields in blueberry cultivation in the USA in 2006:

State He wears) Area (ha)
Michigan 40,822 7,325
New Jersey 23,586 3,075
Oregon 16,147 1,780
Georgia 14,288 2,832
North Carolina 11,566 1,902
Washington 8,618 1,376
California 4,536 930
Florida 3,175 1,052
Mississippi 2,086 930
Indiana 1,542 250
new York 907 283
Arkansas 726 214
Alabama 145 109
total 128.145 22,058

A notable cultivation with significant increases in area and harvest occurs in Chile and Argentina, among others. The cultivation of cultivated blueberries in the southern hemisphere enables a year-round supply of fresh produce, so-called “off-season fruits”.

In Europe, cultivation of blueberries is concentrated in Poland and Germany. Significant increases in area are expected in Poland and Spain in the coming years.

2004 2005 2006
country Ha t Ha t Ha t
Germany 1,500 8,000 1,600 7,000 1,800 8,000
Poland 1,500 3,750 1,700 3,750 1,800 5,000 to 8,000
France 300 1,500 300 1,700 300 1,700
Netherlands 300 1,500 330 1,650 370 1,650
Spain 150 900 200 1,000 300 1,600
Italy 160 800 180 800 180 1,200
Belgium 45 162 48 170 48 250
Portugal 40 200 40 200 40 250
total 3,995 16,812 4,398 16,270 4,838 18,650

Ingredients and health value

Blueberry
smoothie , a "trendy drink" originating in the USA

When it comes to sugars, glucose (48%) and fructose (49%) predominate in cultivated blueberries . Sucrose is only 3%. The acid content is citric acid , malic acid and quinic acid in a ratio of approx. 8: 1: 1. In wild blueberries the ratio is around 3: 1: 3.

Ingredients of the fruits of cultivated blueberries (per 100 g fresh mass):

ingredient salary ingredient salary
Calorific value 250 kJ (60 kcal ) iron 0.17 mg
water 83 g manganese 0.28 mg
protein 0.6 g zinc 0.11 mg
fat 0.5 g copper 0.06 mg
carbohydrates 14 g selenium 0.6 µg
citric acid 0.9 g Polyphenols 0.25 mg
cellulose 1 g Vitamin A 100 IU
potassium 90 mg Vitamin B1 (thiamine) 0.04 mg
calcium 13 mg Vitamin B2 complex 6.84 mg
phosphorus 10 mg Vitamin B6 0.036 mg
magnesium 7 mg vitamin C 13 mg
sodium 2 mg Vitamin E. 1.00 mg

The health value of fruits is seen, among other things, in being able to switch off harmful oxygen radicals in the human body during stress or illness ( oxidative stress ). Phenols (0.5 to 2.5 mg / g fresh weight) and anthocyanins (1 to 3 mg / g fresh weight) are of interest in this context . Anthocyanins are water-soluble, blue to red plant pigments that are found exclusively in the fruit peel of cultivated blueberries. The higher the phenol content and the more colorants there are in the fruit, the higher the antioxidant potential . The Oxygen Radical Absorbance Capacity (ORAC) is given in Trolox equivalents (µmol TÄ). The content of cultivated blueberries is estimated at around 25 µmol TÄ / g fresh weight. According to American studies, blueberries are among the fruits with the highest stress-relieving effect. The consumption of blueberries is said to reduce the risk of cancer. The absorbing effect of blueberries is also said to stabilize the immune system of humans and to prevent cardiovascular diseases and strokes .

Use and storage

Blueberry muffin

Cultivated blueberry bushes play a subordinate role as pure ornamental trees due to their special location requirements. As a supplier of berries, however, they are of great importance as food . The increasing area under cultivation worldwide and the rising demand are signs of their growing popularity. The per capita consumption of fresh produce by Germans is around 100 g per year, while per capita consumption in the USA is significantly higher at 370 to 570 g per year. Cultivated blueberries are used fresh in fruit salads, baked goods such as muffins , pancakes, blueberry cakes or tarts, in dairy foods such as quark or yoghurt, compote or cold dishes, and dried in muesli or fruit bars. Cultivated blueberries are ideal for jellies or jams , because their pectin content makes them gel particularly well. Blueberries are also a good basis for juices and nectars , alone or in combination with other fruits.

Fresh blueberries can be frozen without any problems, and the product hardly suffers any loss of quality. Frozen fruits have a very long shelf life and can almost always be used instead of fresh produce in the kitchen. The storage of fresh berries, however, is limited. Blueberries do not form a clear dividing tissue, so that when the fruit is detached, depending on the variety, a more or less large wound occurs. This reveals vascular connections and parts of the epidermis. These scars allow microorganisms to penetrate, which eventually lead to fruit rot . In the case of Rhizopus soft rot ( Rhizopus nigricans ), the infected fruits quickly become soft and lose juice. The effective method to prevent fungi from penetrating is to cool to temperatures below 10 ° C as soon as possible after harvesting, so that the fungi can no longer grow. When the fruit ripens, blueberries show increased fruit respiration; they are climacteric fruits. The higher the fruit respiration, the less it can be stored. Here, too, cooling is essential. By lowering the storage temperature from 20 to almost 0 ° C, the fruits of most varieties can be stored up to eight times longer. While cultivated blueberries of the 'Bluecrop' variety can be kept for around a week without refrigeration, this can be extended to around seven weeks at a storage temperature of around 0 ° C. The storage period can be significantly increased again by lowering the oxygen content of the air to around 2 to 3% and increasing the CO 2 concentration to 8 to 12%.

Invasiveness of the blueberry bush

Cultivated blueberries easily grow wild from their cultivation areas into the surrounding area. The fruits are eaten by birds and mammals; the seeds are excreted in the feces in other places ( endochory ). In this way, new plants can establish themselves at suitable locations, which can form dense stands through vegetative reproduction .

In Germany, the hybrid Vaccinium angustifolium × Vaccinium corymbosum (syn. V. × atlanticum ), which is known as the shrub blueberry or cultivated blueberry, is a so-called invasive species . Shrub blueberries show a great variability of characteristics. A number of specimens are close to one of the parent species in their appearance, transitions in all characteristics between the two species are just as common. In Austria it is classified as potentially invasive. Overwilding has also been known from the Netherlands since 1949. The blueberry bush has a multitude of direct and indirect ecological effects on other species, communities or biotopes outside of the cultivation areas , especially in near-natural raised bog remnants of north-western Europe. The spread of the blueberry bush has only recently been observed, so its distribution is still incompletely known. It occurs in 20 districts in Lower Saxony . In the southern Lüneburg Heath, extensive naturalization is known that exceeds the total area by 14 times. In the course of about 50 years, distances between cultivation areas and spontaneous emergence of the shrub blueberry of about 2 kilometers have been achieved. It grows wild in pine forests and wetlands in the vicinity of the cultivated areas.

The overgrowths can form dense stands. In pine forests , dense shrub layers emerge from these , which displace the ground vegetation through shading. So far, no endangered species have been affected here. The impenetrable shrub layers can hinder forestry work. The striking autumn color of the blueberry bushes, on the other hand, increases the attractiveness of the otherwise slightly monotonous forest areas.

Raised moors are sensitive, endangered and legally protected biotopes. Here the edge areas as well as pitted and drained areas are affected, especially areas with near-natural vegetation. In the de- and regeneration stages of the raised bogs, the shrub blueberry displaces the vegetation typical of the bog through competition with light. Almost all raised bog species in Germany are endangered or threatened with extinction, albeit generally due to urbanization and not due to the wilderness of the bilberry. In the “bog in the Schotterheide”, no more typical bog species could be found under an umbrella of 90 to 95% coverage of the bilberry; under a coverage of 70% the typical bog species were displaced apart from the smallest remains. In addition, the degeneration of partially drained moors can be accelerated by the blueberry bush; the increased evaporation of the plant cover accelerates the drying out of the moors.

According to the Federal Nature Conservation Act , the application of alien plants is generally not permitted without a permit. So far feral growth has only occurred in the vicinity of plantations . In order to protect the valuable bog vegetation from the penetration of the blueberry bush, it makes sense to keep a minimum distance of three kilometers between new plantations and bogs. Moors, which are nevertheless threatened by overgrowth, should be protected from other endangering factors such as drainage and peat , because these would encourage the immigration of the blueberry bush. So far there is no experience with the control of the blueberry bush. Due to their high regenerative capacity, simply cutting the plants is not enough. In contrast, it would rather lead to an increase in the density of shoots. A complete excavation of the plants can be successful, whereby the strong disturbances of the sensitive biotopes and the side effects on the bog vegetation are to be avoided.

swell

The information comes from the following literature:

Main literature

  • Georg Ebert: Cultivation of blueberries and cranberries. Praktiker series, Ulmer-Verlag, Stuttgart 2005, ISBN 978-3-8001-4420-4 .
  • Mark Rieger: Blueberries - Vaccinium spp. , University of Georgia , URL , last updated August 2006, accessed March 2008.
  • Mark Longstroth: A Year in the Life of a Blueberry Bush , Michigan State University 2000 URL , last updated in 2003, accessed March 2008.
  • U. Starfinger & I. Kowarik: Vaccinium angustifolium × V. corymbosum (Ericaceae), cultivated blueberry. PDF , species profile in the Neo Flora , last update August 2007, accessed in March 2008.

The following sources are cited for additional information:

Individual evidence

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  15. ^ DC Ramsdell: Blueberry diseases in Michigan. Michigan State University Extension Bulletin E-1731, as of 2000, URL ( Memento of the original from October 11, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , accessed March 24, 2008. @1@ 2Template: Webachiv / IABot / web1.msue.msu.edu
  16. http://www.n-tv.de/996555.html accessed on January 21, 2009.
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Web links

Commons : Blueberries  - Collection of images, videos and audio files
Wiktionary: bilberry  - explanations of meanings, word origins, synonyms, translations
This article was added to the list of excellent articles on April 26, 2008 in this version .