Beetroot (2004)
Stephen Nottingham
© Copyright: Stephen Nottingham 2004
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4. Cultivation
Cultivated
beets (Beta vulgaris) are biennials, although they are usually grown
as annuals. Beetroot produces green tops and a swollen taproot during its
first growing season. The nutrients stored in the taproot are used to produce
flowers and seeds in the second season. Cultivated beets thrive under a wide
range of conditions and are easy to cultivate. Beetroot is one of the most
popular vegetables grown on allotments and in gardens. It grows quickly, is
highly productive, and is usually free of pests and diseases. The cultivation
of beet is considered in this chapter, from sowing through harvest, to
storage and seed production. This chapter also looks at the conservation of Beta
biodiversity and how biotechnology is being used to modify Beta vulgaris.
The cultivated forms of Beta vulgaris must
be propagated from seed. The seed occurs in the form of a seed cluster,
glomerule or seedball. As noted in the previous chapter, botanically speaking
this is a fruit that typically contains two or three true seeds. Seedballs
(hereafter 'seeds') are sown directly into the ground, in the spring or
summer, when soil temperatures have risen above 7°C.
Deep digging is advised, to obtain a good tilth
for the first outdoor sowing in a garden. Around 7 g of seed is generally
considered sufficient for 10 m of row. Rows can be drawn with a hoe on a
finely raked seedbed. The seeds are big enough to be handled individually. In
gardens situations, they can be thinly scattered along the rows or placed
about 2 to 5 cm apart in the rows. Beetroot seed is sown at a depth of 1 to 3
cm, depending on cultivar. The seed of early sowings can be sown shallower
and denser than later sowings, where later sowings are to produce larger
beets for storage.
Rows or drills are typically spaced 25 to 45 cm
apart. In gardens, for minibeets or where beets are to be harvested very
small, rows can be spaced as little as 15 cm apart. Row spacing for the
largest maincrop varieties can be up to 50 cm.
Once sown, seeds can be covered in loose soil,
sand, compost, leaf mould or vermiculite. After sowing and covering, the
drills are ideally tamped or patted down to ensure good soil contact with the
seeds. Heat, drought and crusting of the soil surface can interfere with
germination and emergence. Birds can take seed and re-sowing may be necessary
when this occurs. Covering can prevent seed loss to birds.
Germination usually takes between 10 to 24 days,
depending on temperature and other factors, although under ideal conditions
it can occur in less than 10 days. Beetroot germinates relatively well at
high temperatures, but germination becomes slow and erratic at temperatures
below 7°C.
Beetroot seed has a relatively low germination
rate compared to other crop seed. The statutory minimum level of germination
for beetroot in the UK is lower than for most crops at 70%; although 50%
germination is accepted for Cheltenham Green Top, a long-rooted cultivar
grown since the seventeenth century. Seed packets usually contain a much
higher proportion of live seed, although the statutory testing is done when
the seeds are packed for sale and seed viability declines with time. Older
seeds will have lower germination rates and beetroot seed should be stored
for no longer than five years.
Three seed factors that negatively influence
germination have been identified: i) a mucilaginous layer that can surround
the seedball, ii) the ovary cap, and iii) the presence of chemical inhibitors
in the seedball.
A mucilaginous layer has been observed on beet
seedballs. This is particularly the case for sugar beet, where around 75% of
seed can have a significant mucus layer. The germination potential is lowered
for cultivars prone to having this layer. In experiments, seedballs with a
mucilaginous layer had a lower rate of germination, and a lower level of
final germination, compared to seedballs lacking one.
The ovary cap or operculum is a dome-shaped
structure that covers the embryo. It acts as a barrier to gas exchange. The
length of time that the operculum holds fast to the rest of the embryo varies
between cultivars. The amount of oxygen available to germinating seeds may be
limited in cultivars having tenacious operculum, which can slow development.
In experiments where the operculum has been softened through soaking, or has
been lifted and removed, germination rate has been increased. The effect is
most pronounced for cultivars having a mucilaginous layer.
The cork-like layer around the seeds in the
seedball contains substances that inhibit germination. These germination
inhibitors have been identified as phenolic compounds. They may contribute to
the good storage properties of beet seed, and prevent inappropriate
germination. However, they can take up to several weeks to de-activate after
sowing and result in asynchronous emergence. In an experimental study,
seedballs having a mucilaginous layer were found to have higher levels of
phenolic germination inhibitors.
The three physical and chemical factors outlined
above make germination erratic. In commercial operations, a lack of
uniformity in germination leads to a lack of uniformity in emergence and
subsequent product size. Seed factors affecting germination are therefore
considered when planning pre-sowing treatments.
Water and temperature are the main environmental
factors limiting germination. High water levels in the soil are inhibitory to
the rate of germination and emergence. In experiments, however, excess water
levels only affected seed viability when associated with high temperatures
(above 35°C). Below this temperature, the rate of seed emergence is only
slowed down. Excess water restricts gas exchange, reducing the oxygen
available to the seeds. Soils that hold water, such as heavy clays, may
therefore limit the rate of seed germination more easily than well-drained
soils.
Methods to boost germination early in the season
include warming the soil with cloches, fluid sowing, pre-soaking the seeds,
and sowing in modules (transplanting). Cloches or cold frames can be used in
gardens to enable the soil temperature for successful germination to be
attained earlier in the season. They can be left in place while seedlings
emerge.
Fluid sowing involves germinating seeds indoors
under ideal conditions, for example, in a box on absorbent paper, and then
mixing them into a jelly-like medium for sowing. At normal room temperature,
around 70% of the seeds of a typical beetroot variety will germinate in six
days, after which time they are ready for fluid sowing. This technique is
time-consuming, but it enables germination rates to be quantified. The jelly
medium protects the germinated seeds from being damaged and it can be made,
for instance, out of wallpaper paste mixed at half strength. Germinated seeds
are stirred into the jelly medium, which can be squeezed through a nozzle
into prepared rows and covered in the normal way.
Soaking beetroot seed in water prior to sowing is
recommended as a means of improving germination. An hour in water is said to
be beneficial, but it is usually recommended that seeds are soaked for up to
twelve hours or overnight in lukewarm water or water at room temperature
(around 21°C). Soaking acts to wash out the germination inhibitors present in
the cork-like layer of the seedball. Some growers suggest using running water
to remove the inhibitory compounds from the vicinity of the seeds, but this probably
only offers a marginal additional benefit and wastes water. After soaking,
the seedballs should be dried before sowing. Most modern lines of beetroot
tend to have good germination rates if sown in their year of purchase. In my
limited trials with fresh seed of several cultivars, I found that soaking
over a period of hours did not significantly improve germination rate.
However, this method is likely to be more beneficial when using seed that has
been stored for a year or more, with seed of unimproved, traditional or
heritage varieties, or when only a small amount of seed is available.
The corky layer can be rubbed off beet seed to
produce smooth round seedballs. This can help remove the mucilaginous layer
and germination inhibitors. In commercial operations, for example, decorking
or seed scarification can increase sugar beet seedling vigour. However, for
beetroot, rubbing the seedballs can damage the seeds and reduce germination
rate. Packets of modern F1 hybrid beetroot seed, in fact, often advise against
damaging the seedballs in any way.
Successive sowings of beetroot can be made every
three weeks during the growing season, to ensure a continuous supply of small
beets. Early-season quick-maturing cultivars are planting in spring (e.g.
April onwards in Britain). Cultivars that are resistant to bolting are
recommended for early sowing. Late maturing larger-rooted maincrop cultivars
are sown from mid-summer onwards, and the roots can be stored and used during
the winter. It is recommended that the last sowing should be timed at least
ten weeks before heavy frosts are expected.
Some thinning is nearly always required for
beetroot, because it germinates from multigerm seedballs. If every seed in a
seedball germinated, one to three seedlings would emerge per seedball. For
the most commonly grown beetroot cultivars, two embryos typically develop to
produce two seedlings per seedball. Two or more seedlings can therefore
emerge in the same station and adversely compete with each other.
Once seedlings are around 5 cm high, they are
typically thinned to 5 to 10 cm apart. Single plants of maincrop and
long-rooted varieties, however, are thinned to between 20 and 25 cm apart to
reach maturity. Dull and damp weather is traditionally recommended for
thinning operations. Thinned beetroot can be eaten steamed or in salads.
Beetroot mature more quickly when the plant stand is thinner.
Monogerm cultivars of beetroot have been bred in
recent years, which reduce the time-consuming labour of thinning. They have
only one viable seed per seedball and therefore do not need thinning, if only
one seed (seedball) is planted per station. Monogerm beetroot cultivars
include Monogram, Monopoly and Moneta.
All sugar beet seed is now monogerm. In the past,
machines were used to thin sugar beet rows after emergence. Today, seeds are
sown mechanically using precision drills and there is no need for subsequent
thinning.
Cultivated beets can be transplanted within
modules, so the roots are minimally disturbed. This is sometimes
advantageous. The first sowing of the year can be done in seed modules in a
greenhouse from February onwards, for instance, to avoid early cold
temperatures in the field. Transplanting is usually only recommended for
globe beetroot varieties. Modules are planted out, about 10 cm apart, when
seedlings are around 5 cm high. Up to three seeds can be sown per module,
with thinning leaving the most vigorous seedling. Transplanted seedlings can
also be used to fill gaps in rows due to poor germination or seed predation
by birds, or to fill odd spaces around an allotment. However, transplanting
can on occasion give poor results or malformed roots, and therefore direct
sowing is usually recommended as a first course of action where climatic conditions
are favourable.
Baron von Koppy first transplanted sugar beet, on
an experimental basis, in the nineteenth century. This method has been
adopted for cultivated beets and is still used today, especially in Japan and
China. Chinese gardeners reportedly transplant much of their beetroot early
in the season.
Beetroot can be grown in modules or boxes in
order to harvest the young leaves for salads. These can be grown in compact
units, as these plants are not being grown for their roots. Beetroot can also
be cultivated to harvest in containers. This works best for smaller
globe-shaped beetroot cultivars in containers that are ideally trough-shaped
and filled with at least a 20 cm of soil.
Beetroot grows best in a relatively cool and even
climate. Temperatures between 15 and 19°C (60-65°F) are ideal for
cultivation. Beetroot develops its deepest colours, highest sugar content,
and best root quality and shape in this relatively cool temperature range.
Beetroot's optimal temperature range is effectively the same as fodder and
sugar beet. These cultivated beets prefer cooler temperatures than the wild
sea beet from which they are descended. Leaf beets, however, can thrive in
warmer temperatures than beetroot.
Beetroot growth in early spring is constrained by
sub-optimal low temperatures. The use of cloches or horticultural fleece to
warm the soil and air around young seedlings can increase early growth rates.
The use of horticultural fleece, in one study, increased beetroot yields by up
to 50% in early spring. The fleece can be removed four to six weeks after
sowing.
Temperatures below 10°C (50°F) cause a
physiological shift from vegetative growth to reproductive growth, with the
storage root shrinking and nutrients being diverted to reproductive
structures. If low temperatures persist for over two weeks, particularly with
seedlings early in the season, bolting (premature flowering) can occur in the
first year's growth. Bolting resistance has been bred into beet cultivars to
reduce this problem early in the season.
Beetroot can tolerate light to moderate frosts,
which can help enhance the sweetness of the roots. However, severe freezing
conditions in late autumn and winter can damage the taproot. The roots must
therefore be harvested before heavy frosts appear in northern latitudes.
Beetroot cultivars with large roots grow best in the colder regions of
Central and Eastern Europe, partly because they are more frost tolerant.
Temperatures above 25°C (77°F) can adversely
affect the growth, colour, and development of beetroot. At higher than
optimal temperatures, the storage of nutrients in the roots is reduced,
leading to smaller root size, and impaired texture and flavour. Roots can
become stringy and tough in response to excessive heat. Some cultivars are
more tolerant of tropical conditions than others, however, and these are
recommended in warmer regions. Crimson Globe and Detroit Dark Red, for
instance, are cultivars that do well in warmer climates.
Cultivated beets can survive drought and salinity
better than most crops. This reflects the species' coastal origins. However,
supplying additional water can raise crop yield. The main aim of irrigation
in cultivated beets is to maximize productivity, by enabling an even growth
pattern to occur throughout the season. Maintaining moisture levels early in
the season is important, but overwatering is detrimental to growth.
Beetroot generally requires less water than leaf
beets. Frequent watering of beetroot leads to increased leaf growth, but this
is not necessarily accompanied by a proportional increase in root growth.
Overwatering can lead to excessive leaf growth and small roots. Waterlogged
soils can harm root development, encourage disease, cause minerals to leach
away from the roots, and create harvesting difficulties. The leaves of
waterlogged beetroot can turn red and photosynthesis can be affected,
resulting in plants that stop growing for a period of time. Moderate watering
is therefore advised, sufficient to prevent the soil from completely drying
out. In wet conditions, growing beetroot in raised beds enhances drainage.
Mulching can conserve soil moisture during dry weather.
Dry conditions over a period of weeks may
constrain plant growth and reduce yields. In dry soils, there is an increase
in the amount of zoning in the roots. Paler rings develop due to the lack of
moisture, while the roots start to become woody. Sudden irrigation or rain
after a period of drought can cause roots to split. Watering at a rate of
eleven litres per square metre every two weeks is recommended in the Royal
Horticultural Society (RHS) Encyclopaedia of Gardening.
Water is taken up by the fibrous roots that grow
from the main storage or taproot. Deep-rooted (long root-shaped) beetroot
cultivars and sugar beet can access water deeper in the soil and survive
drought better than shallow rooted (e.g. globe-shaped) cultivars. Irrigated
sugar beet produces higher sugar yields. Similarly, the natural sweetness in
beetroot is enhanced in plants that have been adequately watered.
Cultivated beets are tolerant of a wide range of
soil conditions, but they grow best in open sunny sites on well-drained
light, moist, friable and fertile soils. For beetroot, deep sandy loams are
ideal, especially those with a high organic content, which supplies natural
fertilizer and retains its moisture. Rich moist fertile soils produce the
best roots, although heavy clay soils may hinder root development. Although
beets can be grown under most conditions, for optimum or profitable yields
the application of fertilizer or lime is sometimes required. In particular,
sufficient levels of nitrogen, sodium, potassium and phosphorus are needed to
ensure good growth. As with all such operations, the cost of external
applications should be considered in terms of the added value to the crop.
The application of fresh manure, however, is not
recommended when preparing the ground for beetroot, because it can induce the
formation of multi-fang or thong-like roots instead of a single thick and
symmetrical taproot. Heavily manured or too-rich soils can also induce
cultivated beets to bolt.
Soil pH The
relative acidity or alkalinity of a soil is measured using the pH scale. A
neutral soil has pH 7.0, acid soils have a pH below 7.0 and alkaline soils
have a pH above 7.0. Beetroot prefers neutral to slightly alkaline soils.
Beetroot thrives when pH is between 6.0 and 8.0. However, lime should be
applied to acid soils below around pH 5.8, as root growth can be constrained.
Beets are less tolerant of soil acidity than crops such as beans or maize.
However, beetroot is more tolerant of alkaline soils.
Nitrogen
Nitrogen (N) is the most important fertilizer element applied to beets in
commercial production, because it is the element most likely to be deficient
in arable soils. Nitrogen is particularly important for healthy top growth,
improving the vigour and colour of foliage. In sugar beet production, this is
additionally important because many mechanical harvesters need to handle the
tops to lift the roots.
There is no single characteristic symptom that identifies
nitrogen deficiency. However, the foliage typically becomes light green in
appearance, then yellow, due to the disappearance of chlorophyll from the
leaves. This reduces photosynthesis and subsequently crop yield.
In sugar beet, nitrogen deficiency is often
observed in patches of stunted plants with small yellowing leaves. Nitrogen
deficiency in beets is most likely to occur on sandy or gravely soils. The
application of nitrogen fertilizer can greatly increase yields, particularly
on continually cropped soils. However, in sugar beet, excessively high levels
of nitrogen can reduce the quality of roots in terms of their sugar content.
This is the biggest dilemma of sugar beet nutrition: crops benefit from
additional nitrogen, but too much can depress the sugar yield and increase
the proportion of impurities in the extracted sugar.
In garden situations, enough nitrogen is usually
supplied by an organic-rich soil. Otherwise, nitrogen fertilizer can be
applied in moderation before sowing beetroot seed. Nitrogen can be put on as
sodium nitrate (nitrate of soda) in slightly acidic soils, or where available
sodium is limited.
Sodium Sea
beet typically grows in stony and sandy soils along coastlines. Such soil
conditions are still favourable by cultivated beets, although the beets that
have been selected for their taproots do best in soils with fewer stones. In
keeping with its seashore origin, beetroot tolerates moderate concentrations
of salt. Uniquely among crops, beets take up and use large quantities of
sodium (Na), which is required for optimal growth. Beta vulgaris,
particularly in its wild form, is regarded as a halophyte.
Common salt (sodium chloride) is applied on
beetroot in some areas as a fertilizer. Salt stimulates beetroot growth and
kills small weeds, which are generally less tolerant of salt than beetroot.
However, the application of salt on beetroot growing in heavy clay soils is
not recommended. Beetroot and sugar beet are among the few commercial crops
that can be grown in saline conditions, although it is difficult to obtain
uniform plant stands.
There are no obvious sodium deficiency symptoms,
but plants deficient in sodium are far more likely to show symptoms of
potassium deficiency.
Potassium High
levels of potassium (K) are required for optimum growth of beet roots. The
symptoms of potassium deficiency are often referred to as ‘scorch’. Patches
of dead tissue occur in leaves (chlorosis), which take on a dull olive green
to bronze appearance. Low sodium exacerbates the problem, while potassium
deficiency can be alleviated by the addition of both potassium and sodium to
the soil.
Potassium fertilizers can be applied in bands
beneath rows prior to sowing seed or alongside seed soon after sowing.
Slow-release fertilizers may be applied in the weeks before sowing. Potash
fertilizers are often recommended prior to sowing and Arthur Hellyer, in his
gardening guide, suggests an application of one part sulphate of ammonia, one
part sulphate of potash, and five parts superphosphate of lime, mixed and
applied at 100-130 g per square metre. Wood ash is also beneficial, forked
into the ground prior to sowing.
Phosphorus
Phosphorus (P) is necessary for vigorous early seedling growth in cultivated
beets. It is often in short supply in newly cultivated soils, but builds up
in soils after repeated fertilizer applications. Phosphorus deficiency is
therefore rare and only occurs when soils are extremely depleted of this
element. It is particularly uncommon in mature plants, but manifests itself
in seedlings through stunting and dark-green or purple-red leaf colour. In
older plants, the roots can also become stunted, while the taproot may form a
mass of fibrous secondary roots.
Commercial fertilizers often deliver several key
elements simultaneously, for example, N, P, K fertilizers. In garden
situations, however, in most cases adequate beet crops will be produced
without recourse to fertilizers.
Sulphur
Sulphur (S) is absorbed by plants in the form of sulphates. The symptoms of
sulphur deficiency are yellowing young leaves with irregular brown blotches.
However, enough sulphur usually falls on crops in rain, especially in
polluted regions. Sulphur deficiency is therefore rarely a problem in
cultivated beets.
Calcium
Calcium (Ca) is an important element for cultivated beets, although it tends
to be overlooked as it is usually found at sufficient levels in the soil. It
accounts for why cultivated beets preference for slightly alkaline soils and
their intolerance of acid soils.
The most characteristic symptom of calcium
deficiency in cultivated beets is tip-burn, with young leaves becoming
crinkled and reduced in size, and the growing point developing abnormally so
that lateral shoots appear. This deficiency is not caused by inadequate
calcium in the soil, but by the plant's inability to take it up. This can
occur in acid or saline soils, or soils that have been waterlogged with salt
water. Calcium can be added to the soil in the form of lime to redress the
nutrient balance.
Magnesium If
levels of N, P and K are adequate in sugar beet, another nutrient that might
be limiting yield will sometimes be magnesium (Mg). Intensive cropping
removes this element from soils. The symptoms of magnesium deficiency are
pale yellow and brittle necrotic areas in leaves (the latter distinct from
the softer dead tissue areas seen in potassium deficiency). Magnesium
deficiency is most likely to occur in hot summers for crops growing on sandy
soils.
Boron The
most frequent nutrient deficiency encountered in cultivated beets is boron
(B) deficiency. A deficiency of this micronutrient is also referred to as
black spot, heart rot, dry rot or canker. Boron deficiency results in stunted
plants, the deformation and death of the growing point, and slow growth. The
crown of the root becomes hollowed and blackened, due to water accumulation.
Rough black spots can appear on the roots. In beetroot, this gives the roots
a bitter taste. The roots may eventually become entirely discoloured,
hollowed or split. The yield and quality of cultivated beet roots can
therefore be severely affected. Boron deficiency can also result in corky
growths on the shoots and stalks. Roots from boron deficient plants store
poorly.
Boron deficiency arises due to either a lack of
boron in the soil or an inability to take it up from the soil due to
unsuitable growing conditions. A lack of moisture aggravates boron
deficiency, and it most commonly occurs on chalky or heavily limed soils that
have dried out. Maintaining moisture levels in the soil and avoiding excessive
liming helps plants to obtain boron from the soil. Small amounts of borax
(sodium borate) can be added to the soil to alleviate problems caused by
boron deficiency. Alternatively, sprays of borax solution can be applied to
the foliage. However, the application of too much boron may be toxic to
subsequent crops. Plants that naturally accumulate boron, such as sweet
clover, can also be used to enrich the soil, particularly when they are grown
as a green manure. Seaweed is used as a valuable source of green manure on
cultivated Beta vulgaris in coastal areas.
Manganese and other trace elements A
deficiency of manganese (Mn) in the soil causes yellow or necrotic blotches
to occur between beetroot leaf veins. This mainly affects older leaves and is
most prevalent in very alkaline soils. It can be cured by the addition of
fertilizers containing manganese.
A number of other micronutrients or trace
elements are required for the optimum growth of cultivated beets. The main
ones being chlorine (Cl), copper (Cu), iron (Fe), molybdenum (Mo) and zinc
(Zn). These are rarely deficient in soils using for beet cultivation. The
presence of nutrients and micronutrients in cultivated beets helps to make
them such health-promoting vegetables (see Chapter Seven).
CAB International’s Crop Protection Compendium
lists 67 major pests of cultivated Beta vulgaris. These include weeds,
insects, nematodes, and fungal and viral pathogens. Cooke (1993) lists 56
types of sugar beet pest, excluding weeds. However, pests of cultivated Beta
vulgaris are largely sporadic in their impact. Beetroot under normal
circumstances has relatively few pest or disease problems.
Weeds Weeds
compete with beetroot for space, light, water and nutritional resources in
the soil, particularly during the early part of the season. They can reduce
yield if left unchecked. Regular hoeing in gardens and allotments prevents
weeds competing with beetroot. When hoeing, care should be taken not to
damage the roots. Applications of weedkillers (herbicides) provide control in
larger-scale and commercial plantings. The weeds in the CAB International
listing include amaranth or pigweed (Amaranthus retroflexus),
chickweed (Stellaria media), cleavers (Galium aparine),
dandelion (Taraxacum spp.), Johnson grass (Sorghum halepense),
knotweed (Polygonum aviculare), nettles (Urtica spp.),
meadowgrass (Poa annua) and ryegrass (Lolium spp.). In sugar
beet, 70% of weeds are typically broad-leaved plants and 30% are grasses.
It is plants in the Chenopodiaceae or goosefoot
family, however, that are the major weed pests of cultivated Beta vulgaris.
This is not surprising considering that Beta vulgaris is itself is in
Chenopodiaceae. Plants in this family tend to thrive under similar
conditions. Fat hen (Chenopodium album) is probably the biggest weed
problem in sugar beet and beetroot. Weedy forms of Beta vulgaris or
'weed beets' have in recent years become a particular problem in sugar beet
fields, especially in France and the more southern areas of Europe. Weed
beets can be bolters (prematurely setting seed in their first year’s growth
without producing useful roots), plants self-seeded from previous cultivation
or hybrids. Hybrid weed beets result from pollination between beet plants
growing wild around agricultural land and sugar beet crop plants. They tend
to adopt an annual growth pattern, competing with the crop for resources and
bolting to spread seed that furthers the problem.
Weeds are a particular problem early in the
growing season, when they compete for resources (e.g. moisture, light, soil
nutrients) with beet seedlings. Herbicides are sprayed predominantly at this
time to control weeds. However, weeds in the Chenopodiaceae and, in
particular, weed beets respond to particular herbicides in the same way as
cultivated beets. They are difficult to control because the herbicides that
control them best can also damage crop plants. The control of such weeds has
been a desirable goal in commercial beet production. This is why the first
transgenic or genetically modified Beta vulgaris was sugar beet
modified to be resistant to particular herbicide groups (e.g. glyphosates).
Transgenic herbicide-resistant sugar beet can be sprayed with these
herbicides, thereby controlling weeds without damaging the crop. This has
provided great benefits to sugar beet growers. However, concerns have been
expressed about the environmental impact of the changed herbicide spraying
regime and the evolution of resistance in weeds to the herbicides that are
being repeatedly sprayed on transgenic crops.
Nematodes The
beet cyst nematode (Heterodera schachtii) was one of the first pests
observed to limit sugar beet yields. It was described in the 1880s, in beets
grown in short rotations in Germany. Beet cyst nematode is now a major pest
of sugar beet worldwide, and is also a pest of fodder beet and beetroot. It
invades the roots, stunting their growth. Resistance to beet cyst nematode
has been bred into modern lines of sugar beet through the transfer of genes
from the wild species Beta patellaris (in the section Procumbentes
of the genus Beta).
Root knot nematode (Meloidogyne incognita)
and species of stubby root nematode (Trichodorus spp.) adversely
affect the roots of cultivated beets, particularly early in the growing
season. Stubby root nematodes cause the roots to fork or fang. In commercial
and garden situations, lengthening the rotation is the best method to reduce
damage due to nematodes.
Insects No
single insect pest consistently attacks cultivated beets. However, a range of
species can potentially damage them. This occasional damage can be severe.
Many of the insects attacking beets occur in the
family Lepidoptera (moths and butterflies). Larvae of beet webworms (e.g.
Hymenia perspectalis, Loxostege sticticalis and Spoladea recurvalis) feed on
leaves and roots. They construct a protective shelter by rolling a leaf and
tying it together with webs. Cutworms (e.g. Agrotis spp. and Peridroma
saucia) are noctuid moth larvae that feed on the lower leaves and crowns
of beet roots. After attack by cutworms, the stem bases and lower leaves are
visibly gnawed. Beet armyworm (Spodoptera exigua) larvae can defoliate
crops in the USA, especially when migrating from pigweed. Lepidoptera larvae
can be picked off cultivated beets and destroyed in gardens and small-scale
commercial operations.
Flea beetles (e.g. Chaetocnema confinis)
are small jumping beetles, which eat holes in young leaves and can seriously
damage seedlings. The white larvae of beet leafminers (e.g. Pegomya
hyoscyami) feed on internal leaf tissue, causing yellowish blisters on
the foliage. Heavily damaged leaves can be picked off and destroyed to
prevent infestation spreading, although leafminers do no damage to the roots.
Aphids (e.g. Aphis fabae and Myzus
persicae) form dense colonies on the shoots and leaves of Beta
vulgaris. They can cause direct damage by feeding and extracting plant
sap, but are primarily a pest of beets because they act as vectors for virus
yellows diseases. They transmit virus from crop to crop and spread it within
a crop. Aphid species are particularly significant as pests of beetroot being
grown for seed. Controlling aphids with insecticides is the main method of
preventing virus infestations in sugar beet. However, heavy insecticide use
has resulted in aphids evolving insecticide resistance, which has led to a
resurgence of virus disease problems in sugar beet.
The beet leafhopper (Neoaliturus tenellus
[Circulifer tenellus]) is a pest of beetroot because it transmits beet
curly top virus (curly top disease). The beet leafhopper and the virus it
transmits are primarily found in the USA.
Viral diseases Virus
yellows is a group of aphid-transmitted viral diseases that affect all
cultivated beets. Virus yellows was first described in the 1930s affecting
sugar beet. It causes foliage to become yellowed or necrotic. Leaf veins may
be particularly affected. This reduces photosynthetic efficiency, root system
development, and sugar yield and quality. It was subsequently found that
virus yellows comprises a complex of closely related viruses: beet yellows
virus (BYV), beet mild yellowing virus (BMYV) and beet western yellows virus
(BWYV). These viruses have different distributions and slightly different
symptoms. They are rarely a problem in beetroot.
Beet mosaic virus (BtMV) is another
aphid-transmitted beet virus. It causes flecking and mosaic patterns on beet
leaves, and eventually major leaf abnormalities.
Curly top disease is caused by beet curly top
virus (BCTV), which is transmitted from plant to plant by feeding beet
leafhoppers. The symptoms of curly top disease include warty leaf veins and
rolled, brittle and twisted foliage. Plants become stunted and the root
system is reduced in size. Curly top disease caused major losses in sugar
beet in the USA, until the introduction of resistant varieties in the 1930s.
Today, all sugar beet cultivars incorporate resistance to curly top disease.
Not all beet viruses, however, are transmitted by
insect vectors. Some minor viruses of sugar beet are transmitted by
nematodes, and one significant pest problem arises through an association
between a virus and a fungus. Beet rhizomania is caused by the beet necrotic
yellow vein virus (BNYW), which is transmitted by the fungus Polymyxa
betae. Rhizomania is largely restricted to species of Beta because
of the narrow host range of the fungus. The disease was first described in
Italy in 1952, and it is now widespread. Rhizomania can cause severe yield
losses in sugar beet. The virus was named after the leaf symptoms, but the
major economic damage is done to the roots. Rhizomania (meaning ‘leaf madness’)
is characterized by the abnormal proliferation of lateral roots, producing a
mass of fibrous roots known as bearded root.
Fungicides have provided the main means of
control for rhizomania in sugar beet. However, resistance has been found in
wild Beta species that is being incorporated into breeding programmes,
and genetic engineering techniques are being used to produce 'immune' plants
through the incorporation of viral coat proteins in the plant genome.
Fungal pathogens
There are a number of fungal diseases that affect
cultivated beets, including mildews and the organisms that cause damping off,
scab and leaf spot.
Downy mildew (Peronospora farinosa) causes
red-rimmed spots on the leaves of beetroot. It thrives during periods when
the roots dry out or when plants are growing slowly, and spreads quickly in
the field during cool and humid weather conditions. Downy mildew affects the
tops of beetroot, causing discolouration. It can spread to the crown and top
of the taproot. It can also infect the flowers and seedball, and it is a
seed-transmitted pathogen. Powdery mildew (Erysiphe betae) has
symptoms similar to downy mildew. The fungi that cause both downy and powdery
mildews in cultivated beets are restricted to Beta species. Resistance
to powdery mildew has been bred into sugar beet using genes from sea beet (Beta
vulgaris subsp. maritima).
A range of different soil-born fungal pathogens
cause damping off or blackleg in cultivated beets (e.g. Pleospora betae,
Pythium ultimum and Phytophthora spp.). Seedlings and young
plants rot at soil level, collapse and die. Damping off is most prevalent in
wet weather, in early spring plantings, and in poorly drained soils. It is
rarely a problem in sugar beet today, because of the use of fungicides and
resistant varieties. Individual rots are often distinguished within this
general condition, including rhizoctonia disease (Rhizoctonia solani),
wet rot (Phytophthora megasperma), phoma (Phoma betae), violet
root rot (Helicobasidium purpureum), sclerotium root rot (Sclerotium
rolfsii) and others.
Scab (Streptocyces scabies) affects many
vegetables, including cultivated beets. Beetroot is particularly susceptible
to scab, which causes rough corky spots and warty growths on the skin of the
root. It can be prevented by ensuring that soil pH is near neutral and by
rotating crops.
Cercospora leaf spot (Cercospora beticola)
is a widespread and destructive foliar disease of cultivated beets. It is one
of the most common diseases affecting beetroot and can cause significant economic
losses in sugar beet. Cercospora causes small brown spots with reddish-purple
borders to appear over leaves and stems. Heavy infection causes leaves to
become yellow and drop off. Applying potash before sowing can help prevent
leaf spot, as can crop rotation. Resistance to Cercospora leaf spot was first
bred into sugar beet in the 1920s by Italian scientists, through crosses with
resistant sea beet. More recently, beetroot cultivars have been bred with
resistance to Cercospora leaf spot. Leaf spot in beetroot can also be caused
by other fungi (e.g. Ramularia beticola). Leaf spot is more prevalent
in wet conditions when plants are closely spaced.
Slugs and snails
Molluscs can do considerable damage to the foliage of cultivated beets,
particularly those grown in gardens and allotments. Slugs (e.g. Deroceras
reticulatum) make holes in the leaves, especially when conditions are
damp on heavier and poorly drained soils. Slugs can be a particular problem
when roots are left in the ground late in the season. Snails can also, on
occasion, be a problem under wet conditions.
Birds and mammals Birds
eat beetroot seed and seedlings. Sparrows (Passer spp.) can be a
problem in gardens, while pheasants (Phasianus spp.), partridge (Perdix
perdix) and pigeons (Columba spp.) are among the main bird pests
in sugar beet fields. Netting can keep birds away from seed and seedlings in
gardens and allotments. Birds can eat their way down a row of seeds, but not
all the seeds are necessarily destroyed. Charles Darwin, in The Origin of
Species (1859), records beet seed germinating after passing through the
digestive system of birds. He fed seeds of various crop plants to birds of
prey in the Zoological Gardens in London and noted that two beet seeds grew
after having been retained by a bird for two days and fourteen hours,
respectively. This represents a minor route by which wild and weedy Beta
vulgaris can disperse.
A number of mammals are pests of sugar beet,
including moles, mice, rats, rabbits and deer. Much of the damage caused,
however, is non-lethal defoliation from which plants can recover.
Rotating crops is an important factor in reducing
the incidence of pests and diseases in cultivated beets. Yields of sugar beet
were significantly reduced by nematodes, for instance, before the practice of
rotation became established. Rotation, in combination with crop hygiene, is
particularly important in reducing the incidence of damping off, rot and
other fungal diseases.
Beetroot can easily be fitted into planting
schemes in a garden or allotment, for example, being sow on ground from which
heavily manured crops like potatoes or beans have recently been harvested. By
following on from a well-manured crop, beetroot can be grown in soil with
good water-retention properties. Green crops and potatoes are demanding of
nitrogen in the soil and benefit from well-rotted animal manure. Fresh manure
is harmful to root development in beetroot and crops such as carrots, turnips
and parsnips. Therefore, green crops and potatoes are typically followed by
root crops in crop rotation systems.
Rotation in a three or four year cycle with
legumes is usually recommended for cultivated beets. A three-year garden
rotation could involve, for instance, firstly, the rotation of blocks of
cabbages and other brassicas along with lettuces and other salads; secondly,
potatoes followed by broccoli and other winter greens; and thirdly, carrots,
beetroot and other root crops, along with peas and beans.
A number of companion plants to grow with
beetroot are suggested in The Complete Book of Vegetables, Herbs and Fruit.
Beetroot is said to flourish in the company of kohlrabi and brassicas,
carrots, cucumbers, lettuce, onions and most beans, but not tall runner beans
that could shade them. Dill or Florence fennel planted nearby may attract
predators that prey on insect pests of beetroot. Beetroot combines well with
many other crops and is quick growing, making it good for serial cropping and
intercropping within a rotation.
Beetroot are harvested from the early summer to
late autumn in their first year of growth. The roots can be harvested over a
period of time, to give beets ranging in size from small to large and mature.
It usually takes around 60 to 90 days for beetroot to reach full maturity.
Beetroot can be harvested when required and left in the ground until the
first heavy frosts of autumn. Mature roots can survive mild frosts, but can
suffer freezing damage during heavy frosts. The leaves start to fall away
from an upright position when beets reach maturity.
Beetroot must be lifted carefully, because
bruised and broken roots bleed and are of diminished culinary value. Beetroot
or garden beet is usually harvested with its leaves by hand, and either used
domestically or sold fresh in bunches tied around the stems or leaves. For
market sale, dead leaves are usually removed and the roots washed, for
example under a hosepipe, rather than being scrubbed. The leaves are
traditionally twisted off above the crown. If the leaves are not wanted in
the kitchen, their high mineral content (e.g. magnesium) makes them a useful
addition to the compost heap.
Small beets or minibeets (below 5 cm) may be
harvested about two months after sowing, while mature full-size beets may be
harvested after three months or longer. Final root size is due to variety and
spacing, and not degree of maturity. In southern Europe, beets can be left in
the ground overwinter. In mild climates, a layer of straw around 15 cm thick
can be placed over the soil where roots are left in the ground overwinter. In
northern latitudes, where most beetroot is now grown, the beets must be
lifted and stored before midwinter, because of potential damage from severe
frosts.
In commercial operations, beetroot and sugar beet
are mechanical harvesting in bulk. The first mechanical harvesters for
cultivated beets were introduced in the 1930s in the USA. By the 1950s, the
entire US sugar beet crop was harvested mechanically. Little sugar beet
worldwide is now harvested manually. Single or multiple-row harvesters are
available, which operate using two different methods. Beets can be lifted
mechanically using the tops. Good top development is encouraged in beets
harvested by this method. In the other method, a flail removes the tops prior
to harvest. The beets are then harvested from the soil like potatoes. This
method can be used on modern beet cultivars having small top development.
Eastern and Central Europe has historically been
associated with the large-scale cultivation of maincrop beetroot. The major
beetroot producers today are Russia, Poland, France, Italy and the USA.
Northern Europe and North America produce the bulk of the commercial crop.
Their combined commercial production (excluding Eastern Europe) is around
900,000 tons, according to CAB International figures. In most other areas,
beetroot is mainly grown in market gardens or for home consumption. In
Eastern Europe a large proportion of the beetroot crop is home-produced. In
Russia, for instance, family dachas (small country houses and gardens) are
used to grow beetroot and other vegetables. Recently, a travel company
offering coach trips between St. Petersburg and Moscow started operating
under the name Beetroot Bus Tours, because of the prevalence of beetroot
fields en route.
The major areas of beetroot production in the USA
are New York, Wisconsin, Oregon and Texas. Most US beetroot goes straight to
the food processing industry, but some reaches the fresh market. The
commercial crop is harvested mechanically, but the crop for the fresh market
is often hand harvested. Mechanical harvesters first cut off the bulk of the
leaves and then crop the plants within around 5 cm of the crown, with a
second harvester following to lift the roots into bulk trailers. Around
14,000 acres of beetroot were grown annually in the late 1990s in the USA.
Figures from the University of Georgia show that processed beet yields 18 to
25 tons per acre, while fresh market beet yields 140 to 200 cwt. per acre.
Commercial beetroot fall into three grades for the US market; grade 1 being
below 5 cm (up to 2 5/8 inches) in diameter, grade 2 being around 5-7 cm (2-2
5/8 inches) and grade 3 being around 7.5-10 cm (3-4 inches). Grade 2 beets
are consistently available season long, but grades 1 and 3 have greater seasonal
variation. For beetroot sold fresh, the USDA (United States Department of
Agriculture) set a maximum permissible weight loss of 41% from harvesting to
point of sale, although this is 7% if roots are sold with tops as the leaves
soon wilt due to moisture loss.
In garden situations, Hellyer estimates that
beetroot typically yield around 2.5 kg per square metre or 1.3 kg per metre
of row. CAB International data gives typical commercial yields of around 15.3
t/ha of beetroot in Mediterranean and tropical conditions.
The world's single heaviest beetroot, according
to the Guinness Book of Records, weighed 23.5 kg (51 lb 9.4 oz) and
was exhibited by Ian Neale at the National Giant Vegetable Championship,
Shepton Mallet, in Somerset, England, on 7th September 2001.
Beetroot, fodder beet and sugar beet store well
and are amenable to long-distance transport. Fully mature beets store better
than immature roots. Beets have traditionally been stored outdoors on farms,
in covered heaps or buried in hogs or clamps. Fodder beets have often been
stored in bulk in silos. However, when grown commercially, beets are now
moved indoors and stored under controlled environmental conditions.
Beetroot needs around 12 to 16 weeks of growth to
reach a sufficient maturity for storage. Long and cylindrical rooted
cultivars are usually considered better for storing when mature, while
cultivars with globe-shaped roots are considered better for immature use, but
all beetroot cultivars store reasonably well. Before storing, the leaves are
either twisted off or cut 5 to 8 cm above the crown. Beetroot can be stored
in strong boxes in sand, earth, or sawdust, in a cool, frost-proof location.
Under favourable conditions, beetroot can be stored up to five to six months.
The best storage conditions for beetroot,
described in Stanley Kay's Postharvest Physiology of Perishable Plant
Products, are in cool temperatures (0 to 5°C) and high humidity (90 to
95% relative humidity). High humidity is important because the maximum
acceptable loss of water is 7% from stored roots, or 5% when beetroot is
bunched with leaves, before beets are considered unmarketable. Beets (no
leaves) are comprised of around 88% water. High humidity minimizes water loss
during storage. The freezing point for topped beetroot, with leaves removed,
is -0.9?C, while for bunched beetroot is it -0.4°C. Below these temperatures,
freezing damage will occur. High levels of carbon dioxide may also be detrimental
to beetroot storage. In high levels of carbon dioxide (30-70%), beetroot
increases its respiration rate, which leads to a higher metabolic rate.
Storage methods utilizing high carbon dioxide are therefore inappropriate for
beetroot, while some degree of air circulation that prevents carbon dioxide
from building up may enable beetroot to be stored for longer.
Topped beets for the fresh market in the USA are
typically graded, washed and packaged in polyethylene bags. They are stored
for up to five months at below 5°C (around 32°F) and 90-95% relative humidity
before being sold. Beetroot should not be stored in large bulk, but ideally
in pallets or crates that allow good air circulation around each beet. These
are mostly marketed within six months, enabling the crop to be sold
throughout autumn and winter. If beetroot is to be kept for longer,
preservation is required.
Commercially grown beetroot is mainly preserved
before sale, by being either boiled or pickled. In the USA, boiled and canned
beets are common, while in Europe, mini-beets or sliced beetroot pickled in
glass jars is more prevalent. The Germans and British, in particular, consume
large quantities of beetroot pickled in malt vinegar. Industrial processing
involves cleaning, slicing or dicing; then steaming or boiling, which cooks
and sterilizes the beets; followed by mechanical skinning. The beetroot are
then vacuum-sealed in a preserving solution such as vinegar.
During World War II, beetroot was found to be one
of the most satisfactory dehydrated vegetables for military and civilian use.
It can still be bought in freeze-dried form in health food stores, because
beetroot is undergoing a revival as a health tonic (see Chapter Six).
When beetroot is grown as a vegetable, it is
treated as an annual and harvested after the first growing season. However,
to produce seed, it must be allowed to complete its two-year life cycle. When
raising beetroot for seed, the crop can be sown in spring or early summer and
grown normally during its first season.
Beetroot requires a cooling period (vernalisation)
at the end of the first season's growth before it will flower in the second
season. Beetroot seed is produced commercially in colder climates, in
northern Europe and North America, so that this period of cooling is easily
achieved and where pest and disease problems are minimized. In temperate
areas, two weeks at between 2 and 10°C should induce flowering.
For seed production, beets are lifted at the end
of the first season and the best material is selected. These roots are stored
in sand or earth in a cool but frost-free place. They are then planted out in
the following spring and allowed to grow until they produce seed.
The guidelines of the Heritage Seed Library, part
of the Henry Doubleday Research Association (HDRA), suggest replanting roots
of beetroot in blocks with plants 30 cm apart. The crowns are positioned at
soil level and watered well to encourage re-rooting. Beetroot is
self-incompatible and will not self-fertilize. Therefore, blocks or rows of
beetroot of the same cultivar are necessary to produce seed. Different
beetroot cultivars should also be isolated when grown for seed to avoid
hybridization and maintain varietal purity. Although pollination is mainly by
wind, Beta vulgaris flowers produce nectar and are visited by insects.
In gardens, where large isolation distances are often not possible when seed
saving for personal use, horticultural fleece can be used to isolate blocks
of flowering plants to help reduce cross-fertilization.
Sugar beet seed production is an industry in
itself. Plants that are used to produce seed are known in their first year as
stecklings. These are carefully chosen from the available plants. Stecklings
are harvested and stored without tops like other sugar beet, but are then
mechanically transplanted into different fields to begin a second year's
growth. Alternatively, the roots can be left in the ground to overwinter
after the first year's growth, with the plants being allowed to grow on into
their second season. This can only be done in northern latitudes where the
temperatures become cold enough for vernalisation, but is a method that
significantly reduces labour costs. As the second year's growth begins, the
main shoot tip is removed to encourage side branching, which increases the
number and quality of the seed produced.
All the cultivated forms of Beta vulgaris
(e.g. leaf beets, beetroot and sugar beet) can readily interbreed. Wind-born
pollen can fertilize beet flowers over long distances. Commercial seed crops
of beetroot, therefore, are often grown several miles away from sugar beet or
fodder beet seed crops because cross-pollination could ruin seed purity for
one or other crop. Minimal isolation distances of up to 3,200 metres have
been stipulated for sugar beet seed crops in order to maintain varietal
purity during seed production. In the UK, for example, the Beet Seeds
Regulations 1985 (as amended in 1989) state that the minimum distances from
neighbouring plants for the production of seed for sugar beet and fodder beet
should be 1000 metres away from other Beta vulgaris pollen sources.
The flower spike is harvested when all the
seedballs have fully developed. The seedballs are removed by pinching them
off the stalks and they are stored intact. The HDRA guidelines suggest that
beetroot seed can be stored for up to six years under cool dry conditions.
Seed production is difficult under tropical conditions, so seed is imported
into many countries where beetroot is now grown.
A recent theory suggests that the location on the
flower spike from where seeds are harvested may be significant. Research in
China has found that wheat seed collected from the centre of the spike grows
into plants that have significantly higher yields than wheat plants grown
from seed collected from the top or bottom of the spike. Stephen Coleman has
suggested that this might also apply to other crops having seeds spaced out
along spikes. Seed position on the spike of Beta vulgaris, for
instance, may have been a factor in the differentiation of this species into
different cultivated forms selected for either top or root growth. Localized
selected seed experiments with Beta vulgaris may become an interesting
area of exploration.
Crop biodiversity is preserved in situ,
especially in a crop’s centre of origin and genetic diversity, in seedbanks,
botanical collections and gardens. Seed saving organizations around the world
are playing an important role in preserving traditional, heritage or heirloom
crop varieties. The Heritage Seed Library of the HDRA in England, for
example, maintains seed for many crop varieties that are no longer registered
for sale in seed catalogues. The Heritage Seed Library maintains several
traditional beetroot varieties, which are available to amateur gardeners on paying
a subscription to the library. Because European Union (EU) legislation states
that seeds not listed on National Seed Registers cannot be sold, seeds for
many heritage varieties must be swapped or exchanged in this manner in order
to preserve crop biodiversity.
It is important that heritage varieties continue
to be cultivated. Agriculture is culture in all its aspects. History is
present in heritage varieties. A garden of traditional and heirloom varieties
is a fascinating living museum. It offers clues to how our ancestors lived
and how they improved food plants, and it propagates a unique aesthetic
beauty. Beetroot has in the past, for instance, been grown for its ornamental
value far more than it is today. Varieties that have dropped out of fashion as
food plants still look beautiful in gardens. The taste of traditional
varieties is also different to modern cultivars, which like all horticultural
crops are today mainly bred to satisfy the demands of intensive agriculture,
food processors and supermarkets.
Heritage varieties offer a unique genetic
resource for future generations. Genes from them, for instance, may encode
traits that may be beneficial against emerging pests and diseases or to help
crops adapt to climate change.
A rich genetic heritage of wild Beta vulgaris
and related Beta species still exists in Europe. However, many of the
natural habitats where these plants occur are under threat. It is important
to preserve this genetic material in its natural habitat, within in in
situ conservation projects, as well as in seed banks and botanical
collections. Within the genus Beta, species in the section Procumbentes
are largely restricted to the Canary Islands, where tourism is a threat to
genetic diversity through habitat destruction. The only species in the
section Nana (Beta nanae) is restricted in distribution to
snowy patches above 2000 metres on several Greek mountains. Nature reserves
will be needed for its long-term survival. Several Beta species in the
section Corollinae are potentially threatened in central Asia, for
example, by changing farming practices. Meanwhile, in the section Beta,
populations of the perennial species Beta patula are mainly found on a
small island near Madeira; while an unusual polyploid strain of Beta
macrocarpa is restricted to salt mine workings in the Canary Islands,
which are vulnerable to pressures from tourism.
Germplasm from wild Beta species has
already been used to make improvements to sugar beet in terms of pest and
disease resistance. It is therefore important to preserve all existing
germplasm within the genus Beta for future breeding programmes. An
International Data Base for Beta (IDBB), funded by the European Commission,
is in the process of being established (2004), which will facilitate access
to germplasm held in a decentralized network of genebanks around the world.
Molecular marker techniques will be used to look for novel and potentially
useful genetic diversity, while material will be evaluated for resistance to
root rots and fungal pathogens, viral diseases, and for tolerance to saline
and drought conditions.
Sugar beet breeders in Europe and North America
maintain collections of wild and cultivated Beta vulgaris from its
area of origin in the eastern Mediterranean, and from its secondary centres of
diversity. The International Board for Plant Genetic Resources (IBPGR) has
given Beta vulgaris high priority as a species needing preservation,
due to a rapid erosion of its diversity in the wild.
Most beetroot breeding work is done in temperate
countries, but some is also done in southern China and northern India. The
traits breeders aim to incorporate include improvement in the speed of root
formation, the limitation of leaf production, the production of homogeneous
colour, good symmetrical shape and appearance, improved taste
characteristics, and the prevention of bolting.
Beta vulgaris was
among the first crops to be modified by genetic engineering. Sugar beet has
been modified to be resistant to herbicides, as previously noted. With world
sugar production exceeding demand, there has been little incentive to modify
sugar beet to increase yield. Herbicide-resistance makes weed control in
sugar beet more efficient and reduces on-farm costs.
There have been sound commercial reasons for concentrating
on herbicide-resistance as a trait in transgenic crops. It helps, for
instance, to preserve the market share for brand-name herbicides. Monsanto,
for instance, have modified a range of crops to be resistant to glyphosate
herbicide at a time when its Roundup glyphosate herbicide is coming out of
patent. Roundup has been one of Monsanto's most profitable products over
recent years. Farmers must sign a licensing agreement with Monsanto when
growing the company's Roundup-Ready crops, in which they agree to spray only
Roundup herbicide, and not generic glyphosate products, on these crops. New
factories producing Roundup are springing up around the world, most notably
in South America, to meet demand for increased Roundup spraying on Round-up
soybeans, maize, cotton, oilseed rape and sugar beet.
Although herbicide-resistant sugar beet is being
grown successfully in the USA and other countries, its introduction into
Europe has been delayed due to concerns that its cultivation will be
detrimental to the environment. Countryside and agriculture are much more
intrinsically linked in Europe than in North America. In an extensive
three-year programme of farm-scale evaluations of transgenic crops in the UK,
it was found that herbicide-resistant sugar beet was sprayed with more
herbicide than conventional sugar beet, reducing weed biomass sixfold late in
the season, with detrimental effects on biodiversity. Reductions in seed and
insect food could have serious long-term effects on bee, butterfly and bird
populations. In parts of Europe there is a move to see farmers not just as
producers of food but also as custodians of the countryside; a view that
acknowledges the economic importance of rural tourism. When growing a crop
that is already overproduced, moves towards methods of cultivation that
enable crop production and nature to co-exist need to be encouraged. The
scorched earth, weed-free transgenic crop route is out of step with this way
of thinking.
Other concerns expressed about the cultivation of
transgenic sugar beet include gene flow and the increased possibility that
resistance will develop in weeds to herbicides. Transgenes could easily
spread from transgenic sugar beet to other cultivated and wild Beta
vulgaris plants, all of which readily interbreed. The exchange of genes
between bolting sugar beet and weeds has been demonstrated in France, where
hybrid weed beets are a significant weed problem. The acquisition of
herbicide-resistance genes could make weed beet an even greater problem. The
spread of herbicide-resistant transgenes from one sugar beet crop to another
was first reported in Europe in 2000.
The first wave of transgenic crops was primarily
modified for herbicide-resistance. However, a wider range of modifications
are now being made to crops. Sugar beet, for instance, is now being modified
for resistance to the viral pathogen Beet Necrotic Yellow Vein Virus (BNYVV)
and resistance to nematode pests.
Transgenic sugar beet could soon be developed
with a modified sugar content. Work in Europe, for instance, is underway to
produce a range of sugar molecules called fructans in sugar beet roots. Novel
fructans will be designed to meet a range of needs as functional foods or
food ingredients, including low-calories sweeteners, dietary fibre or bulking
agent in processed food. Fructans can also be used as raw materials in a wide
range of non-food products such as biodegradable plastics, detergents and
adhesives, and in cosmetics. Such modifications would effectively convert
sugar beet into a new crop. Sugar beet farmers in Europe would benefit from
diversification and increased markets, at a time of sugar overproduction and
when their subsidies for growing sugar are being threatened by a World Trade
Organization (WTO) ruling (May 2004). Beet may become an important crop in
which to produce novel chemicals for industrial applications.
Sugar beet has been put to a range of uses over
the years. In addition to refined sucrose and sweet products, the tops and
pulp have been used as animal fodder, the dried pulp has provided a coffee
substitute, and its by-products have been used to manufacture industrial and
pharmaceutical products. Its juice can be processed into a tough varnish with
industrial applications, for example, while sugar beet is a source of citric
acid. The cosmetics industry makes extensive use of citric acid, which is
added to products to help them match the pH of the skin.
Beet crops may become increasingly used in the
production of biofuels. The technology for this is already in place. The
gasohol that drives cars in Brazil, for example, is made using sugar cane.
Using the same principle, sugar beet is one of the crops that can produce
bioethanol in Europe. Mixtures of bioethanol and petrol are used to fuel cars
in some European countries.
Biotechnology is extending the industrial uses of
sugar beet by-products. Beet pulp is a raw material used as a substrate for
the culturing of bacteria. The ferulic acid naturally found in beet pulp, for
example, can be converted into vanillin by a species of soil bacterium in the
laboratory. Vanillin is the most important component of vanilla essence. A
range of industrial products, including ethylene fuel and polyurethane foams
could be produced from sugar beet with the aid of biotechnology.
The techniques of tissue culture and genetic
engineering developed for sugar beet are applicable to beetroot. Tissue
culture involves the production of clonal regenerants from tissue taken from
a plant; usually undifferentiated callus tissue from the cotyledon of a plant
embryo. Regenerants grow into normal plants. They are easily screened in
breeding programmes and are ideal for genetic manipulation. An additional
advantage of large-scale tissue culture is that it gives rise to somaclonal
variation or novel genetic material for plant breeders to exploit. Beetroot
was included to a limited extent in early studies of regenerating Beta
vulgaris in tissue culture, although most work has been done on sugar
beet. Sabir and Ford-Lloyd included a fodder beet and four beetroot cultivars
in their study of the mass production of regenerants in tissue culture
(micropropagation). This study showed that all the tested forms of Beta
vulgaris produced large numbers of regenerants under tissue culture
conditions.
Beetroot could be genetically engineered for
herbicide-resistant or for resistance to viral pathogens in the same way as
sugar beet. However, it is unlikely that such modifications can be justified
in commercial terms. Modifications relating to colour or to root components
having medicinal properties are more likely goals. Variations in beetroot
pigments, specifically the betalains that give the roots their distinctive
red colour, have been studied using clonal material obtained by tissue culture.
Girod and Zryd demonstrated the importance of light, for instance, in the
induction of betalain synthesis using beetroot cell cultures. It may soon be
possible to manipulate betalain pigments in beetroot to influence root colour
or to make the pigments more stable. This could be done to improve their
value as a source of natural food colouring.
However, beetroot is a rustic crop, on the
fringes of agribusiness. It is not a natural designer crop. The market for
beetroot is small compared to most of the crops that have been genetically
modified. These crops have tended to be commodity crops that are heavily
processed, whereas beetroot is usually just boiled and pickled when
processed. Beetroot also has relatively few pest and disease problems, and is
easy to cultivate organically without pesticides. The main problem that has
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© Copyright Stephen Nottingham, 2004
sf.nottingham@btinternet.com
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