Biomedical Engineering Reference
In-Depth Information
Backcross Method
This method does not offer an opportunity to provide new recombinants as hybrids
are crossed back to either of the parents and thus they cannot be fixed. However, it
can be utilized to incorporate brown-midrib (
bmr
) or specific defense-related alleles
(e.g., stem borer resistance) or improve other traits like seed size, seed shape, and
cold tolerance through repeated backcrosses. The backcross method has also been
successfully employed in the Indian and ICRISAT breeding programs for transfer
of BMR genes and genes which confer high digestibility into elite dual-purpose
varieties. Several
bmr
lines in sweet sorghum background, stacked
bmr
mutants,
stem borer tolerant lines, etc. have been developed through this method. Several
stay-green QTLs (
stgB, stg2
,
and stg3
) are being introgressed into elite sweet
sorghum cultivars by deploying this method.
Population Improvement
This method provides long-term breeding strategy to derive diverse and broad
genetic-based superior varieties/hybrid parents. Therefore, a comprehensive crop
improvement strategy has to combine both short- and long-term progress for contin-
uous improvement of economic traits. The population improvement procedure
involves selection of component parents with high GCA, incorporation of genetic
male sterility, intercrossing and random mating among parents, and applying appro-
priate recurrent selection schemes. At ICRISAT-Patancheru, 24 sorghum populations
encompassing characters like grain mold, good grain, photo-insensitive, and early
dual purpose were developed and maintained. Recently, ICRISAT has started devel-
oping sweet sorghum population with
ms
3
gene for applying recurrent selection.
While population improvement programs are not the most common in sweet sorghum
breeding, they are an important source of genetic variation and improved traits.
Genomics
The availability of genomic sequence for sorghum has made it possible to carry out
genome-wide analyses. Whereas earlier studies on simple sequence repeat (SSR)
marker development primarily utilized anonymous DNA fragments containing
SSRs isolated from genomic libraries, more recent studies have used computational
methods to detect SSRs in sequence data generated from genomic sequences pro-
jects. In the sorghum genome, a total of 109,039 tandem repeats were detected, of
which 15,194 were microsatellite (SSR) markers [
46
]. In a recent studies, several
major QTLs for grain and stem sugar composition and yield and their results
indicated that overall energy yields could be increased by concurrent improvement
for both sorghum grain and sugar traits [
37
,
40
,
41
]. Elucidating the genetic basis of
stem sugar and stem juice accumulation, modifying cell wall composition so that
sorghum biomass can be processed more efficiently, maximizing biomass yield for
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