Biomedical Engineering Reference
In-Depth Information
Ayyangar [
35
] suggested that a single dominant gene confers the non-sweet
character. Later, it was reported that stalk sugar is under the control of recessive
genes with additive and dominance effects [
36
]. On the contrary, subsequent studies
provided support for the existence of multiple genes with additive effects. Contin-
uous variation in the amount of extractable juice was observed in juicy genotypes
and inbred progeny of juicy
dry lines, suggesting multiple genes may be involved
in controlling the trait [
8
,
37
,
38
]. There was also a report suggesting the involve-
ment of several genes affecting the biofuel traits in sweet sorghum background. The
evaluation of four promising sweet sorghum lines [Keller, BJ 248, Wray, and NSSH
104 (CSH 22SS) along with the check SSV 84] indicated substantial genotypic
differences for extractable juice, total sugar content, fermentation efficiency, and
alcohol production [
39
]. An analysis of 53 ICRISAT-bred elite hybrids in both the
rainy and post-rainy seasons showed that the correlation and regression coefficients
are significantly high for all the component traits of sugar yield (Brix%, stalk yield,
juice weight, and juice volume) [
2
]. Knowing general (GCA) and specific (SCA)
combining ability effects of genetic materials is of practical value in breeding
programs. GCA effects represent the fixable component of genetic variance and
are important to develop superior genotypes. SCA represents the non-fixable
component of genetic variation, and it is important to provide information on hybrid
performance. The line
tester analysis of 171 hybrids along with their parents in
both rainy and post-rainy seasons showed that the magnitude of SCA variance was
higher suggesting the importance of nonadditive gene action in inheritance of sugar
yield-related traits though both additive and dominant genes controlled overall
sugar yield during both rainy and post-rainy seasons in tropical sweet sorghums.
Hence, selection in early generations would be ineffective and recurrent selection
with periodic intercrossing is advocated. However, breeding for good combining
restorer parents can produce high sugar yields in post-rainy season. There is an
indication of existence of transgressive segregation for sugar yield that can be
exploited [
39
]. The heritability for traits such as stem juice content, stem sugar
concentration, total stem sugars, juice glucose, juice fructose, and juice sucrose was
low [
40
,
41
]. The predominant role of nonadditive gene action for plant height, stem
girth, total soluble solids, millable stalk yield, and extractable juice yield and
substantial magnitude of standard heterosis for candidate sugar traits (stem girth:
up to 5.3 %, total soluble solids%: up to 7.4 %, millable stalk yield: up to 1.5 %, and
extractable juice yield: up to 122.6 %) indicate the importance of heterosis breeding
for improving ethanol productivity of cultivars [
42
]. The significant positive cor-
relation of general combining ability (GCA) effects with per se performance of
parents in sweet sorghum facilitates quicker identification and development of
sugar rich, high biomass yielding hybrid parents [
2
,
43
]. The generation mean
analysis of two crosses has shown predominantly additive gene action for traits
like sucrose% and Brix% of juice. However, for cane and juice yield, dominance
gene action and dominance
dominance gene interaction were of higher magni-
tude in both the crosses. Since the traits important for high sugar content have
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