Environmental Engineering Reference
In-Depth Information
2001), and up to 40% GLA increase in
B. juncea
transformed with
Pythium irregulare
Buis. delta-
6-desaturase gene (Hong et al. 2002); reduction (>3.4%) or elevation (up to 68%) of saturated FA
(C16:0, C18:0) in
Brassica
by altering the expression of acyl-acyl carrier protein (KAS), desaturase
and thioesterases (Facciotti et al. 1999; Dehesh 2004); production of super-high erucic acid (C22:1)
rapeseed with an approximately 10% increase in erucic acid levels in rapeseed plants transformed
with the yeast
FAE1
gene (Katavic et al. 2000); and a transcriptome/metabolome analysis of
B.
napus
prototypes revealing an increase in TAG (triacylglycerol) accumulation in transgenic DGAT1
(diacylglycerol transferase 1) plants (Sharma et al. 2008).
18.2.5 c
ultivar
d
EvElopmEnt
The widespread cultivation of Brassica oilseeds throughout the world as one of the three most
important sources of vegetable oils is a result of plant breeders' successes in developing adapted
cultivars with reduced levels of erucic acid in the oil and glucosinolates in the meal. The
B. napus
rapeseed cultivars developed before 1970 (Stefansson and Downey 1995) had high concentrations
of both erucic acid (>40%, C22:1) in the oil and glucosinolate (>100 μM/g air-dried meal), and
were considered potentially harmful for humans and animals (Eskin et al. 1996). However, the
status of
B. napus
cultivars changed when plant breeders successfully introduced low levels of
C22:1 from the
B. napus
forage cultivar Liho from Europe into adapted cultivars by backcrossing
(Stefansson et al. 1961; Stefansson and Downey 1995). This was followed by the release of the first
low erucic acid (<5%), high glucosinolate
B. napus
and
B. rapa
cultivars such as Oro, Zephyr and
Span (Stefansson and Downey 1995). Although these cultivars produced high quality edible oil,
the nutritional quality/value of the meal was limited by the high concentration of glucosinolates.
The discovery of a
B. napus
cultivar Broonowski in Poland with a low glucosinolate concentration
presented the opportunity to overcome this barrier. The breeders at the University of Manitoba
(Canada) released world's first
B. napus
cultivar (Tower) with low erucic acid (<5%) and low
glucosinolate (<30 μM/g ) concentration in 1974 (Stefansson and Downey 1995). Traditional
breeding was then used to transfer the double-low traits (low erucic acid and low glucosinolate)
to both
B. napus
and
B. rapa
genetic backgrounds and release hundreds of double-low (canola)
cultivars (McVetty et al. 2008).
Canola cultivars derived from
B. napus
and
B. rapa
are now defined as having <2% erucic
acid and <30 μM total glucosinolates per gram of oil-free meal at 8.5% moisture (http://www.
canola-council.org). According to The Canola Council of Canada new standards are being set for
Canadian canola cultivars which will require the cultivars to have less than 1% erucic acid and less
than 18 μM total glucosinolates, and triple low (<2% C:22:1, <30 micromoles glucosinolates, <2%
acid detergent lignin content) canola cultivars are also a future goal for canola breeders. The canola
standard was extended to
B. juncea
in the early 2000 to develop canola quality mustard and the
first Canadian
B. juncea
canola commercial cultivars (Arid and Amulet) were released in 2002
in Canada although development of canola quality
B. juncea
started in Australia as early as 1981
(http://www.canola-council.org). Polyunsaturated FA (C18:2, C18:3) are nutritionally beneficial
for human health, but studies have shown that reducing the linolenic acid (C18:3) concentration
in canola from 10% to 3% can improve the canola oil stability, leading to a longer shelf life
(Tanhuanpaa and Schulman 2002). Similarly, it is known that oils with a high oleic acid (C18:1)
and low linoleic acid (C18:3) combination show higher oxidative stability at high temperatures
and thus produce less undesirable products during deep frying (Fitzpatrick and Scarth 1998).
Efforts to develop high-oleic-low-linolenic acid canola cultivars led to the release of world's first
low linolenic acid (>3%) cultivar “Stellar” by the University of Manitoba in 1987 (Scarth et al.
1987). The commercial cultivation of Stellar and other low-linolenic canola cultivars (Apollo and
Allons) remained limited due to their less than satisfactory agronomic performance (Stefansson
and Downey 1995; Scarth et al. 1997). The development of agronomically desirable double-low
canola cultivars with very high oleic acid (70-90%) and reduced linolenic (<3%) concentrations