Environmental Engineering Reference
In-Depth Information
also transferrable (75% of primer pairs tested). Polymorphisms were detected among 11 miscanthus
accessions using some of the maize-derived SSR markers. Such markers could be added to the
M. sinensis
map, and it may be possible to correlate known QTL positions in other grass genomes
with those in
M. sinensis
.
Napiergrass, also known as elephantgrass, has been developed primarily as a forage species
for the tropics. Because forage is harvested while the growth is still quite young and digestible, it
has high protein content and has a greater proportion of biomass in the leaves. Dwarf leafy types,
such as the cultivar 'Mott' (Sollenberger et al. 1989), have been developed specifically as high-
quality forage varieties. For bioenergy production, the opposite plant type is desired: tall plants
with most of the biomass in the stems. The cultivar 'Merkeron' was also developed initially as a
high-yielding forage cultivar, but it is capable of reaching a height of 4 m, with a considerable per-
centage of stem biomass. Even under low fertility, substantial yields are possible. With no added
fertilizer, 'Merkeron' yielded over 25 Mg ha
-1
yr
-1
dry matter for the first two seasons at Tifton, GA,
although yields declined without additional fertilization in subsequent seasons (Knoll et al. 2011).
'Merkeron' was selected from a cross between a leafy dwarf type and a tall type (Burton 1989),
and selfed populations of progeny from 'Merkeron' segregate for the dwarf characteristic. In addi-
tion to 'Merkeron,' several other promising napiergrass selections are being evaluated at Tifton,
GA, and other locations in the southeastern United States for their potential as biomass feedstocks.
Important traits include biomass yield, cold tolerance and overwintering ability, nitrogen use effi-
ciency, and improved biomass digestibility for cellulosic ethanol conversion.
A few investigations of genetic diversity in napiergrass have been conducted. Isozymes, iso-
electric or molecular size variations in specific proteins, have been used successfully to fingerprint
napiergrass accessions and evaluate their diversity (Daher et al. 1997; Bhandari et al. 2006). More
recently, Pereira et al. (2008) surveyed the diversity in a Brazilian collection of 30 napiergrass
accessions using RAPD markers. Twenty primers were tested, which yielded 88 scorable bands, of
which 64 showed polymorphism among the accessions. Moderate genetic diversity (average genetic
distance 0.21, maximum 0.34) was revealed, along with several possible duplicated accessions. Babu
et al. (2009) also used DNA markers (RAPD and ISSR) to survey genetic diversity among a large
collection of napiergrass accessions. Interestingly, the data from the two different marker systems
generated different dendrograms, although both data sets showed correlation with geographic ori-
gins of the accessions. AFLP markers have also been applied to assess diversity among napiergrass
accessions (Anderson et al. 2008). SSR markers have been developed for the related species pearl
millet
[
Pennisetum glaucum
(L) R. Br.; Senthilvel et al. 2008], and it is likely that some of these
could be used in diversity assessments, genetic mapping, and eventually marker-assisted breeding
in napiergrass.
Napiergrass is protogynous, so crossing is facilitated by pollination before the anthers emerge,
although selfing is also possible (Hanna et al. 2004). The breeding scheme for napiergrass is similar
to that for other clonally propagated species. F
1
hybrids are generally heterogeneous, and single-
plant selections are increased by stem cuttings, in a similar manner as for sugarcane, for further
testing. Napiergrass can also be successfully crossed with pearl millet; the resulting plant was called
“elephantmillet” by Woodard and Prine (1993). Napiergrass is allotetraploid, and crosses with pearl
millet result in triploid offspring which are sterile, although fertile hexaploids can be recovered
through chromosome doubling with colchicine (Hanna 1981; Anderson et al. 2008). Napiergrass
has also been successfully crossed with an apomictic relative
P. squamulatum
; the hybrid has some
fertility (Hanna et al. 2004; Anderson et al. 2008). The apomictic trait in
P. squamulatum
is carried
on a hemizygous chromosome segment, termed the apospory-specific genomic region (ASGR; Goel
et al. 2003). Although the underlying genetic mechanism is still unclear, molecular markers located
on the ASGR should facilitate selection for the trait. Several backcrosses could result in an apomic-
tic napiergrass, which would have the advantages of seed propagation while maintaining hybrid
vigor and the uniformity of vegetatively propagated material. Seed production would be limited to
tropical and subtropical areas because flowering in napiergrass is short-day sensitive.
