Agriculture Reference
In-Depth Information
content was reduced. h e content of total
alkaloids in transgenic potatoes has been
increased and needs further research
(Böhme
et al
., 2005).
Lignin does not belong to the group of
carbohydrates, but it is an important
ingredient of most i bre fractions of plant
cell walls. Lignin is also considered to be an
undesirable constituent of feed. Lignin and
i bre fractions (e.g. NDF, ADF, crude i bre)
are very important for the digestibility and
feed value of the vegetative parts of plants,
as well as the performance of ruminants. A
reduction of lignin or a less intensive
connection between lignin and cellulose/
hemicellulose may contribute substantially
to a higher digestibility and a higher dry
matter intake of many roughages. So-called
brown midrib (bm) hybrids (e.g. maize,
sorghum), as a result of traditional mutation
breeding (Cherney
et al
., 1991; Grant
et al
.,
1995; Taylor and Allen, 2005a,b), demon-
strate the inl uence on digestibility (Rook
et
al
., 1977; Koehler
et al
., 1989; Ivan
et al
.,
2005; Gorniak
et al
., 2012) and rumen
fermentation, feed intake and the per-
formance of ruminants (Oba and Allen,
1999, 2000a,b; Barriere
et al
., 2004; Ivan
et
al
., 2005).
Based on these data, genetic engineering
may also be helpful to increase feed value
and feed intake of low-quality roughages.
Such studies may also contribute to
increasing the feed value of some co-
products, e.g. straw from grain production.
On the other hand, lignin is a very important
ingredient for cell wall stability, and
therefore for the steadiness of the stalks of
cereals and maize. h e propensity for layers
of such plants including bm hybrids is higher
than for plants with higher lignin content.
terms of micronutrients (minerals and
vitamins; Welch and Graham, 2004).
h erefore, the supplementation of nutrition
with minerals is necessary and usual.
In some regions, it is dii cult to
supplement human diets with minerals, and
often mineral supplements such as lick
stones or other mixtures are not available in
adequate composition and amounts for
animals. h erefore, biofortifying of crops
with essential mineral elements (e.g. Fe, Zn,
Ca, Zn, Se, etc.) and increasing the bio-
availability of minerals may contribute
towards overcoming the gap between feed/
food content and requirements for animals/
humans (Welch and Graham, 2004; White
and Broadley, 2005). During the past few
years, plant breeding has made progress by
using biotechnological tools to increase the
pace and prospects for success of the
biofortii cation of many plants with
minerals, especially for staple food crops
such as rice, cassava, wheat, maize and beans
(Gregorio, 2002; Holm
et al
., 2002). Special
attention has been paid to iron and zinc,
because iron dei ciency is estimated to af ect
about 30% of the world population (WHO,
2008; Lynch, 2011). Plant breeding might
provide a sustainable and cost-ef ective
solution in the long run, delivering minerals
to the entire population (White and
Broadley, 2005; see also Chapter 12). Two
approaches have been used to improve the
mineral content in feed/food (Frossard
et al
.,
2000; Colangelo and Guerinot, 2006):
1.
To increase the ei ciency of uptake and
transport of minerals into edible plant
tissues.
2.
To increase the amount of bioavailable
mineral accumulation in the plant.
h ere are various studies to test the mineral
bioavailability in model animals as shown
for iron (see Tako
et al
., 2010):
Humans and animals require about 20 major
and trace elements (see Table 7.1). h e
normal animal diet consisting of forage/
roughage and concentrates or co-products
from concentrates does not meet the
nutritional requirements of animals. About
three billion people are malnourished in
Fe and Zn in genetically enriched beans
and rice (Welch
et al
., 2000; Welch, 2002;
Tako
et al
., 2009).
Fe in genetically modii ed grains expres-
sing a microbial phytase or reduced level
of phytate (Holm
et al
., 2002; Sautter
et
al
., 2006).
