Environmental Engineering Reference
In-Depth Information
of this crop is that it is relatively undomesticated, so yields are typically low. Improvements in seed
yield and oil percentage and quality are needed for a jatropha-based fuel industry to be successful.
At current yield levels, Lam et al. (2009) found that biodiesel production from Jatropha would not
be economically or environmentally competitive with oil palm (
Elaeis
guineensis
Jacq.) biodiesel
in Malaysia. As a relatively new crop, limited knowledge of genetic potential pertaining to specific
traits is a major hurdle in genetic improvement. Additionally, little is known of the naturally occur-
ring genetic diversity of the crop. Several studies using molecular markers have been conducted to
assess this diversity. Because little a priori knowledge of genomic sequences exists for this crop,
markers such as random amplified polymorphic DNA (RAPD; Kumar et al. 2009b; Ikbal et al.
2010), intersimple sequence repeat (ISSR; Kumar et al. 2009a), and AFLP (Tatikonda et al. 2009)
are well suited to these analyses. Ikbal et al. (2010) found moderate diversity among 40 Indian
J.
curcas
accessions (average similarity coefficient of 0.73, with a range of 0.44-0.92) using RAPD
markers. Kumar et al. (2009a) used ISSR markers to estimate genetic variation between
J. curcas
accessions and related
Jatropha
species; genetic similarity ranged from 0.346 to 0.807. Tatikonda
et al. (2009) genotyped 48 accessions collected from various locations in India using AFLP mark-
ers. Using principal component analysis (PCA) based on 680 polymorphic markers, they identified
five major groups. The genetic diversity did not appear to correlate with oil content or seed weight,
indicating multiple sources of variation for desirable traits.
Some SSR markers have been developed recently for jatropha (Pamidimarri et al. 2009), and
these will be useful for further diversity analyses, for creating a genetic map for this species, and
eventually for marker-assisted breeding and selection. Although jatropha is being developed as a fuel
crop, reduced toxicity is desirable for the purpose of utilizing the leftover seed meal as high-protein
animal feed. By screening a collection of 72 accessions representing germplasm from 13 countries
with RAPD and ISSR markers, Basha et al. (2009) identified several markers that appeared to be
associated with a reduced toxicity trait found in some Mexican
J. curcas
accessions. Some of these
markers were converted to more robust sequence-characterized amplified region (SCAR) markers
for use in MAS, although more detailed linkage mapping analysis will be needed to verify their
utility. This study also revealed limited genetic variability among most of the cultivated jatropha
accessions from around the world, and identified Mexico as a possible center of origin.
Given the relatively narrow genetic base of cultivated
J. curcas
, improvement of the crop may be
facilitated by crossing with other
Jatropha
species. Desirable traits such as photoperiod insensitivity,
stress tolerance, and oil quality, to name just a few, have been identified in related
Jatropha
species
(Basha and Sujatha 2009). Parthiban et al. (2009) reported high levels of incompatibility between
Jatropha
species, whereas Basha and Sujatha (2009) were able to create F
1
hybrids between
J. curcas
and several other
Jatropha
species by simple cross-pollination. Although self-compatible,
J. curcas
is
monoecious (Divakara et al. 2010), which facilitates cross-pollination. Successful crosses were veri-
fied by genotyping the progeny with parent-specific markers. Pollen fertility in the hybrids ranged
from 42 to 69%, suggesting that further crossing would be possible. Additionally, a hybrid between
J. curcas
and
J. integerrima
was successfully advanced to the F
2
and reciprocal backcross generations,
and significant phenotypic variation was observed. Recently completion of the first genomic sequence
for
J. curcas
was reported (Synthetic Genomics, Inc., 2009), resulting from a private venture between
Synthetic Genomics, Inc. and the Asiatic Center for Genome Technology. This should accelerate the
development of genetic markers and the directed integration of desirable genes for improvement of
jatropha as a biofuel crop.
1.3 the Present and near Future—cellulosIc ethanol From
croP resIdues and second-GeneratIon BIoFuel croPs
Use of food crops for producing fuel is relatively inefficient because only a small portion of the total
plant, and thus of the total captured solar energy, is utilized. The term “second-generation biofuels”
