Sweet Sorghum: Breeding and Bioproducts - Industrial Crops: Breeding for BioEnergy and Bioproducts - page 3

to grain sorghum types, while sweet sorghum varieties had 54 % higher sugar yield
and 9 % lower grain yield compared to non-sweet stalk varieties in the rainy season.
On the other hand, both sweet sorghum hybrids and varieties had higher stalk sugar
yields (50 and 89 %) and lower grain yields (25 and 2 %) in the post-rainy season.
Thus, there is little trade-off between grain and stalk sugar yields in the sweet
sorghum hybrids in the rainy season, while the trade-off is less in varieties in the
post-rainy season [ 2 , 3 ].
This is further corroborated by other published work [ 11 ] showing that there is
significant soluble sugar content in the stems (79-94 %) during post-anthesis
period, with the hybrids exhibiting significantly high soluble sugar content over
varieties with same maturity period and effects of year, harvest time, and genotype
on calculated ethanol yield (CEY) are highly significant. The experimental data on
the relationship between stalk sugar traits and grain yield shows that the regression
coefficient of stalk sugar yield on grain yield is not significant, thereby indicating
that the grain yield is not affected when selection is done for stalk sugar yield.
Hence, selection programs can aim to improve both the traits simultaneously.
Climate Change
Global warming due to climate change will affect grain and stover yields in crops,
more so in tropical Africa and Asia where sorghum is a major food crop. Most
climate change models predict rise in air and soil temperatures and sea levels and
increased frequencies of extreme weather events leading to unprecedented changes
in agricultural production in the years to come. In the Intergovernmental Panel on
Climate Change (IPCC), climate models predict an increase in global average
surface temperature of between 1.4 and 5.8 C from 2001 to 2100, the range
depending largely on the scale of fossil fuel burning between now and then and
on the different models used. At the lower range of temperature rise (1-3 C),
global food production might actually increase, but above this range, it would
probably decrease [ 12 ]. However, broad trends will be overshadowed by local
differences, as the impacts of climate change are likely to be highly spatially
variable. In general, the sorghum maturity period of current varieties decreases
with increased temperatures. Climate change effects in terms of high temperatures
and erratic rainfall may drastically reduce sorghum yields in South Asia, Southern
Africa, and West Africa [ 13 ]. Climate change will cause changes in the length of
the growing period (LGP) in some regions. Cooper et al. [ 13 ] showed that the extent
of global semiarid tropical (SAT) areas will be changed through (1) SAT areas
being “lost” from their driest margins and become arid zones due to LGPs becom-
ing too short or (2) SAT areas being “gained” on their wetter margins from