Agriculture Reference
In-Depth Information
results improving cell wall digestion in tall
fescue (Buanai na
et al
., 2010) or Italian
ryegrass (
Lolium multil orum
) (Buanai na
et
al
., 2006).
After lucerne, maize is the second plant
that concentrates research ef orts aiming at
improving its digestibility, notably because
of the growing demand of the biofuel
industry; even so, it also has interest for
forage use. Advanced research is currently
being conducted in Spain to improve the
nutritional value of maize using the CAD
downregulation of lignin biosynthesis. Field
trials have proven that this approach is
suitable to improve the digestibility of
maize, as well as its energetic value for
biomass production (Fornalé
et al
., 2012).
Other teams in France and in North America
are also undertaking research to improve the
nutritive value of maize (Piquemal
et al
.,
2002; He
et al
., 2003) or sorghum (Funnell
and Pedersen, 2006). Interestingly, early
research has also been conducted in order to
improve the digestibility of rice, with
promising results (Zhang
et al
., 2006). Rice
is an important staple crop and its
by-products are used extensively for animal
feed, although the lignin content of the
stems is a limiting factor of this application.
Despite these limitations, one low lignin
event has reached the regulatory pipeline
and others will probably follow. h e lucerne
event, KK 179-5, should be ready for
commercialization before 2017. h e
potential for improved forage is very high.
In the EU-27, maize used as fodder was
covering 4.8 million hectares (Mha) in 2007,
representing about 37% of the total maize
area (Eurostat, 2013). Other forage plants -
temporary grasses, sorghum and legume
crops - occupy an additional 13.9 Mha,
which represents, together with the silage
maize area, about 11% of the EU-27 utilized
agricultural area. Moreover, the forage plant
area is likely to increase due to the steady
growth of the world's demand for meat.
Low-lignin plants would bring dif erent
kinds of benei ts to world agriculture. h ey
would contribute to the elevation of the
productivity of meat and dairy farms. It has
been estimated that a 1% increase in forage
digestibility would result in a 3.2% increase
in the daily weight gain of beef cattle (Casler
and Vogel, 1999). For the US dairy industry
as a whole, a 10% increase in cell wall
digestibility would generate additional meat
and milk sales of about US$380 million
yearly, decrease manure production by
2.3 Mt and reduce the needs for grain
complementation of rations of about 3 Mt
(Hati eld
et al
., 1999).
For forage crops such as lucerne, a low-
lignin variety would also allow farmers to
get higher yield with the same forage quality,
and at a cheaper production cost. Indeed,
i eld trials have shown that low-lignin
varieties of lucerne grown under a three-cut
system (i.e. involving three cuttings of
lucerne in one crop season) produce a higher
amount of forage than conventional
varieties grown under a four-cut system,
since the forage can be harvested later when
the plant is mature and has the highest
growth without suf ering loss of quality
(Undersander, 2010). Last, but not least,
low-lignin maize, switchgrass or tall fescue
have huge potential benei ts for bioethanol
production. It has been reported that a low-
lignin maize line would increase bioethanol
production by up to 51% per unit of land
compared to a conventional maize (Fornalé
Prospects and challenges for commercial
use of low-lignin plants
h e breeding of GM plants featuring a low
lignin content suitable for commercial-
ization is facing a number of limitations,
which are linked principally to the role that
lignin plays in other plant physiological
pathways (Zhao and Dixon, 2011; Jung
et
al
., 2012). First, lignin inl uences plant
i tness, through its ef ect on vigour, on
susceptibility to lodging and to disease, on
drought tolerance and on productivity.
Plants with severe reduction in the lignin
content also tend to dwarf. Second,
knowledge of the regulation of the genes
involved in the biosynthesis of lignin, and
more generally in cell wall biosynthesis, still
has to be improved. Finally, even the nature
of the relationship between cell wall
composition and forage digestibility is still
incompletely known.
