The European blueberry (Vaccinium myrtillus L.) and the potential for cultivation. A review

Abstract

Blueberries belong to the genus Vaccinium, a widespread genus with more than 200 species of woody plants. In Northern Europe, the European blueberry (EB), also called bilberry, is one of the most important wild berries. EB (Vaccinium myrtillus) is very demanded by the processing industry, due to its delicious taste and high dietary value. However, to our knowledge there has been made no efforts of domestication of the species, and it is still harvested in forest fields without any cultivation. The successful management of the sweet lowbush blueberry (V. angustifolium), which in many ways is similar to the EB, suggests that there are opportunities to increase yield and decrease the significant yearly variation in EB yield, by practices including fertilization, irrigation, cutting trees, and weed control. The fruit yield in wild stands of EB is very variable, but the potential is probably close to 2 tons per hectare. Results from literature on growth of the EB, development and ecology are discussed in relation to possibilities for domestication.

Full text

Received: 21 April, 2010. Accepted: 29 July, 2010. Invited Review
The European Journal of Plant Science and Biotechnology ©2011 Global Science Books
The European Blueberry (Vaccinium myrtillus L.)
and the Potential for Cultivation. A Review
Rolf Nestby1* • David Percival2 • Inger Martinussen3 • Nina Opstad4 • Jens Rohloff5
1 Norwegian Institute for Agricultural and Environmental Research, Grassland and Landscape Division, Kvithamar, 7500 Stjørdal, Norway
2 Department of Environmental Sciences, Nova Scotia Agricultural College, Truro, Nova Scotia, Canada
3 Norwegian Institute for Agricultural and Environmental Research, Arctic Agriculture and Land Use Division, Box 2284, 9269 Tromsø, Norway
4 Norwegian Institute for Agricultural and Environmental Research, Arable Crops Division, Kapp, Norway
5 The Plant Biocentre (PBC), Department of Biology, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
Corresponding author: * rolf.nestby@bioforsk.no
ABSTRACT
Blueberries belong to the genus Vaccinium, a widespread genus with more than 200 species of woody plants. In Northern Europe, the
European blueberry (EB), also called bilberry, is one of the most important wild berries. EB (Vaccinium myrtillus) is very demanded by
the processing industry, due to its delicious taste and high dietary value. However, to our knowledge there has been made no efforts of
domestication of the species, and it is still harvested in forest fields without any cultivation. The successful management of the sweet
lowbush blueberry (V. angustifolium), which in many ways is similar to the EB, suggests that there are opportunities to increase yield and
decrease the significant yearly variation in EB yield, by practices including fertilization, irrigation, cutting trees, and weed control. The
fruit yield in wild stands of EB is very variable, but the potential is probably close to 2 tons per hectare. Results from literature on growth
of the EB, development and ecology are discussed in relation to possibilities for domestication.
_____________________________________________________________________________________________________________
Keywords: aerial shoot, buds, cultivation, flowers, fruits, rhizome
CONTENTS
INTRODUCTION.......................................................................................................................................................................................... 5
VACCINIUM – SYSTEMATICS.................................................................................................................................................................... 7
PLANT CHARACTERISTICS...................................................................................................................................................................... 7
Rhizomes and roots ................................................................................................................................................................................... 7
Aerial shoots.............................................................................................................................................................................................. 8
BUD DEVELOPMENT AND FLOWER INDUCTION ............................................................................................................................... 8
POLLINATION AND FRUIT DEVELOPMENT.......................................................................................................................................... 8
FRUIT CHARACTERISTICS....................................................................................................................................................................... 9
POTENTIAL OF ENHANCING PLANT DEVELOPMENT AND FRUIT YIELD BY MANAGEMENT ................................................. 9
Half cultivation.......................................................................................................................................................................................... 9
Forest cutting........................................................................................................................................................................................... 10
Climate .................................................................................................................................................................................................... 10
Soil and nutrition..................................................................................................................................................................................... 11
Insects...................................................................................................................................................................................................... 11
Diseases................................................................................................................................................................................................... 11
Weeds ...................................................................................................................................................................................................... 12
Browsing animals and birds feeding on the berries ................................................................................................................................. 12
Cultivation on farm land.......................................................................................................................................................................... 12
REPRODUCTION....................................................................................................................................................................................... 12
Seeds........................................................................................................................................................................................................ 12
Vegetative propagation............................................................................................................................................................................ 13
HARVEST AND DELIVERY...................................................................................................................................................................... 13
CONCLUSION............................................................................................................................................................................................ 13
REFERENCES............................................................................................................................................................................................. 14
_____________________________________________________________________________________________________________
INTRODUCTION
The European blueberry (EB) is a deciduous woody dwarf
shrub, typical and abundant especially in spruce- and pine-
dominated heath forests of medium fertility in the northern
hemisphere (Fig. 1).
EB also grows in marginal types of forests, and above
the tree limit up to high altitudes. Typically, it grows on
areas of better-drained acid soils. The tiller (individual
shoot from the rhizome) develops into an axis (a system of
annual shoot increments formed by the branching of the
original tiller or subsequently, by the branching of a shoot
arising from the lower part of this; of limited longevity)
from approximately 5 to 90 cm high depending on climate
and nutrient availability (Flower-Ellis 1971). The bush,
consisting of abundant tillers, is perennial and deciduous,
and leaves are notably bright green, 1-3 cm long, slightly
toothed and not leathery. Tillers and leaves are hairless and
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The European Journal of Plant Science and Biotechnology 5 (Special Issue 1), 5-16 ©2011 Global Science Books
can by this be distinguished from other members of the
heather family or any other moorland or mountain shrub
even without flowers and fruit. It plays a significant role for
a number of other species, particularly of birds and mam-
mals, and its abundance has been used as an indicator of
biodiversity within the forests. The EB has long had an im-
portant role in human cultures; the nutrient rich berries
providing food, and used as a herbal remedy for digestive
problems, diabetes and to strengthen capillaries in the cir-
culatory system. The juice of the berries has also been used
as a dye, providing a blue colour for both linen and paper
(Featherstone 2002).
Cultivation of Vaccinium spp. is not a new approach
within horticulture. Blueberry cultivation is thought to have
started when Native Americans burned wild stands of low-
bush blueberries (V. angustifolium Ait. and V. myrtilloides
Michx.) to tend them and to increase production (Strik
2006). More advanced blueberry domestication began in
New Hampshire in 1908 by the United States Department
of Agriculture (Janes and Percival 2003). Since the 20th cen-
tury American blueberry species and varieties have been
spread to Europe (Nyström 1932; Kühn and Vang-Petersen
1991; Gough 1996; Hjalmarsson 2006). Some of the know-
ledge achieved from the very successful domestication of
highbush blueberry species, could be transferred to the pot-
ential cultivation of the European blueberry (EB). However,
the approaches and associated technologies developed with
the sweet, lowbush blueberry (V. angustifolium) in North
America, may present an increased likelihood of success.
This plant is comparable in many ways to V. myrtillus, with
similar growth, morphological characteristics (e.g., exten-
sive root and rhizome system), berry size, coloration and
good winter hardiness.
Domestication of the lowbush blueberry began in Maine
in the 19th century, and the blueberry industry has since
undergone a significant increase. In 1990, the industry had
over 1000 producers and the lowbush blueberry acreage and
production were respectively 113 000 ha (Kinsman 1993)
and 12 700 tons, compared to 477 tons in 1951. In 2008 the
production was increased further and was approximately
113 000 tonnes (Percival 2010 pers. comm.). The size of
individual producer operations varies from one to over 10
000 ha. Most commercial fields have been developed from
abandoned farmland and woodlands that were deemed to
have substantial lowbush blueberry plants present after tree
removal. Although lowbush blueberry cultivars have been
developed, the crop in Maine, the Canadian Maritimes, and
Quebec is almost entirely produced by genetically diverse
wild clones (Aalders et al. 1979; Hall 1979; Chen et al.
1998). To make a similar success history in an industry
based on the EB may be difficult, as EB are a dwarf shrub
that produce single or paired berries on the bush instead of
clusters, and consequently have relatively low yields. How-
ever, the demand for quality fruit of EB is strong due to a
high content of valuable biological compounds (Halvorsen
et al. 2002; Riihinen et al. 2008).
The EB is a calcifuge plant that is circumboreal in dis-
tribution. It occurs in Europe, the northern parts of Asia,
including Japan, and also in Greenland (Fig. 1) where it is
thought to be introduced from Europe, possibly in Viking
times (Featherstone 2002). In Europe it is still harvested in
rural areas by the local population (Pardo de Santayana et al.
2005; Konovalchuk and Konovalchuk 2006; Coudun and
Gegout 2007) for household consumption and recreational
purposes (Kangas and Markkanen 2001), and is one of the
economically most important wild berry species in Finland,
Norway and Sweden (Kangas 2001). For the industry in
Sweden, Finland and some Central and East European
countries EB are hand harvested by combing the plants in
cut forestland. Intensive forestry with clear-cuttings and soil
preparation has been observed to give a more even distribu-
tion of the different age classes and to decrease the cover-
age of EB (Kardell and Eriksson 1995; Miina et al. 2009).
On the contrary, Nielsen et al. (2007) found that EB pro-
duction and growth decreased with increased forest maturity.
Therefore, for a stable and possibly increasing supply of
berries to the EB industry, there is a need to develop an
improved and more scientifically based production system
Fig. 1 Distribution of EB in the Northern hemisphere (Hultén and Fries 1986), with the kind permission of Sven Koeltz (Dnr 70-79/1998).
6

European blueberry domestication. Nestby et al.
in which consistent, high yielding crops of EB with excel-
lent quality attributes are produced with manageable input
costs (e.g. harvesting costs, cost for transportation and
logistics). Several aspects need to be taken into considera-
tion in developing an improved production system, either
growing EB on abandoned farmland, or by half-cultivation
on cut forestland.
To our knowledge, there have been no prior systematic
examinations of how to domesticate the EB by half-cul-
tivating forest fields or by growing on farm land. There are
however, numerous publications discussing the biology and
ecology of EB in forest ecosystems, and how its distribution
is affected by natural disturbances and forest cultivation.
The objective of this paper is to present an overview of rele-
vant work dealing with EB, and relate it to possibilities for
cultivation. The sweet lowbush blueberry will be the bench-
mark model used since it is highly domesticated and has
been thoroughly examined for reactions to environmental
conditions (Kinsman 1993; Jeliazkova and Percival 2003b).
VACCINIUM – SYSTEMATICS
The genus Vaccinium consists of woody, perennial shrubs in
the heath family (Ericaceae) and contains, among other spe-
cies, both the European and the American blueberry (Tab l e
1). Although the EB is often referred to as the bilberry, this
includes several species of low-growing shrubs in the genus
Vaccinium that bears fruit. The term European blueberry
(EB) will be used throughout this article since it points
directly to V. myrtillus and defines it as a blue berry which
is mirrored in most European languages. Other names are
blåbær (Scandinavian), blaeberry (Britain), whortleberry
(Britain), whinberry (or winberry, Britain), wimberry, myr-
tle blueberry, heidelbeere (Germany), blaubeere (Germany),
fraughan (Ireland), myrtilli (Italian) and other names regi-
onally (Lid 1963; Tirmenstein 1990; Featherstone 2002;
Wikipedia 2009a). The European and the American blue-
berry species belong to different sections, and while the EB
belongs to the section Myrtillus together with 11 other spe-
cies of minor importance, the American blueberries belong
to the section Cyanococcus (Ta b l e 1). The EB is a shrub
varying in size from approximately 5 to 90 cm, and chro-
mosome number is 2n=24 (Hagerup 1928; Hedberg and
Hedberg 1961; Tirmenstein 1990; Vander Kloet and Dickin-
son 1999; Featherstone 2002). The American blueberries
vary in size from approximately 10 to 400 cm with the
smaller species known as "lowbush blueberries" (typically
less than 1 m in height) and the larger species as "highbush
blueberries". The flowers of both sections are bell-shaped,
white, pale pink or red, sometimes tinged greenish. How-
ever, while the EB grow one (rarely two) flower from a leaf
axil bud, the American blueberries can produce an inflores-
cence containing a cluster of berries from a leaf axil bud.
Highbush and lowbush blueberries develop relatively large
clusters of berries mainly on one-year-old wood but also
some on two and three year old wood, producing greater
yields than huckleberries. Western huckleberries are in dif-
ferent taxonomic sections (Myrtillus, Vaccinium, and Pyxo-
thamnus) than highbush and lowbush blueberries (Cyano-
coccus). Sections Vaccinium and Pyxothamnus each contain
one species. Some species are found not only in North
America, but also in Europe, Asia, and Greenland (Barney
2008). The two species V. uliginosum (Bog bilberry) and V.
vitis-idaeus (lingonberry) grow frequently under the same
environmental conditions in the north of Europe as EB, and
belong to the sections Vaccinium and Vitis-idaea respec-
tively.
PLANT CHARACTERISTICS
Rhizomes and roots
The characteristics and growth pattern of EB are well docu-
mented in the work of Flower-Ellis (1971). EB growth pat-
tern is rhizomatous and it usual forms open colonies or pat-
ches in the vegetation that can be as large as 15 m in dia-
meter (Ritchie 1956). A characteristic form of the bilberry
stand is that of an irregular, approximately circular patch,
with an increase in rhizome age from the distal of the stand
to the centre (Flower-Ellis 1971). The growth direction of
rhizomes is mainly centrifugal, but soil factors strongly
affect rhizome growth directions so density and rhizome
growth and diameter growth is not necessarily correlated.
Rhizomes up to 5.5 m long have been found, with an ave-
rage length of 2.0 m (Albert et al. 2003), and one single
clone may occupy several square meters (Flower-Ellis
1971). The branching of the rhizome is sympodial and the
aerial shoot disposition is reflected by this. Typically, from
their originating point two rhizomes extend 20-30 cm
underground without branching before dividing, ideally into
two, occasionally into three or more, of which the middle
one is the most vigorous. This middle rhizome turns up-
wards and develops a green shoot or continues its growth
underground. After a further 20-30 cm it divides into a
group of shoots which corresponds morphologically with
the green aerial shoot. Thus the rhizome in EB ends in a
green shoot or in a corresponding group of rhizomes. Fur-
ther growth is continued by two side branches. Along a seg-
ment of rhizome, aerial shoots tend to arise at intervals of
20-30 cm (Flower-Ellis 1971). EB rhizomes can live for up
to 34 years, although rhizomes older than 15 years rarely
produce new aerial shots or rhizomes. A concern that has
sometimes surfaced in wild blueberry growth is stagnation
of growth caused by a lack of rejuvenation of the rhizome
system (Percival 2010 pers. comm.).
The quantity and size of clones (one rhizome and
shoots/axis originating from it) may vary significantly, even
within the same population (Albert et al. 2004). Nutrient
mobilization and reallocation typically occurs in the autumn
with nutrients mowing from the leaves to the rhizomes, and
this is the main time for rhizome growth, along with the
spring (Featherstone 2002). New roots are mainly found in
late summer and in autumn, and outside this period no im-
portant root formation occurs, even in late spring and early
summer, when new aerial vegetation develop and flowering
take place (Bonfante-Fasolo et al. 1981). However, given
Table 1 The systematic link between European and American blueberries.
Order Ericales
Family Ericaceae
Subfamily Vaccinioideae
Tribe Vaccinieae
Genus Vaccinium Section Important species of section
Batodendron, Brachyceratium, Bracteata, Calcicolus, Ciliata,
Cinctosandra, Conchophyllum, Cyanococcus, Eococcus, Epigynium,
Hemimyrtillus, Herpothamnus, Myrtillus, Neurodesia, Oarianthe,
Oxycoccoides, Oxycoccus, Pachyanthum, Polycodium,
Pyxothamnus, Vaccinium, Vitis-idaea.
Myrtillus
V. myrtillus
Cyanococcus
V. corymbosum
V. angustifolium
V. myrtilloides
V. virgatum (ashii)
V. darrowi
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The European Journal of Plant Science and Biotechnology 5 (Special Issue 1), 5-16 ©2011 Global Science Books
the symbiotic nature of the fine roots with mycorrhizal
fungi, there is probably always some level of new root
growth and development occurring (Percival 2010 pers.
comm.).
Aerial shoots
Aerial shots of EB arising from the same rhizome system
have similar characteristics and are referred to as ramets
that together with the rhizome, originate from and form a
blueberry clone (Fig. 2). The resulting entity of ramets/axes
of one clone, form a bush (Flower-Ellis 1971).
However, EB has high morphological plasticity, and
growth habit in terms of e.g. branching can differ greatly
between habitats as a response to environmental differences
(Tolvanen 1994). EB aerial shoots grow more vertically and
have lower branching angles in open habitats compared
with the forest. The stems are angled and woody, and the
continuous rejuvenation from the abundant bud bank into
many annual shoot generations, leads to a complex shoot
age structure within ramets. The growth form of EB clones
is phalanx rather than guerrilla (Albert et al. 2004), imply-
ing that clones produce short internodes and closely packed
ramets, and to a lesser degree long internodes and widely
spaced ramets. Average ramet age is also affected by its
habitat, and increases with forest maturity in older stands
(Nielsen et al. 2007). Old forests have lower light influx,
which results in slower growing and older ramets. Most
ramets in a forest habitat are younger than 6 years old
(Flower-Ellis 1971; Nielsen et al. 2007), although 6-12
years is also common, and ramets of 34 years have also
been recorded (Flower-Ellis 1971). Shoots on single ramets
are a mix of fertile or vegetative shoots. Fertile shoots have
a lower dry weight increment than the vegetative shoots
(Tolvanen 1994), and alterations of vegetative and fertile
periods are present within single ramets (Paakonen et al.
1991). The newest part of the stem from the previous year
will be green, soft, and highly branched (Ritchie 1956).
An interesting investigation was undertaken in Belgium,
identifying 95 clones among 586 samples analyzed. Despite
of intra-population variability in the clonal diversity and in
spatial structure of the clones, no differences in clonal
diversity were detected between the three different studied
habitats. A high proportion of genetic variation existed
within populations (86%), while the variation was only 14%
between populations (Albert et al. 2004). For seedlings, the
primary rhizome does not appear until the third year at the
earliest (Sylven 1906). The present authors, however, found
that seedlings on farmland, improved by added natural peat,
grew rhizomes the second year, after seed germinating in
March and planting in July (Nestby pers. obs. 2009).
BUD DEVELOPMENT AND FLOWER INDUCTION
EB flowers are born singly (rarely in pairs) in the axils of
the leaves on one-year old twigs from May to June. The
twigs are sitting on aerial shots that are at least three years
old (Flower-Ellis 1971; Tirmenstein 1990; Featherstone
2002). However, sexual reproduction starts and peaks ear-
lier in rejuvenated shoots, indicating shortened ageing pro-
cess in these (Tolvanen 1994). Flower initials are developed
the year before flowering and overwinter in a dormant bud.
There are two types of buds; buds enclosing two bracts
and one single flower, and buds which bear a single lateral
shoot and a flower. These flowering shoots normally drop
together with the leaves in autumn. Some buds do not deve-
lop flowers and grow as vegetative short shoots (Flower-
Ellis 1971). With respect to floral structure, the stamens are
closed within the narrow corolla, while pistils stretch out of
the corolla. Flower diameter is approximately 4-6 mm
(Flower-Ellis 1971; Featherstone 2002). Following the pat-
tern of EB in a ten years period revealed that EB flowered
heavily every second year (Kardell and Eriksson 1990;
Selås 2000), indicating a biannual flowering pattern.
In the sweet lowbush blueberry the development is
similar. During late summer, floral bud development is ini-
tiated in the apical meristem of the upright shoot and then
proceeds down the axis of the stem in axillary buds located
in the leaf axils. However, in contradiction to the EB they
carry “clusters” or multiple inflorescences that originate
from a compound floral bud. Growers have been able to
dramatically increase yields of the sweet lowbush blueberry
by pruning the fields on alternate years. This ensures that
the fields are comprised of new shoots and thus have a high
flower density. Consequently clonal growth is likely to be
an important factor that constrains fruit and seed number
(Nuortila et al. 2002). A similar practice in EB could delay
the fruiting with several years since the generative part of
the tiller will be removed. It is a question if the shoots
sprouting from buds on the remaining long shoot initiate
flower buds the first autumn after cutting in the spring as an
effect of rejuvenation (Tolvanen 1993). Cutting may delay
sexual reproduction because of increased allocation of re-
sources to vegetative growth to replace lost tissue (Sones-
son and Callaghan 1991), and it is suggested that new EB
ramets do not produce flowers until two or three years after
cutting (Tolvanen et al. 1993a, 1993b). The effect of cutting
is under investigation by the present authors (Nestby et al.
pers. comm. 2008).
POLLINATION AND FRUIT DEVELOPMENT
As a result of the extent of large EB clones, the rate of sel-
fing through geitonogamy (transfer of pollen between
flowers of the same genet) is significant (Albert et al. 2008).
In northern boreal forests EB is obligately insect pollinated,
and the main pollinators (bumblebee queens) make approxi-
mately 76 (Nuortila et al. 2002) to 90% (Albert et al. 2008)
of their flights within a distance of only 40 cm. The EB
have no mechanisms for avoiding self-pollination or self-
fertilization (Nuortila 2007). Flowers have been found to set
fruit equally well with self-pollen and cross-pollen (Nuor-
tila et al. 2002; Raspé et al. 2004), but cross-pollinated
flowers matured more seeds and aborted fewer seeds than
those that were self-pollinated. Approximately four times as
many seeds in cross-pollination were set at 10 m distance
when compared to self-pollinated flowers, suggesting pol-
len limitation (Jacquemart 1997) and an inbreeding depres-
sion at the seed stage (Fröborg 1996; Raspe et al. 2004;
Nourtila et al. 2006; Nuortila 2007). It appears to be a clo-
nal variation in self-fertility (Raspe et al. 2004; Nuortila
2007). Berry fresh weight is positively related with the total
weight of seeds and the number of seeds (Ranwala 2001;
Ranwala and Naylor 2004), meaning that fruit yield would
benefit from cross-pollination. Subsequently, for successful
fertilization to occur, extensive interphenotype (clone) pol-
len movement is required in fields. This indicates that for
Fig. 2 Vaccinium myrtillus. The coin is 21 mm in diameter. (Nestby
2009).
8

European blueberry domestication. Nestby et al.
cultivation purposes, it could be useful to expand the “win-
dows of opportunity” by in situ rhizomes or seeds or by
planting seedlings or advanced clones, to increase the repro-
ductive success and clonal diversity within pollinator flight
distances.
FRUIT CHARACTERISTICS
The most significant characteristic of blueberries is their
high content of beneficial nutrients and bioactive phytoche-
micals (Table 2). Nutritional compounds comprise carbo-
hydrates and organic acids, which mainly contribute to the
taste impression, accompanied by aroma volatiles. The
favourable berry aroma from EB shows complex phytoche-
mical patterns based on more than 100 compounds (Rohloff
et al. 2009), compared to V. corymbosum (Parliment and
Kolor 1975; Hirvi and Honkanen 1983) and V. ashei (Hor-
vat et al. 1996).
The nutraceutical quality is recognized by the abun-
dance of natural antioxidants such as proanthocyanidines
and anthocyanins (Faria et al. 2005) together with the oc-
currence of other potent flavonoids (Cho et al. 2005), other
phenols (Taruscio et al. 2004; Zadernowski et al. 2005), and
reasonable amounts of ascorbic acid (Stewart 2004). An
obvious difference is the blackish fruit flesh colour of EB
compared with the whitish colour of the American blue-
berries, including V. angustifolium, V. corymbosum L. (high-
bush), V. ashei Reade (rabbiteye) and V. myrtilloides Michx.
(sourtop lowbush). Jam made of EB has a more pronounced
blueberry-flavour and odour than that of e.g. the V. co r y m -
bosum cvs. ‘Bluecrop’ and ‘Berkely’ (Rødbotten et al.
2005). The berries of EB are characterized by 15 anthocya-
nins according to a Finnish study (Lätti et al. 2008). A sig-
nificantly lower content of the total anthocyanins was ob-
served in berries of the southern regions of Finland com-
pared with the central and northern regions, which is in
accordance with observations on latitudinal variation in
Norway (Nestby et al. 2010, unpublished). Differences in
the proportion of anthocyanins were also reported (Lätti et
al. 2008). In general, berries from EB are characterized by
higher levels of total anthocyanins, phenols, and antioxi-
dants, whereas highbush varieties show superior berry
weight and thus yield potential (Tab l e 2). The study of
berry peels and flesh with regard to the in planta distribu-
tion of bioactive phytochemicals, emphasizes the health-
beneficial properties of EB compared to highbush blue-
berries (Riihinen et al. 2008). Recently, resveratrol and
structure-relative compounds that have been reported to
show cancer-chemopreventive activities, have been des-
cribed in Vaccinium berries (Rimando et al. 2004). Ad-
ditionally, EB seed oils have been shown to serve as an
excellent source for linolenic acid, essential fatty acids,
tocopherols and carotenoids (Parry et al. 2005).
In order to fully address fruit characteristics, not only
the internal quality but also external parameters based on
morphological and physiological traits have to be con-
sidered. Blueberries from high- and lowbush cultivars show
an extended shelf-life and can be freshly stored for periods
from 4 to 6 weeks (Krupa and Tomala 2007; Echeverría et
al. 2009) when using controlled (CA) or modified atmos-
phere (MA) conditions. Due to their flesh firmness and
berry skin properties, they are fitted for long-distance trans-
port for sale on external markets far from the production
site. In contrast, berries from EB show a relatively higher
degree of vacuolization at full maturation stage, which
makes them more suitable for distribution on local markets
and fresh consumption rather than long-term storage and/or
transport. However, high levels of antimicrobial and bioac-
tive compounds in EB have high potential to suppress bac-
terial and fungal growth (Koskimaki et al. 2009). Posthar-
vest quality of blueberries is clearly reduced due to water
loss, lower firmness and shrivelling, as illustrated with V.
ashei (Schotsmans et al. 2007) and V. corymbosum (Krupa
and Tomala 2007). Whereas levels of anthocyanins and anti-
oxidant capacity decrease over time, the taste parameters of
soluble solids and titratable acidity often remain unchanged
also after several weeks of storage (Krupa and Tomala
2007). Frozen storage of blueberries as an alternative for
quality preservation of whole berries, does not significantly
change nutrient and anthocyanin composition even after 4
months (Poiana et al. 2008), when suitable freezing condi-
tions are applied.
POTENTIAL OF ENHANCING PLANT
DEVELOPMENT AND FRUIT YIELD BY
MANAGEMENT
Half cultivation
In Finland, forest owner preferences have changed from an
economy based on tree value only, to an evaluation where
also berry yields and other non-wood products have to be
taken into consideration. This has resulted in the need to
assess the effect of silvicultural treatment on berry yields
Tab le 2 Chemical composition of V. myrtillus, and other selected Vaccinium species.
Quality parameter V. myrtillus
Norway1
V. myrtillus
references2
V. corymbosum
references3
V. angustifolium
references4
Berry weight (mg f.w.) 457 r 81 328 r 63 1635 r 346 326 r 67
Dry matter (g/ 100 g f.w.) 15.0 r 1.6 15.2 r 3.2 16.4 r 4.1 22.1 r 13.1
Soluble solids content (Brix value in %) 10.8 r 1.6 9.8 r 1.1 12.7 r 2.1 15.4 r 1.6
pH 2.7 r 0.1 3.1 r 0.1 3.2 r 0.2 2.7 r 0.1
Titratable acidity (g/ 100 g f.w.) 1.4 r 0.2 2.4 r 1.5 1.4 r 0.6 0.9 r 0.1
Total anthocyanins (mg/ 100 g f.w.) 275 r 72 364 r 189 145 r 54 181 r 152
Total phenols (mg GAE/ 100 g f.w.) 612 r 75 472 r 164 289 r 105 546 r 255
Antioxidants FRAP (mmol/ 100 g f.w.) 5.7 r 1.2 5.3 r 2.2 2.6 r 1.1 9.8
Fructose (mg/ 100 g f.w.) 5290 r 1027 3687 r 1092 6171 r 3150 3900
Glucose (mg/ 100 g f.w.) 5348 r 1074 3380 r 988 3296 r 852 5150
Sucrose (mg/ 100 g f.w.) 578 r 270 411 r 187 180
Citric acid (mg/ 100 g f.w.) 1321 r 150 683 r 171 427 r 168
Malic acid (mg/ 100 g f.w.) 298 r 95 261 r 195
Quinic acid (mg/ 100 g f.w.) 1703 r 476 1370 46 r 73
Catechins (mg/ 100 g f.w.) 45 r 24 5.0 5.3 r
Chlorogenic acid (mg/ 100 g f.w.) 32 r 18 59 r 82
Ascorbic acid (mg/ 100 g f.w.) 3.0 r 2.5 18.6 r 24.6 9.2 r 3.8 12.1 r 6.9
Gallic acid (μg/ 100 g f.w.) 834 r 235 1760
Quercetin (μg/ 100 g f.w.) 473 r 262 2263 r 966 3824 r 2764
1Based on experimental data from Norwegian trials in 2009 (Nestby et al., unpublished data)
2Data compiled from 27 references
3Data compiled from 24 references
4Data compiled from 4 references
9

The European Journal of Plant Science and Biotechnology 5 (Special Issue 1), 5-16 ©2011 Global Science Books
(Kangas 1998). In Norway, this attitude has not been very
apparent. However, there has been a recent and substantial
interest in the economical value of resources other than
trees in outlying fields. Unfortunately, this has mainly foc-
used on fishing, hunting and tourism. The blueberry resour-
ces have been largely overlooked, but should be evaluated
as important. Some ecological investigations of forest man-
agement including EB, could give inputs to how this re-
source could be made more easily available for exploitation.
In addition to forest management, climate, soil conditions,
insects and diseases, browsing animals etc. have an influ-
ence on the development of the European blueberry.
Forest cutting
The EB is severely affected by clear-cutting with substantial
reductions in vegetative growth, shoot survival, ground
cover and fruit production, and an increase in shoot phenol
content. This was confirmed in a study by Atlegrim and
Sjöberg (1996) who reported a reduced ground cover and a
more patchy spatial distribution after selective cutting.
Interestingly, the vegetative investment and shoot survival
after cutting did not differ from zero cutting (Atlegrim and
Sjöberg 1996). This suggests that percentage cover of EB is
highest in established old forest. A study on different age
classes of V. myrtillus in Polish pine stands strengthen this
theory. It was shown that percentage cover- area and weight
of aerial shots were highest in 40-80 years old stands
(Kalinowski 2004). Similarly, in a pine forest of Kola, 200
years old stands of V. myrtillus had the highest production
and vitality (Maznaya 2001). This is in agreement with Kar-
dell and Eriksson (1995), who found that percentage cover
of EB increased with forest maturity, and that clear cutting
reduced percentage cover with 80%, and that the recovering
was very slow.
There is suggested a negative connection between EB
cover and irradiance; the cover was poorest at clear cutting
and greatest at intermediate irradiance, which coincided
with high crown forest stands (Parlane et al. 2006) and for-
est regularly thinned (Kardell and Eriksson 1995). However,
under Norwegian conditions the effect of clear cutting was
the opposite, and the average performance of EB decreased
with increased forest maturity and larger tree biomass. This
experience could be caused by the use of relatively small
clear cuts in Norwegian forests (Tolvanen 1994; Nielsen et
al. 2007).
Climate
Besides forest management, climate has a decisive impact
on the development of the EB. Vaccinium grow wild in the
temperate zone and stretches into the arctic climatic zone.
This environment has typical changes in seasons with rela-
tively warm summers and long days followed by colder
autumns and winters with abundant and persistent snowfall
and short days. These changes have made it necessary for
the blueberry to stop growth in late autumn, to avoid re-
sumption of growth too early in the spring, and to develop
avoidance (snow cover) and tolerance to low temperature
stress (Rowland et al. 2004). This implies that moving types
of EB from northern areas to southern areas or vice versa
probably will be unsuccessful.
In the last decades the winters have generally been mil-
der and the snow cover more unstable, at least at low alti-
tudes in Scandinavia. The importance of snow cover was
notified by Gjærevoll (1949), giving that snow cover is an
important factor which determines the altitudinal distribu-
tion of EB. In the absence of a protective layer of snow,
plants are vulnerable to cold winter temperatures and may
be killed (Hall et al. 1971), though it is moderately buffered
against frost in late winter and early spring (Tolvanen et al.
1997). In a winter five degree warmer than average in NE
Sweden during 1991-1992, V. myrtillus suffered lethal inju-
ries. It was suggested that this was connected to a conside-
rable decrease in solute content during winter (Ögren 1996).
Closer examinations including experiments with infrared
heating lamps run with or without soil warming cables,
confirmed the effects of winter warming. After a simulated
one week long extreme winter warming event in early
March, Vaccinium myrtillus had delayed bud development
by up to 3 weeks in the following spring (June) and reduced
flower production by more than 80% (Bokhorst et al. 2008).
Later this was more carefully scrutinized and tissue
water in the shoots was observed in winter compared with
spring and early summer. Soluble solids tended to decrease
from December to February under snow cover, while re-
maining constant under artificial gray and transparent cover
(roofing), indicating an enhanced demand for synthesis of
proteins, including dehydrins that protect against drought
(and freezing) under conditions without snow cover. Also
increases of metabolism in early spring were less or absent
in plants that wintered without a snow cover. This can be
explained by a delayed activation of metabolism resulting
from multiple stresses (LT, drought, light) that acted simul-
taneously on the EB plant (Tahkokorpi et al. 2007). How-
ever, it should be noticed that blueberries have dormancy
mechanisms that are present and functional during the win-
ter. The lowbush blueberry need temperatures of less than
4°C for 1600 hours for dormancy to be broken, which in
Nova Scotia typically occurs in February (Percival 2010
pers. obs.). Lack of chilling could give reduced bud burst
mistaken as winter injury. Also, nutrition would influence
winter hardiness, and Taulavuori et al. (1997) concluded
that winter hardening and glutathione status in the EB seems
to be sensitive to nitrogen fertilization, and not affected by
elevated CO2 and O3.
In a domestication strategy breeding EB-clones for win-
ter hardiness could be an objective. Little is known of in-
heritance of this character. In highbush blueberries, cold
hardiness is controlled largely by additive, multiple and
largely dominant gene effects. These genes are dehydrins
(bbdhnd1-bbdhn5) (Arora et al. 2000; Rowland et al. 2004).
Though it is not examined, probably similar mechanisms
are prevalent in the EB. However it may be anticipated that
the genes that regulate hardiness at least to some degree are
different from those found in highbush blueberries.
Another aspect worth noting is the vulnerability of
flowers to be injured by frost in late spring/early summer.
This has happened more frequently the last decades in both
lowbush and EB due to milder winters and earlier resump-
tion of growth in the spring. This frost injury can be as rate
limiting as winter injury, and changes with the developmen-
tal stage of the plant. The pattern observed in a ten year
period that EB flowered heavily every second year, could
partly be a result of this, but also due to the physiological
effects associated with biennial bearing. During registra-
tions over three years in central Finland, fruit yield varied
from zero to 130 kg ha-1, and in a Swedish 15 year study,
yields varied from 0 to 450 kg ha-1 depending on site and
year. The years with almost zero yields always had a history
of frost during bloom (Kardell and Eriksson 1990, 1995).
An examination in the Arkangels region of Russia illus-
trated that profuse flowering during fairly warm weather
with rain showers after the late spring frost (mid-June), and
enough moisture in July and August, secured high fruit
yields. These conditions typically occurred every fourth
year. In a typical good year the yield averaged from 171 to
341 kg ha-1 (Puchnina 1996).
Plant reactions that can reduce LT injury were observed
in cranberry uprights (V. macrocarpum Ait.) and fruit.
Work ma ster et al. (1999) suggested that ice nucleation of
leaves performed by ice penetration via stomata located on
the abaxial surface, and that the thick cuticle present on the
adaxial surface was an effective barrier to intrinsic nuclea-
tion. Only frozen moisture at the calyx end of the fruit in
the remnant nectary could induce fruits to freeze, most
likely through stomata. If a similar appearance is present in
EB it would be a valuable trait preserving the fruit quality
by supercooling in short periods with warm freezing tempe-
ratures in the autumn.
10

European blueberry domestication. Nestby et al.
Soil and nutrition
The EB is one of the dominating dwarf shrubs in forest
habitats with low nutrient availability due to its clonal
growth habit, the symbiosis with ericoid mycorrhiza (Bon-
fante-Fasolo et al 1981; Kasurinen and Holopainen 2001)
and the ability to take up organic nitrogen (Näsholm et al.
1998).
The optimal conditions for EB growth, development
and fruit yield, according to Svalestad (1983), occurred in
Norway under conditions of high humidity and minimal
shade. In addition he found that mineral nutrition increased
the fruit yield at sites where the EB was a dominating spe-
cies, especially when water was sufficient.
Similarly, in other studies, mineral nutrition was an im-
portant factor for plant productivity. In the northern Apen-
nines, total community net primary production (NPP) of
three communities was closely related to nutrient availabi-
lity. NPP of V. myrtillus peaked in the most fertile habitat,
and within this the N to P ratio in the whole plant as well as
in the leaves reflected the soil phosphate concentration with
foliar N to P ratios of less than 16 in the poorer sites. The
responses showed by other species in the same habitat sug-
gest that the response of EB is individualistic in response to
the nutrient availability, and that the growth is P-limited
(Gerdol 2005). A study of Kardell and Eriksson (1995) over
15 years showed that fertilization with 150 kg ha-1 of am-
monium nitrate the second year after establishment of trial
plots, and again before the 10th year, gave varying reactions
between field trials situated in the south and north of Swe-
den. Generally, however, fruit yield increased the first years
after implementation of fertilizer, but was reduced gradually
towards the second application of fertilizer. After the second
application a new increase in fruit yield occurred followed
again by a slow decline, but not as significant as after the
first application. The best results were achieved when ferti-
lization and thinning of trees were combined.
On the contrary to the above mentioned studies Nordin
et al. (2006) reported no effect on growth of EB after fertili-
zing a boreal forest under storey vegetation with am-
monium and nitrate in the range 12.5 to 50.0 kg N ha-1.
The uptake of nutrients in Vaccinium is facilitated by
symbioses with ericoid mycorrhiza, which provide the hosts
with access to soil-nutrient resources that would otherwise
be largely unavailable to the plant (Read 1980). Mycor-
rhizal formation is also contributing to the success of EB in
nutrient stressed environments, and Bonfante-Fasolo et al.
(1981) found that nearly all root hairs examined were mycor-
rhizal, although infection intensities varied at different
times of the year. A heavy fungal infection takes place with-
in new root formation in late summer and autumn, decrease
during winter and increase gradually again towards late
summer. The mycorrhizal colonization of Vaccinium roots
take place in the cortical cells where the fungi differentiate
typical intracellular hyphae coils, which characterize the
symbiotic association between ericaceous plants and their
symbions (Harley Smith 1983; Jeliazkova and Percival
2003a, 2003b).
In a forest several factors influence nutrient availability
of the EB. At clear-cut it is important to prevent leaching
and surface erosion of nutrients through the presence of
vegetation that retains nutrients in the ecosystem. In a
mixed forest dominated by Norway spruce (Picea abies L.)
in eastern Finland, the biomass of EB significantly de-
creased after clear cutting. However, it remained a marked
nutrient sink, and the biomass returned to initial levels soon
after clear cutting as did the nutrient contents of ground
vegetation (Palvainen et al. 2005). The fast recovery of V.
myrtillus in this study is in contradiction to the findings of
Kardell and Eriksson (1995) in a 15 years study, who found
that V. vitis-idaea had a better recovery than V. myrtillus.
The uptake of nutrients is also dependent on soil pH,
and it is shown that there is an effect on pH of type of domi-
nating tree species on blueberry land. Soil pH was higher
under birch (4.7) than under spruce (4.1), while the C/N
ratio was lower under birch (17) than under spruce (23), in
a podzol and humus type moor soil. Microbial biomass, C
and N, net N mineralization and net nitrification were all
higher under birch than under spruce, per unit organic mat-
ter (Smolander et al. 2005).
Insects
An injury of an insect may be affected by interactions of
other factors in the environment. By example the ‘Winter
moth’ larvae (Operophtera brumata, Lepidoptera) may feed
heavily on EB. At the individual level, altered food plant
quality due to repeated infection by the fungus Va ld e n si a
heterodoxa, had no effect of the larval performance in labo-
ratory experiments, but both survival to the adult stage and
adult weight were positively affected by N fertilization. In
addition exclusion of insectivorous birds increased the fre-
quency of larval damage to EB shoots, indicating higher
larval densities, and there was an indication of higher bird
predation in fertilized plants. The results suggest that top-
down effects (in this case birds) are more important for lar-
val densities than bottom-up effects (e.g. nitrogen, fungus),
and that bird predation may play an important role in popu-
lation regulation of ‘Winter moth’ in boreal forests (Streng-
bom et al. 2005). Also Agriopsis aurantiaria feed on the
leaves of EB in the lowland south in Norway. ‘Autumnal
moth’ (Epirrita autumnata) and ‘Winter moth’ are often
found together, and both may occasionally de-leaf the birch
(Betula pubescens Ehrh.) and EB totally (Fjelddalen 2009;
Wikipedia 2009b).
It is shown that the wood ant (Formica aquiloni) is
beneficial for the EB. Close to ant nests herbivore damage
to the EB was reduced and proportion of flowers succeed-
ing to berries was increased. It was therefore suggested that
distance to wood ant nests and thereby reduced predation
from ants, affect herbivore damage to the EB and its repro-
ductive success. However, vegetative growth and reproduc-
tive investment was not affected by distance to ant nests,
indicating that the EB can also compensate for losses due to
herbivore injury (Atlegrim, 2005). It should however be
noted that the red ant may feed on the blueberry flower.
This was observed in Norway. However, it seem like the in-
jury is mainly on the corolla and not on the pistil or unripe
fruit, since the berries developed normally (Nestby 2008
pers. obs.).
This suggests that when methods to improve the yield
of the EB are implemented it should be strongly considered
not to override the natural defence mechanisms, but rather
try to strengthen these or at least not weaken them.
Diseases
Leaf damage caused by diseases is often observed in EB
fields. The most common is Valdensia heterodoxa. The
interaction between this parasitic fungus and its host plant
the EB, was affected by nitrogen additions over 5 years in a
boreal forest in northern Sweden. Disease incidence on
leaves increased following N addition and the effect was
stronger in large than in small plots (ranging 1 to 5000 m2),
and disease incidence was also positively correlated with
precipitation. High summer precipitation enhanced the N
effect, suggesting that precipitation may modify the effects
of N deposition on plant-parasite interactions. Parallel to
this it is observed in lowbush fields of Nova Scotia that N
increases canopy biomass, this lengthens canopy wetness
duration and greatly increases the likelihood of infection
(Percival 2010 Pers. comm.). This may complicate predic-
tions of future effects of N deposition as precipitation pat-
terns are expected to change as a result of climate change.
The results suggests that small scale fertilization experi-
ments may underestimate future large-scale effects of N-
deposition, and indicate the need for increased awareness of
the problems (Strengbom et al. 2006). N-induced changes
in the constitutive levels of soluble conjugated amines did
not seem to explain the increased parasite (Valdensia hete-
11

The European Journal of Plant Science and Biotechnology 5 (Special Issue 1), 5-16 ©2011 Global Science Books
rodoxa) susceptibility of the EB under N enrichment. Gene-
rally, the concentration of free diamines and insoluble con-
jugated putrescine were higher in diseased than in healthy
shoots, suggesting parasite-induced accumulation of dia-
mines. Free spermine seemed to accumulate in unfertilized,
diseased plants, but in fertilized plants this induction was
dampened, suggesting that N-induced alterations in sper-
mine metabolism may promote the spread of parasites on
the EB under N-enrichment (Witzell et al. 2005).
Mummy berry disease (Monilia vaccinii-corymbosi) is
one of the most important plant pathogenic fungi on blue-
berries in America and the first verified detection in Europe
(Austria) was in 2002. The fungus was likely introduced to
Europe years ago and is present in other blueberry plantings,
but has not been identified due to possible unfavourable
weather conditions (like low temperature) for the fungus or
confusion with similar fungi (e.g. Botrytis cinerea). It re-
mains to be seen how this disease will affect the EB, which
has some resistance to this pathogen (Gosch 2006).
Weeds
Weed pressures are different in established old forests com-
pared with a clear cut sites. These pressures are also more
prevalent under birch (Betula pubescens) because of dif-
ferences in light penetration to the ground, than under Nor-
way spruce (Picea abies). Birch impose cascading effects
on both above- and below-ground communities, soil chemi-
cal and physical properties and ecosystem processes. Com-
pared with heather (Calluna vulgaris) plant species richness
decreased and the vegetation composition changed under
birch, with lower cover of grasses and EB (Mitchell et al.
2007).
When using applications of N fertilizer in EB, problems
could be encountered as a result of heather responding posi-
tively to N-application (Britton and Fisher 2008). Similar
effects were observed in clear cut areas of Norway spruce
forest during 2009, with ‘wavy hairgrass’ [Deschampsia fle-
xuosa (L.) Trin.] and ‘fireweed’ (Epilobium angustifolium)
competing strongly with the EB (Nestby 2009 pers. obs.).
Also ‘Birch’ (Betula pubescens) sprouting from stubs and
‘European Rowan’ (Sorbus aucuparia) may be a problem if
caution is not taken to prevent these to develop (Nestby
2009 pers. obs.).
Browsing animals and birds feeding on the berries
Moose (Alces alces) and deer (different species), which are
quite abundant in Norway, are feeding on EB plants (Fea-
therstone 2009). This was confirmed in an examination
undertaken in a mature Scandinavian pine (Pinus sylvestris)
forest. At sites subjected to differing natural intensities of
grazing by Cervus elaphus (red deer), it was shown that
ramet size, abundance and fruit set and invertebrate activity
on EB were negatively related to grazing intensity. Even at
low grazing intensities the performance of the plant was
affected. The effect on fruit production and invertebrate
activity indicated that red deer grazing has a negative im-
pact on the population dynamics of the plant (Tømmervik et
al. 2004; Hegland et al. 2005; Melis et al. 2006; Parlane et
al. 2006). The EB have a protective mechanism against
heavy feeding of bank vole (Clethrionomys glareolus), pos-
sibly explained by changes in plant chemistry (Selås 2006).
These browsing effects are also confirmed in studies simu-
lating herbivory (Tolvanen et al. 1993b; Tolvanen 1994).
EB foliage is highly palatable and it is also an important
food source for birds such as red grouse (Lagopus lagopus),
ptarmigan (Lagopus mutus) and black grouse (Tetrao tetrix).
The capercaillie (Tetrao urogallus) in particular depends on
EB, and it eats the stems and buds in winter, as well as the
leaves in spring and summer (Featherstone 2009). It is well
known in Scandinavia that ‘Gray thrush’ (Turdus pilaris)
and ‘Starling’ (Sturnus vulgaris) feed on the fruit (Nestby
2009 pers. obs.). Therefore, if the intention is to increase the
EB abundance, it may also be important to reduce or some-
how deter the number of browsing animals (Tømmervik et
al. 2004; Hegland et al. 2005; Melis et al. 2006; Parlane et
al. 2006).
Finally, examinations have shown that EB respond nega-
tively in growth performance and age to the disturbance and
stress on ski pistes (Rixen et al. 2004).
Cultivation on farm land
The main difference from forest fields is that the soil pH
often will have to be adjusted by adding sulphur or organic
matter of low pH (e.g. compost, natural peat). Also it may
be necessary to top-dress the soil with a layer of organic
matter at specified intervals. In addition the weed pressure
may be different from forest fields, and the protection
against light-related stress and wind given by forest trees,
will normally be lacking. However, when moving the EB
into cultivated land the possibility to adapt the cultivation
system to the plant will be more flexible. There is very little
experience with this kind of cultivation, and it is necessary
to take a broad and sequential experimental approach to
build a knowledge base.
REPRODUCTION
Seeds
The reproduction of EB has been widely studied due to the
use of EB for re-vegetation purposes and for its significance
in forest and heath ecology, where EB is one of the
dominating dwarf shrubs. The natural reproductive success
of EB in forest ecosystems is contributed to it being a spe-
cies with a long life span, a mixed breeding system and a
high seed dispersal potential (Flower-Ellis 1971). However,
the importance of seeds in regeneration of EB seems to
fluctuate. EB has been found to be one of two dominant
seed-bank species in five boreal forests stands in northern
Sweden (Granström 1982). On the contrary moors in Scot-
land (Ranwala and Naylor 2004) and in a closed temperate
forest of Spain (Laskurain 2004) had a complete absence of
seeds or seedlings. Interestingly, EB was one of the most
frequent shrub species in all these sites, resulting in its
clonal growth with subterranean rhizomes being essential
for spreading. Local patches of EB have been found to have
a shoot density up to 400 reproductive shoots per square
meter (Ranwala 2001). Consequently, seedling recruitment
in natural populations is possible within stands of estab-
lished conspecific adults only at “windows of opportunity”
(Erikson and Fröborg 1996). “Recruitment at windows of
opportunity” (RWO) is likely in EB since substrates suita-
ble for germination, seedling survivorship and juvenile
growth occur within the habitat space already occupied by
conspecific adults. This strategy provides that seed availa-
bility is not limiting, contributing to explain why EB each
year produce copious numbers of seeds and at the same
time is characterized by an almost total absence of seedlings.
RWO may also explain the incidence of genotypic diverse
clones represented by only one ramet that may exist within
spatially large clones (Albert et al. 2004).
The number of seeds per fruit reported in literature for
EB fruits range from an average of 25 (Flower-Ellis 1971)
to 40 (Ritchie 1956) to 71 (Ranwala and Naylor 2004). Seed
number varies greatly in response to pollination treatment
with cross-pollinated berries containing a maximum of 120
mature seeds, while self-pollinated berries containing a
maximum of 35 (Nuortila et al. 2006). Upon examining the
seeds at berry maturity, the average number of mature seeds
per berry was 66 and 12 in cross- and self-pollinated berries
respectively.
Seed germination occurs over the range 15-24°C (Ran-
wala and Naylor 2004), and has been shown to occur when
stratified in the presence of light under cool (15.5°C) tem-
peratures for more than 12 weeks (Baskin et al. 2000). The
best germination has been obtained by no stratification and
16 weeks of incubation in 12 h light at 25/15°C day/night
12

European blueberry domestication. Nestby et al.
temperatures (Baskin et al. 2000). EB seeds are probably
conditionally dormant at maturity, as the maximum possible
germination percentage was not obtained using fresh seeds
(Baskin et al. 2000). Trials have also shown that germina-
tion is poorer in light having a high far-red ratio, as is under
a dense tree canopy (Skrindo 2005). Digestion of berries by
birds also affected EB seed germination (Honkavaara et al.
2007), while digestion by bears did not enhance germina-
tion (Skrindo 2005).
There is a considerable variation in EB fruit and hence
seed production between years. Depressed berry production
has been associated with high temperatures during flower-
bud formation in autumn, high temperatures in winter in
association with thin snow cover, frost during flowering in
spring and low or high amounts of precipitation during
berry ripening in summer (Selås 2000). Analyses of a 50-
year time series of fruit production in EB showed that the
highest production occurred in years with relatively high
levels of summer precipitation.
It is suggested that an average temperature increase will
reduce seed viability and cause negative implications for
the spread of EB in Scotland (Ranwala and Naylor 2004),
while it is likely to benefit from a warmer climate in the
subarctic (Milbau et al. 2009).
Vegetative propagation
While vegetative regeneration by rhizomes is very success-
ful in nature, vegetative propagation for making homoge-
nous plant material for cultivation and research purposes
has a low success-rate (Jaakola et al. 2001). The EB may be
propagated both in vivo and in vitro and different media
have been used. Investigating growth initiation in vitro in
EB using different concentrations of N6-isopentenyladenine
in the modified MS-medium, Jaakola et al. (2001) found
that the optimal concentration for the initiation of growth of
microshoots in vitro was 49.2 μM, compared to 24.6 and
78.4 μM. The treatment undertaken in spring, resulted in
44% growing explants after 8 weeks. Rooting of the EB
microshoots ex vitro were improved by incubating them in a
2.07 mM solution of a potassium salt of indole-3-butyric
acid (KIBA) at a concentration of 0.49 μM for 5 minutes
before planting in peat. Then 71.9% of the microshoots
rooted after 5 weeks, while 81.3% rooted in vitro in a root-
ing medium containing IBA at 0.49 μM.
Our own experiments in cooperation with University of
Natural Resources and Applied Life Science, Institute of ap-
plied Microbiology in Vienna Austria, with in vitro estab-
lishment and multiplication, have shown that clones of V.
myrtillus are successfully established and multiply with a
rate of 3-4 shoots per subculture (Laimer pers. comm. 2010).
Micropropagated plants have been shown to have a preco-
cious and higher rhizome production compared with plants
propagated from cuttings in both lingonberry (V. vitis-idaea)
(Gustavsson and Stanys 2000; Debnath 2005) and lowbush
blueberry (V. angustifolium) (Morrison et al. 2000). Rhi-
zome production in lowbush blueberry is also affected by
the N status (Smagula and Hepler 1980).
Micropropagation is reliable and efficient, especially for
the rapid introduction of new cultivars, and large-scale
liquid cultures combined with automated bioreactors could
be a tool to eliminate most manual handling in micropropa-
gation and reduce production costs significantly. Addition-
ally, molecular markers introduced in Vaccinium are power-
ful tools in the genetic identification of clonal fidelity (Deb-
nath 2009). A combination of advanced micropropagation,
including molecular markers, could be valuable in a future
establishment of new large plantings of EB on abandoned
farm land. However, experiences from the Canadian low-
bush industry have shown that the success of advanced cul-
tivars has been limited (Jamieson pers. comm. 2007.). The
reason is more political than horticultural, since the produc-
tion is advertised as exploiting the wild lowbush blueberry
growing in half cultivated fields. Anyway, in the effort to
domesticate the EB these tools should be integrated in a
scientific approach to the objective.
HARVEST AND DELIVERY
It would be a benefit to have a model for prediction of fruit
yield. It would provide information to decide fruit retention
and harvestability, and if this could be provided to end users
prior to harvest, it would assist in determining estimated
berry supply. In Finland Pukkula (1988) created a model
collecting data on site properties, trees and berry yields.
However, this model was dependent of a large number of
empirical data over many years and therefore, was easily
biased. Models based on expert modelling (Muhonen 1995;
Ihalainen et al. 2002, 2003, 2005) and on regression analy-
sis, to relate the expert priorities to stand characteristics,
seem to be more appropriate. However, according to Kan-
gas and Mononen (1997) expert models can only relieve the
acute need for prediction models and produce temporary
models for forest planning inexpensively and quickly. To
construct models that reliably describe the effect of trees
and the site on berry yield, one needs to gather large quan-
tities of empirical data over several years (Belonogova and
Kuchko 1979). Recently Miina et al. (2009) have construc-
ted generalized linear mixed model techniques predicting
yields as a function of site and stand characteristics, using
the permanent sample plots of the National Forest Inventory
(Finland).
The predictions of the expert based models correlated
logically with site and stand characteristics and were in line
with earlier models based on empiric data, and were less
laborious. According to the model, yield would be posi-
tively correlated to tree age and height and the standing vol-
ume of pine. Conversely, the yield would be negatively cor-
related to the stand (tree) basal area, the standing volume of
deciduous trees and to a Vaccinium site type or poorer
(ecological term that defines the combination of tree species
and dominating shrub species). These Finish examinations
also show that forest stands of medium fertility, but also on
rather poor mineral soil, produce the highest EB yield in
different parts of Finland. However, these findings are not
unique probably because they are subjective, and it may be
difficult to distinguish between rather poor and medium soil
sites. In addition EB thrives on poorer soil sites in northern
Finland than in southern Finland (Ihalainen et al. 2005). In
Norway it is observed that blueberry yields may be quite
high at high altitudes or in the north where birch is domi-
nant forest forming tree species, or above the tree limit
(Nestby pers. obs. 2007). This coincide the defined ‘Blue-
berry birch forest’ in Norway which is dominated by EB in
the undercover (Bendiksen et al. 2008). A long-term study
conducted in the Kirov Region of Russia showed that ave-
rage daily air temperatures and quantity of precipitation
during spring-summer had the greatest influence on EB fer-
tility. Average long-term yield of EB was highest in the
spruce EB forest (41.5 ± 4.1 g m-2) and lowest in the aspen
EB forest (21.5 ± 2.6 g m-2).
Also the fruit picking technique can affect the yield, and
picking EB fruits with a comb once or twice a year de-
creased the number of plants growing. In all picking vari-
ants including hand picking once and twice a year, mass and
area of leaves were smaller than at no picking. However,
picking twice a year with a comb increased the reproduction
value compared with no harvesting (Kalinowski 2007).
CONCLUSION
Hence, the results and observations referred to in this paper
suggest that in situations of nutrient poor environments,
blueberry growth and development is reliant upon the
mycorrhizal association for nutrient availability. However,
given the need to provide sufficient upright stem growth for
adequate floral bud induction, initiation and development,
low applications of at least nitrogen and phosphorous may
be beneficial on the poorest soils. Also, adequate amounts
of water during growth and generic development are of
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The European Journal of Plant Science and Biotechnology 5 (Special Issue 1), 5-16 ©2011 Global Science Books
great importance to achieve a good fruit yield, as well as
avoidance of frost in the flower. For domestication of the
EB it will be of importance to consider the nutritional and
mycorrhizal conditions, and search optimal level of fertili-
zation and methods to strengthen the mycorrhizal associa-
tion dependent on soil conditions, to provide optimal yield,
fruit quality and plant health. A system where the ramet is
cut every second year, as practised in lowbush blueberry,
could contribute to increased fruit yield and effect the sec-
ond year pattern of EB flowering (biannual flowering), ob-
served by Kardell and Eriksson (1990), and positively con-
tribute to optimal shoot growth and flower bud production
in the sprout year. However, there are concerns that EB may
react differently, and that the regenerative shoots need more
years to develop fertile shoots.
It is indicated that medium or slightly poorer soil sites
will have the highest yield potential, and that a selective
cutting of trees is recommendable before clear cutting (at
least large clear cuttings), because that will prevent a mar-
ked reduction in EB phytomass production. Side effect is by
removing an extensive amount of forest there may be con-
cerns of removing carbon sinks and subsequently contrib.-
uting to greenhouse gas effect. There is presently no recom-
mendation on how EB and forestland can coexist for the EB
commercial production. The effects discussed above are
based on situations of stands with solely tree production,
where there are taken no steps towards weed control which
imply that all under vegetation are allowed to grow and
compete. By controlling the vegetation giving preference to
the blueberries, even richer soil sites could be suitable for
blueberry production if the soil pH was not too high (>5.2).
It is also a question how the mesomorphic character of the
EB can be handled. The EB thrives in shadowy conditions
and does not tolerate the desiccating impact of direct sun-
light (Raatikainen and Ratikainen 1983; Salo 1995). Also, it
is probably a matter of the EB undergoing excessive
amounts of photoinhibition (Percival 2010 pers. comm.).
Maybe it could be solved by cutting narrow stripes in the
forest instead of cutting a larger area leaving trees in a
spread pattern. This practice has been successfully used
with sweet lowbush blueberry production in Canada, and
should be examined in more detail with the EB. However,
in Norway growing on clear cuts show good results as well
as growing above the tree limit. This indicates that the
amount of light is not as much of a problem in EB as the
desiccative effect of sun and wind. If the water conditions
are sufficient, the EB should grow and produce well even
on large open areas. There is probably an optimal size of the
open spaces dependent e.g. on topography and altitude, also
because it is shown a reduced visit of pollinating insects
when the hedge effect of trees is lacking, and the average
temperature would also be reduced.
It is important to notice that EB is an important nutrient
sink after cutting and that the growth is markedly dependent
on P-level in the soils, which implies that the EB could
benefit from P-fertilization. However, other plant species
are effective nutrient sinks after forest clearing resulting in
the EB having to compete with these or use various technol-
ogies to minimize these grass and broadleaf weed pressures
in commercial production. An effective weed strategy also
would positively affect the fruit yield of the EB, as ob-
served in the sweet lowbush blueberry (V. angustifolium).
Other environmental factors including winter freezing, frost
during flowering, low temperatures and low rainfall during
flowering and growth and animal browsing have obviously
negative effect on fruit yields.
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