Biomedical Engineering Reference
In-Depth Information
architecture, abiotic stress tolerance, and seed-oil characteristics. Diseases and
insects have not been in issue in the crop as no major incidence related to these
has been observed during limited trials. The agronomic performance of lesquerella
was found not to be affected by the predominant insect pest,
Lygus
sp., in the
southwest United States, but additional studies are needed to be done when the crop
is grown under commercial cultivation [
77
,
78
].
The reestablished lesquerella breeding program has contributed significantly in
improving the seed-oil content of the crop. Dierig and Ray [
79
] reviewed that
improved germplasm has an oil yield advantage of 60 l/ha over unimproved
germplasm materials. When translated into seed-oil content, this is equivalent to
an increase of 8-12 % in the improved germplasm. The latest lesquerella lines that
were developed have more than 33 % seed oil and a harvest index of up to 16.5,
significantly higher and a tremendous improvement compared to 0.14 harvest index
observed in unimproved germplasm [
80
]. Selection for materials with increased
lesquerolic acid has also been successful with the release of WCL-LH1 having
about 8.6 % increase in lesquerolic acid content in the seed oil [
70
]. A salt-tolerant
germplasm, WCL-SL1, was later developed using plants that survived high salinity
levels (21 and 24 dS m
1
electrical conductivities) as parental materials [
81
].
P. fendleri
is a diploid (2
x
12). Other species have different chromosome
numbers ranging from 8 to 40 [
35
]. The feasibility of interspecific hybridization has
been demonstrated as possible using
P. fendleri
,
P. pallida
, and
P. lindheimeri
[
27
]. Interspecific hybridization is being explored as a possible strategy to further
improve the HFA content of
P. fendleri
which is relatively low (~50 %) compared
to the two other mentioned species (both with
¼
2
n
¼
80 %) [
63
]. Interspecific hybrids
were observed to have elevated content of HFA (~70 %) indicating the possibility
of increasing the crop's oil content by genetic introgression specifically from the
endangered species
P. pallida
[
82
]. Previous reports on lesquerella species with
natural habitats in the western United States however indicated that natural hybrid-
ization among them is not common. It is the opposite for species found in the
eastern United States [
83
-
85
]. Additional research to evaluate interspecific hybrids
in
Physaria
is needed.
>
Breeding Methods and Integration of New Biotechnologies
Breeding Methods
The research activities at USDA included development of genetic stocks with
improved traits for direct utilization or for use as base materials to develop new
lines. Thompson and Dierig [
69
] outlined the methodologies used to develop
different lesquerella breeding populations. The specific approach included using
single-plant selections from the unimproved accessions, bulking selections from
half-sib families to develop the lesquerella Texas and Arizona subpopulations
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