sugar tech paper

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Sugar TechAn International Journal of Sugar Cropsand Related Industries ISSN 0972-1525Volume 14Number 3 Sugar Tech (2012) 14:237-246DOI 10.1007/s12355-012-0166-9

Combining Ability and Heterosis overEnvironments for Stalk and Sugar RelatedTraits in Sweet Sorghum (Sorghum bicolor(L.) Moench.)

A. V. Umakanth, J. V. Patil, Ch. Rani,S. R. Gadakh, S. Siva Kumar, S. S. Rao &Tanmay Vilol Kotasthane

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RESEARCH ARTICLE

Combining Ability and Heterosis over Environments for Stalkand Sugar Related Traits in Sweet Sorghum (Sorghum bicolor (L.)Moench.)

A. V. Umakanth • J. V. Patil • Ch. Rani •

S. R. Gadakh • S. Siva Kumar • S. S. Rao •

Tanmay Vilol Kotasthane

Received: 18 January 2012 / Accepted: 1 June 2012 / Published online: 22 June 2012

� Society for Sugar Research & Promotion 2012

Abstract Till date only one sweet sorghum hybrid CSH

22SS has been released for general cultivation in India and

the current levels of new hybrids are unable to surpass this

hybrid. The objective of this study was to assess the general

and specific combining abilities of eight parents and 16

hybrids respectively at three semi arid locations by following

a line 9 tester mating design. Significant differences among

environments, testers, environments 9 testers and environ-

ments 9 line 9 tester effects were observed for all traits

suggesting the environmental influence on testers and the

interactions. The variance component estimates of specific

combining ability (SCA) were greater than that of general

combining ability (GCA) for total biomass, juice extraction

and grain yield indicating the non-additive control of genetic

variation while the GCA variance was higher than the SCA

variance for fresh stalk yield, juice yield, brix content, total

sugar yield and computed bioethanol yields indicating

additive gene action. Among females, DMS 28A for fresh

stalk, juice and grain yields and DMS 25A for brix content

were promising. Rio was a potential male parent for fresh

stalk yield, total sugar content, computed bioethanol and

grain yields. These parents can be exploited to address eth-

anol production from juice without compromising on grain

yields. The best hybrids for total biomass, fresh stalk yield,

juice yield, juice extraction, total sugar content and com-

puted bioethanol yields were DMS 13A 9 Rio and DMS

23A 9 RS 647 and after adequate testing across many

locations, these hybrids are recommended for commercial

exploitation for ethanol production.

Keywords Sweet sorghum � Biomass � Brix �Combining ability � Ethanol

Introduction

Sorghum [Sorghum bicolor (L.) Moench] is the fifth major

cereal crop in the world and is the principal dry land coarse

cereal grown in semi-arid environments of India covering an

area of 7.53 million hectares, with a production of

7.25 million tons at a productivity of 962 kg/ha (Anony-

mous 2011). In the form of sweet sorghum, it has the capa-

bility to influence and improve the rural livelihoods in India

due to its potential industrial use for bioethanol production.

The national biofuel policy of 2009 aims at promoting bio-

fuels to meet India’s energy needs in an environmentally-

sustainable manner, while reducing its import dependence

on fossil fuels. The policy also proposed an indicative target

of 20 per cent blending of ethanol by 2017 from the current

10 per cent ethanol blending with petrol. The traditional

route of ethanol production through sugarcane molasses

would not be meeting this huge demand because of the dif-

ficulties in increasing the sugarcane area beyond the current

4.4 million ha in the country. Therefore, renewable sources

of energy in the form of other biofuel crops would be

promising options in view of the emerging trends in inter-

national energy markets as well as indigenous strengths.

Sweet sorghum has been used for nearly 150 years to pro-

duce concentrated syrup with a distinctive flavor (Schaffert

A. V. Umakanth (&) � J. V. Patil � Ch. Rani �S. S. Rao � T. V. Kotasthane

Directorate of Sorghum Research, Rajendranagar, Hyderabad

500030, Andhra Pradesh, India

e-mail: [email protected]

S. R. Gadakh

Sorghum Research Station, MPKV, Rahuri, Maharashtra, India

S. Siva Kumar

Department of Millets, TNAU, Coimbatore, Tamil Nadu, India

123

Sugar Tech (July-September 2012) 14(3):237–246

DOI 10.1007/s12355-012-0166-9

Author's personal copy

1992). The stem juice of sweet sorghum is rich in fermen-

tative sugar and is a desirable material for alcoholic fer-

mentation. Further, the stillage from sweet sorghum after the

extraction of juice has higher biological value than the

bagasse from sugarcane when used as fodder for animals, as

it is rich in micronutrients and minerals. The sweet sorghum

bagasse is as good as the stover for the intake and body

weight gain in the animals when used as live-stock feed.

Apart from these, stillage contains similar levels of cellulose

as sugarcane bagasse, therefore has a good prospect as a raw

material for pulp product (Srinivasa Rao et al. 2009). The

bagasse or residue can also be used to cogenerate power of

about 3.2–3.4 MW/ha (Gururaj et al. 2010) for every hectare

of crop. Besides these uses, the whole plant biomass can also

be used as a substrate for production of ligno cellulosic

ethanol. Sweet sorghum was suggested as the best alternative

feedstock for bio ethanol production (Dayakar Rao et al.

2004; Shukla et al. 2006).

Sweet sorghum is the best alternative raw material to

supplement the use of sugarcane in ethanol production

according to a pilot study conducted by Vasantdada Sugar

Institute. At 5,600 l per hectare per year (from two crops,

at 70 tons per hectare of millable stalk per crop at 40 l per

ton), the ethanol production from sweet sorghum compares

well with the 6,500 l per ha per crop for sugarcane (at

85–90 tons per hectare of millable cane per crop at 75 l per

ton) (Anonymous 2004). Techno-economic feasibility

studies have shown that the cost of alcohol production from

sweet sorghum was Rs 1.87 less than that from molasses.

This conclusion was based on the prevailing prices of

molasses during that period. In addition to sweet stalk, an

average grain yield of 1.5–2.0 t/ha can be harvested which

can be used as food or feed (Dayakar Rao et al. 2004).

Concerted research efforts during last two decades at

Directorate of Sorghum Research and its cooperating centres

in different State Agricultural Universities under National

Agricultural Research System and at ICRISAT have resulted

in excellent sweet sorghum varieties for use in ethanol pro-

duction by the sugar industries/alcohol distilleries and for

use as green/dry fodder. However, till date only one sweet

sorghum hybrid CSH 22SS has been released (in the year

2005) for general cultivation in India and the current yield

levels of new hybrids are unable to surpass this hybrid. This

necessitates the identification of new hybrid parents with

good combining ability for different traits of interest.

In hybrid oriented breeding programmes, the knowledge

of combining ability of the parents and the inheritance of

the traits is important (Itai et al. 2010). This information

helps in optimizing the breeding strategy, either selection

when general combining ability (GCA) effects are impor-

tant; inbreeding followed by hybrid breeding when specific

combining ability (SCA) effects are predominant; or

selection followed by hybridization if both are important;

because GCA effects are attributed to preponderance of

genes with additive effects and SCA indicates predomi-

nance of genes with non-additive effects (Kenga et al.

2004; Mutengwa et al. 1999). Studies have shown both

GCA and SCA to be important in many sorghum traits

including grain yield (Haussmann et al. 1999; Tadesse

et al. 2008; Yu and Tuinstra 2001). The objective of this

study was to determine the combining ability of 8 parents

for stalk and sugar related traits. The study envisaged

assessing the general combining ability of parents and

specific combining ability of hybrids by following a

line 9 tester (L 9 T) mating design and the experiment

was conducted at 3 diverse locations as significant geno-

type 9 environment interaction effects have been reported

in sorghum (Chapman et al. 2000).

Materials and Methods

Plant Material

Four cytoplasmic genetic male sterile lines (DMS 13A, DMS

23A, DMS 25A and DMS 28A) used as females (A-lines)

were crossed on to each of the four male-fertile lines (N 98,

Rio, RSCN 5008 and RS 647) in line 9 tester fashion to

produce 16 F1 hybrids during post rainy season of 2009 at

Directorate of Sorghum Research (DSR), Hyderabad. The

males included two sweet stalked temperate lines (N 98 and

Rio) and two sub-tropical breeding derivatives (RSCN 5008

and RS 647) in sweet stalk background with high stalk yields

while the females had higher sugar content (Table 1). The

parental line selection criteria were based on characters

contributing to increased stalk and sugar yields.

Experimental Sites

The 16 F1 hybrids, their corresponding eight parents and

three checks were evaluated at three different locations in

three different states of India with semi-arid environments

viz., Directorate of Sorghum Research (DSR) farm, Hy-

derabad, Andhra Pradesh (latitude 17�190N, longitude

78�230E), Centre for Plant Breeding and Genetics farm,

Tamil Nadu Agricultural University, Coimbatore, Tamil

Nadu (latitude 11�00N, longitude 76�550E) and Sorghum

Research Station farm, Mahatma Phule Krishi Vidyapeeth,

Rahuri, Maharashtra (latitude 19�200N, longitude 74�380E)

during rainy season of 2010. The experiment was con-

ducted in a Randomized Block Design with three replica-

tions at all the three locations. Each entry was raised in two

rows of 4 m length with 60 9 15 cm spacing. Recom-

mended agronomic practices were followed throughout the

crop season. Atrazine (1.0 kg/ha of active ingredient) was

applied immediately after sowing. A basal fertilizer dose of

238 Sugar Tech (July-September 2012) 14(3):237–246

123


42 kg/ha N, 42 kg/ha P2O5 was applied just before sow-

ing, in the 2nd week of June 2010, and a topdressing of

46 kg/ha N was applied 1 month after germination (floral

initiation stage) in the third week of July 2010. In each rep-

lication, observations were recorded on 10 randomly selec-

ted competitive plants. At physiological maturity, data was

recorded on following traits.

Traits Studied

Total fresh biomass (t/ha): At physiological maturity, all

the plants in net plot with their leaves, stems, and panicles

were weighed in kilograms and then converted into tons

per hectare.

Fresh stalk yield (t/ha): The leaves plus sheath and pan-

icles were removed from the plants carefully and the weight

of the fresh (millable) stalk yield in the net plot was recorded

in kilograms and later converted into tons per hectare.

Juice yield: The extraction of juice from 10 randomly

selected plants was done on an electrically operated three-

roller stalk crusher with a minimum of three passings of the

fresh (millable) stalk so that the last drop of juice came out

from the stems. Juice extracted was measured in kilograms

and later converted into litres per hectare.

Brix content: It is a measure of the mass ratio of soluble

solids to water, is a widely used approximation for sugar

content and is reported as a trait in the rest of the text. The

brix values from the composite juice were recorded �brix,

using an Atago PAL-1 digital hand-held pocket refrac-

tometer (with automatic temperature compensation ranging

from 0 to 50 �C) at the hard dough stage.

Juice extraction (%): The juice extractability in percent

was calculated using the data of total weight of ten fresh

stalks

Juice extraction %ð Þ¼ Juice weight=Fresh stalk yieldð Þ½�100�:

Total Sugar yield (t/ha): Total sugar yield was calculated

on the basis of following formula (Reddy et al. 2005).

Total soluble sugar %ð Þ=100ð Þ � Juice yield kl=hað Þ

Grain yield: All the panicles were collected from the net

plot, threshed, dried and the dry weight was recorded in

kilograms at 14 % seed moisture content and later

converted into kilograms per hectare.

Computed ethanol yields: The ethanol yields were cal-

culated based on the total sugar yield (Smith and Buxton

1993).

Statistical Analysis

Analysis of variance for combining ability was carried out

using mean values across environments (Kempthorne 1957)

to test the significance of differences among the genotypes

including crosses and parents (Snedecor and Cocharan 1967;

Panse and Sakhatme 1964). The sum of squares for hybrids

was further partitioned into variation due to lines, testers and

line 9 tester interactions. The mean squares due to lines and

testers were tested against the mean squares due to

line 9 tester, and the latter were tested against the pooled

error. The mean squares due to environment 9 line and

environment 9 tester were tested against the mean squares

due to environment 9 tester 9 line, and the latter was tested

against the pooled error. Estimate of GCA variances

(r2 GCA) and SCA variances (r2 SCA) were obtained (Singh

and Chaudhary 1977). Mid-parent heterosis and better parent

heterosis were estimated and tested by working out the

standard errors (Hays et al. 1955).

Results

Combined analyses of variance for eight characters mea-

sured over three environments are presented in Table 2.

Significant differences among environments, testers, envi-

ronments 9 testers and environments 9 line 9 tester

effects were observed for all the characters studied sug-

gesting that the testers and the interactions for these traits

were influenced by the environment. The line 9 tester

Table 1 Details of parental sorghum lines used to generate 16 hybrids

Line no Name Fertility status Origin Role in crosses Principal selection criteria

1 DMS 13A CMS India Female High sugar, high stalk yield

2 DMS 23A CMS India Female High sugar, high stalk yield

3 DMS 25A CMS India Female High sugar

4 DMS 28A CMS India Female High sugar

5 N 98 CMF USA Male High sugar

6 Rio CMF USA Male High sugar, high stalk yield

7 RSCN 5008 CMF India Male High sugar, high stalk yield

8 RS 647 CMF India Male High sugar, high stalk yield

CMF cytoplasmic male fertile, CMS cytoplasmic male sterile

Sugar Tech (July-September 2012) 14(3):237–246 239

123


effect was also significant for all the traits except brix

content indicating the existence of genetic diversity in the

material tested. The line effects were non-significant for

total biomass while the environment 9 line effect was not

significant for total sugar content, grain yield and com-

puted bioethanol yields.

The importance of the source of variation is indicated by

the relative magnitude of variance components. The vari-

ance component estimates of SCA were greater than that of

GCA for total biomass, juice extraction and grain yield

(Table 3) indicating the non-additive control of genetic

variation for these traits. On the contrary, the GCA vari-

ance was higher than the SCA variance for fresh stalk

yield, juice yield, brix content, total sugar yield and com-

puted bioethanol yields indicating the presence of additive

gene action. In addition, the ratio of the mean square

components associated with variance of GCA and SCA

was in negative direction and much less than the theoretical

maximum of unity for most of the traits studied. There was

significant interaction of variance due to SCA with envi-

ronment for all the characters studied except juice extrac-

tion (%).

The selection of parental lines for hybrid programs was

the main objectives of this study. Thus, the estimates of the

general combining ability (gi) of a parent provide impor-

tant indicators of its potential for generating superior lines.

A low gi estimate, whether positive or negative, indicates

that the mean of a parent in crossing with the other, does

not differ greatly from the general mean of the crosses. On

the other hand, a high gi estimate indicates that the parental

mean is superior or inferior to the general mean (Kenga

et al. 2004).

Estimates of GCA effects for different traits viz., total

biomass, fresh stalk yield, juice yield, brix content, juice

extraction, total sugar content, grain yield and computed

bioethanol yields for the eight parents used in this study are

presented in Table 4. DMS 28A was the most promising

female parent for most of the traits like fresh stalk yield,

juice yield, juice extraction and grain yield with highly

significant and positive GCA effects but the GCA effects

for brix content were in the negative direction. The female

DMS 23A was the best general combiner for total biomass

while DMS 25 A was good general combiner for total

biomass, brix content and juice extraction. On the other

hand, the female DMS 13A showed significant and nega-

tive GCA effects for total biomass, juice yield, juice

extraction and grain yield.

Among the male parents (testers), N 98 was the best

general combiner for juice extraction. However it was not a

good combiner for total biomass, fresh stalk and grain

yields. Rio was the best combiner for most of the important

traits related to biofuel production like fresh stalk yield,

brix content, total sugar content, grain yield and computedTa

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123


bioethanol yields. The testers RSCN 5008 and RS 647 were

promising for total biomass only.

It was observed that on a pooled basis, significant and

positive SCA effects for total biomass were shown by 5

hybrids viz., DMS 23A 9 RS 647, DMS 13A 9 Rio, DMS

13A 9 RSCN 5008, DMS 25A 9 N 98 and DMS

25A 9 Rio. These hybrids showing significant and positive

SCA effects were also among the best in per se perfor-

mance (Table 5). With respect to fresh stalk yield, DMS

13A 9 Rio and DMS 23A 9 RS 647 exhibited significant

and positive SCA effects and the trend in per se perfor-

mance was similar to total biomass. However, the hybrid

DMS 28A 9 Rio which was the top fresh stalk yielder

showed insignificant negative effects. For juice yield, the

hybrid DMS13A 9 Rio recorded significant and positive

SCA effects and it also excelled in biomass traits too. DMS

28A 9 Rio and DMS 28A 9 RSCN 5008 were the other

hybrids with high mean juice yields but insignificant and

positive SCA effects. Out of 16 hybrids, only one hybrid

DMS 13A 9 RSCN 5008 demonstrated significant and

positive SCA effect for brix content. DMS 25A 9 Rio

recorded the highest brix content in the trial but had shown

a non-significant SCA effect which was in the positive

direction. Six hybrids viz., DMS 23A 9 N 98, DMS

25A 9 RSCN 5008, DMS 28A 9 N 98, DMS 13A 9 Rio,

DMS 25A 9 Rio and DMS 25A 9 RS 647 showed

desirable SCA effects for juice extraction. All these six

hybrids recorded higher juice yields. However it was

gratifying to note that three hybrids exhibited positive SCA

effects while the other three have shown negative SCA

effects for juice yields which were non-significant. For

total sugar content, the hybrids DMS 13A 9 Rio and DMS

Table 3 Estimates of variance components as reference to the prevailing gene action

Source Total

biomass

(t/ha)

Fresh stalk

yield (t/ha)

Juice yield (l/ha) Brix

content

(%)

Juice

extraction

(%)

Total sugar

yield (t/ha)

Grain yield

(kg/ha)

Computed

ethanol

yields (l/ha)

r2 Environments 221.788** 94.873*** 9,905,079.170*** 13.693*** 34.368** 0.215*** 133,643.140 ** 60,204.159***

r2 gca -10.982 1.301 227,523.945 0.329 4.624 0.001 60,166.904 643.923

r2 sca 15.469 -3.412 -1,137,624.929 -0.736 10.283** -0.001 273,641.090 *** -1,291.342

r2 gca/r2 sca -0.709 -0.381 -0.200 -0.447 0.449 -1.666 0.219 -0.498

r2

gca 9 environments

50.998* -0.273 -305,541.301 -0.429 8.408 -0.000 9,403.367 -441.428

r2 sca 9 environments 66.718*** 45.969*** 5,083,964.079*** 2.985*** 10.092 0.090*** 84,664.377 * 26,077.082 ***

*, **, *** Significant at P B 0.05, 0.01 and 0.001, respectively

Table 4 Pooled estimates of general combining ability effects of parents in sweet sorghum

S. No. Parents Total

biomass (t/ha)

Fresh stalk

yield (t/ha)

Juice yield

(l/ha)

Brix

content (%)

Juice

extraction

(%)

Total sugar

yield (t/ha)

Grain yield

(kg/ha)

Computed ethanol

yields (l/ha)

Females

1. DMS 13A -5.278*** 0.035 -566.174* 0.092 -5.376*** -0.029 -414.896*** -16.333

2. DMS 23A 3.028*** -1.354* -421.229 -0.322 -0.234 -0.082* -157.785 -44.083*

3. DMS 25A 2.806*** -0.326 121.993 0.544* 3.858*** 0.043 104.521 20.278

4. DMS 28A -0.556 1.646** 865.410** -0.314 1.752*** 0.068 468.160*** 40.139

S.E (gi) 0.660 0.0531 262.498 0.239 0.268 0.039 85.568 20.352

S.E (gi-gj) 0.934 0.751 371.22 0.33 0.379 0.055 121.012 28.78

Males

1. N 98 -5.472*** -2.826 *** -861.104 0.328 3.722*** -0.043 -408.285*** -22.889

2. Rio -0.778 3.618*** 33.868 0.669 ** -1.481*** 0.188*** 454.882*** 95.278***

3. RSCN 5008 3.139*** -1.021 826.785 -0.119 -1.190*** -0.06 169.965 -28.667

4. RS 647 3.111*** 0.229 0.451 -0.878 *** -1.051*** -0.085* -216.563* -43.722*

S.E (gi) 0.660 0.053 262.498 0.239 0.268 0.039 85.568 20.352

S.E (gi-gj) 0.934 0.751 371.22 0.33 0.379 0.055 121.012 28.78

*, **, *** Significant at P B 0.05, 0.01 and 0.001, respectively


123


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5*

2,6

38

10

.44

45

02

2D

MS

13

A9

Rio

6.9

17

**

*4

13

.52

1*

**

28

1,1

32

.56

3*

9,6

17

.77

-0

.52

21

4.9

1.4

51

**

29

0.3

35

**

*1

.49

-8

44

.41

0*

**

2,2

52

17

1.1

67

**

*7

81

3D

MS

13

A9

RS

CN

50

08

6.6

11

**

*4

50

.16

02

5-

42

0.0

76

7,2

15

.33

1.0

11

*1

5.7

-1

.33

0*

26

-0

.08

50

.82

10

2.7

29

2,9

15

-3

8.0

00

44

7

4D

MS

13

A9

RS

64

7-

1.2

50

37

-5

.42

4*

**

21

-9

49

.63

26

,72

9.6

6-

0.9

97

*1

2.9

0.1

87

28

-0

.28

2*

**

0.6

33

7.1

46

2,7

63

-1

43

.61

1*

**

32

7

5D

MS

23

A9

N9

8-

5.5

28

**

*3

21

.13

22

38

18

.20

18

,28

1.7

7-

0.1

00

14

.65

.06

2*

**

42

0.0

18

0.8

91

9.3

13

2,5

10

13

.75

04

77

6D

MS

23

A9

Rio

0.6

67

43

-5

.09

0*

**

23

-8

73

.82

67

,75

6.3

30

.42

51

5.4

-3

.60

2*

**

29

-0

.15

7*

0.9

44

93

.03

5*

*3

,84

7-

77

.86

15

04

7D

MS

23

A9

RS

CN

50

08

-3

.13

9*

43

-0

.45

12

3-

92

6.4

65

6,8

53

.88

-0

.55

31

3.7

-0

.32

73

2-

0.0

76

0.7

8-

25

5.2

71

2,8

14

-4

1.3

61

41

6

8D

MS

23

A9

RS

64

78

.00

0*

**

54

4.4

10

**

*2

99

82

.09

08

,80

6.3

30

.22

81

3.7

-1

.13

3*

32

0.2

15

**

1.0

4-

25

7.0

76

2,4

26

10

5.4

72

*5

48

9D

MS

25

A9

N9

85

.69

4*

**

43

0.8

82

23

-1

94

.24

37

,81

2.5

5-

0.5

44

15

-6

.85

2*

**

35

0.0

04

1-

84

.10

42

,66

9-

2.3

89

52

5

10

DM

S2

5A

9R

io5

.11

1*

**

47

0.5

49

30

-2

92

.60

48

,88

0.7

70

.32

51

6.2

1.3

73

*3

8-

0.0

93

1.1

3-

51

1.8

26

**

3,1

05

-4

2.5

56

60

3

11

DM

S

25

A9

RS

CN

50

08

-5

.58

3*

**

41

-1

.25

72

35

19

.75

78

,84

3.3

30

.12

51

5.2

4.3

59

**

*4

10

.11

01

.08

54

7.8

68

**

3,8

79

55

.27

85

77

12

DM

S2

5A

9R

S6

47

-5

.22

2*

**

41

-0

.17

42

5-

32

.91

08

,33

4.5

50

.09

41

4.4

1.1

20

*3

8-

0.0

21

0.9

34

8.0

63

2,9

93

-1

0.3

33

49

7

13

DM

S2

8A

9N

98

-2

.72

2*

31

-1

.75

72

3-

86

1.1

04

7,8

89

.11

0.1

36

14

.82

.09

8*

**

41

-0

.05

40

.97

-3

39

.74

32

,77

7-

21

.80

65

26

14

DM

S2

8A

9R

io2

.13

94

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0.9

79

30

33

.86

89

,95

0.6

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28

14

.80

.77

83

5-

0.0

85

1.1

78

63

.20

1*

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4,8

43

-5

0.7

50

61

5

15

DM

S2

8A

9R

SC

N

50

08

2.1

11

45

1.5

49

28

82

6.7

85

9,8

93

.77

-0

.58

31

3.7

-2

.70

2*

**

32

0.0

51

1.0

6-

39

5.3

26

*3

,30

02

4.0

83

56

6

16

DM

S2

8A

9R

S6

47

-1

.52

84

11

.18

82

90

.45

19

,11

1.3

30

.67

51

4.2

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43

40

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71

.07

-1

28

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23

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14

8.4

72

57

5

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1.3

21

1.0

63

52

4.9

97

0.4

77

0.5

36

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78

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1.1

37

40

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5

*,

**

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Sig

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123


23A 9 RS 647 showed significant and positive SCA

effects apart from higher mean sugar contents. DMS

13A 9 Rio and DMS 23A 9 RS 647 were the only crosses

to exhibit significant and positive SCA effects for com-

puted bioethanol yields. However, the hybrids DMS

28A 9 Rio and DMS 25A 9 Rio were among the top

mean ethanol yielders though they have recorded insig-

nificant and negative SCA effects. For grain yield, DMS

28A 9 Rio, DMS 25A 9 RSCN 5008 and DMS

23A 9 Rio displayed significant SCA effects in positive

direction.

Heterosis

Mid-parental heterosis and better parental heterosis for

important traits like total biomass, juice yield, brix content

and computed ethanol yield were studied.

Mid-parental heterosis

The mid-parental heterosis for total biomass, juice yields

and computed ethanol yields are depicted in Fig. 1. For

total biomass and juice yields, 11 out of 16 hybrids

exhibited significant and positive heterosis. The hybrid

DMS 23A 9 RS 647 recorded 62 % heterosis for total

biomass while DMS 23A 9 N98 followed by DMS

13A 9 N 98 exhibited 79 and 69 % heterosis respectively

for juice yield. With respect to brix content, only one

hybrid DMS 28A 9 RS 647 has shown significant heter-

osis up to 9 % while five hybrids recorded significant

heterosis in negative direction. Stem sugar heterosis values

up to 7.39 % in Texas, USA were reported (Corn 2008).

Significant and positive heterosis for computed ethanol

yields ranged from 26 % in DMS 25A 9 RS 647–98 % in

DMS 23A 9 RS 647.

Better parent heterosis

Six hybrids have shown significant and positive better

parent heterosis ranging between 12 to 41 % for total

biomass. The hybrid DMS 23A 9 RS 647 which exhibited

significant mid parent heterosis for total biomass also

registered significant heterosis (41 %) in positive direction

(Table 6). For juice yield, seven out of 16 hybrids have

shown significant and positive better parent heterosis. The

hybrid DMS 28A 9 RSCN 5008 registered 60 % signifi-

cant heterosis. For brix content, 12 hybrids exhibited sig-

nificant heterosis in negative direction. Better parent

heterosis for stem brix up to 45 % was observed in hybrids

(Itai et al. 2009). Eight out of 16 hybrids have shown

significant and positive better parent heterosis for

computed bioethanol yields which ranged between 19 and

86 %. The hybrids viz., DMS 23A 9 RS 647 (86 %), DMS

28A 9 RS 647 (69 %), DMS 23A 9 N98 and DMS

28A 9 RSCN 5008 (62 %) have shown more than 60 %

better parent heterosis for this trait.

Fig. 1 Mid-parent heterosis for a total biomass, b. juice yield and

c computed ethanol yields in sweet sorghum hybrids


123


Discussion

The mean squares due to environment, entries and their

interactions were significant indicating the genotypic

diversity and their responses to environment. Partitioning

of the mean squares into variations attributable to testers

and line 9 testers showed that variation within each group

with environment was significant for most of the traits.

Similar to the present investigations, in a study on com-

bining ability and heterosis in sweet sorghum germplasm,

significant site 9 hybrid interaction effects for stem brix,

stem biomass weight ha-1 and stem brix-juice index were

reported (Itai et al. 2009). In a study on tropical sorghums

across four environments, significant mean squares due to

environment, entries and environment-entries interactions

were observed (Kenga et al. 2004). Testers were more

variable than lines in a line 9 tester study across locations

and years in forage sorghum (Mohammed and Mohamed

2009) and in sweet sorghum (Indhubala et al. 2010) similar

to the present study. The significance of line 9 tester effect

for most of the traits except brix content suggests the

presence of high heterotic responses for these traits. Mean

stem �brix and stem �brix-juice index were not significantly

(P B 0.05) different between the parents, hybrids and the

standard check variety in a study on combining ability and

heterosis of sorghum germplasm for stem sugar traits under

off-season conditions in tropical lowland environments

(Itai et al. 2009) which is similar to the present findings.

The estimates of variances due to combining ability

revealed the significance of both additive (fresh stalk yield,

juice yield, brix content) and the non-additive type of gene

actions (total biomass and grain yield) for important traits.

This implies that improvement for these traits can be

achieved through both selection and hybridization. More-

over a definitive separation of additive, dominance and

non-additive genetic effects for these traits requires eval-

uation of additional sets of genetic material. The total

biomass yields among the hybrids ranged from 26 to 54 t/

ha in the present investigation and this trait is of paramount

importance in breeding sweet sorghum for biofuel pro-

duction. Similar to the present study, stem biomass yields

of 47.9, 46.4 and 39.5 t ha-1 for cultivars Wray, Keller and

Rio, respectively were reported from in-season evaluations

in Indonesia (Tsuchihashi and Goto 2004). Heterosis

breeding could be exploited for increasing the biomass

yields owing to the importance of non-additive gene action

in determining this character. The other important biofuel

trait, i.e., brix content ranged from 12.9� to 16.2� in the

hybrids and was controlled by additive gene action and

further gains for this trait can be achieved through selec-

tion. Earlier studies (Tsuchihashi and Goto 2004; Woods

2000) have demonstrated stem sugar concentrations of

between 14.0 and 18.5� brix with specialized sweet sor-

ghum cultivars. Stem �brix values of about 13 under dry-

land production were reported in Indonesia (Tsuchihashi

and Goto 2004). The interaction effect of SCA variance

with that of environment was significant for most of the

characters studied. The predominant role of non-additive

gene action for plant height, stem girth, total soluble solids,

millable sweet-stalk yield and extractable juice yield was

Table 6 Better parent heterosis in 16 sweet sorghum hybrids

Hybrid Total biomass (tons/ha) Juice yields (l/ha) Brix (%) Computed ethanol yields (l/ha)

DMS 13A 9 N 98 -16.52** 42.14** -10.69** 54.62**

DMS 13A 9 Rio -34.81** -2.34 -18.02** 6.33

DMS 13A 9 RSCN 5008 16.52** 24.92** 1.95 28.25*

DMS 13A 9 RS 647 -4.06 2.72 -16.00** 0.72

DMS 23A 9 N 98 -16.18** 48.02** -16.54** 62.32**

DMS 23A 9 Rio 7.18 -21.24** -15.09** -31.38**

DMS 23A 9 RSCN 5008 12.43* 18.66 -10.93* 19.33*

DMS 23A 9 RS 647 41.33** 34.42** -0.48 86.43**

DMS 25A 9 N 98 15.09** -10.46 -14.12** -0.90

DMS 25A 9 Rio 17.68** -9.82 -10.87** -17.80*

DMS 25A 9 RSCN 5008 7.99 1.35 -9.09* 8.89

DMS 25A 9 RS 647 8.88 -4.48 -13.80** -6.33

DMS 28A 9 N 98 -21.61** 27.42* -15.14** 54.42**

DMS 28A 9 Rio 1.93 1.04 -18.63** -16.21*

DMS 28A 9 RSCN 5008 11.91* 59.80** -11.07* 62.23**

DMS 28A 9 RS 647 2.77 39.08** -2.38 68.94**

*, ** Significant at P B 0.05 and 0.01, respectively


123


observed in a study on heterosis and combining ability for

juice yield related characteristics in sweet sorghum

(Sankarapandian et al. 1994) indicating the importance of

heterosis breeding for improving these traits.

The identification of new hybrid parents with good

combining ability for different traits of interest was one of

the important objectives of the present study. For total

biomass, DMS 23A and DMS 25A among female parents

and RSCN 5008 and RS 647 among males are potential

parents for improving the total biomass as these parents

exhibited high and significant GCA values. These parents

can also be utilized for development of feedstock material

for the production of 2nd generation biofuels apart from

their use for production of hybrids to address biofuel from

sweet sorghum juice. For fresh stalk yield, DMS 28A from

female group and Rio among males were promising while

the former one was a good combiner for juice yield and

grain yield also and these can be used in hybrid making to

address ethanol production from juice without compro-

mising on grain yields. For brix content, DMS 25A among

female parents and Rio among males were potential parents

and thus can be exploited for improving the brix content. It

was gratifying to note that Rio had also exhibited signifi-

cant and positive GCA effects for total sugar content,

computed bioethanol and grain yields. It was observed that

for various characters, high combiners were the male

parents.

In this study, the hybrids DMS 13A 9 Rio (for total

biomass, fresh stalk yield, juice yield, juice extraction, total

sugar content and computed bioethanol yields), DMS

23A 9 RS 647 (for total biomass, fresh stalk yield, total

sugar content and computed bioethanol yields), DMS

13A 9 RSCN 5008 (for total biomass and brix content),

DMS 13A 9 N 98, DMS 23A 9 Rio, DMS 25A 9 RSCN

5008 and DMS 28A 9 Rio (for grain yield) exhibited

significantly higher SCA effects. It is evident that most of

the hybrids promising for various traits were observed to be

constituted from hybrids with both or one parent exhibiting

significant GCA effects and produced hybrids with higher

SCA effects. The significance of both GCA and SCA

effects suggesting both additive and non-additive gene

effects for grain yield was observed (Itai et al. 2009).

The heterosis levels observed in this study could also

explain the high biomass, juice and computed ethanol

yields observed for hybrids as compared to the parents.

Most of the hybrids which recorded significantly positive

heterosis also recorded higher SCA effects.

Parental selection for crop improvement programmes

cannot be based on SCA effects alone, but in association

with hybrid means and GCA effects of the parents involved

(Marilia et al. 2001). It is prudent to consider only those

hybrids between parents with positive and significant GCA

effects because genetic gain is realized in the presence of

sufficient additive variances. The interaction effect of SCA

variance with that of environment was significant for all the

characters except juice extraction. This implies that the

environment significantly influenced the expression of non-

additive gene effects. The observation of significant envi-

ronmental influences on SCA effects is consistent with

reports that genotype 9 environment interaction is impor-

tant in sorghum (Panse and Sakhatme 1964; Chapman et al.

2000; Yu and Tuinstra 2001). Therefore, it is necessary to

conduct multi-location testing for GCA and SCA to select

the best parents and potential hybrids (Itai et al. 2010)

before deploying specific sweet sorghum hybrids in dif-

ferent environments for commercial cultivation which

ultimately benefit the poor farmers of the semi-arid tropics.

Conclusions

The parents viz., DMS 28A among females for fresh stalk,

juice and grain yields, Rio among males for fresh stalk

yield were identified as promising for biomass traits as they

have shown positive and significant GCA and in combi-

nation large SCA effects. For quality traits, DMS 25A

among female parents and Rio among males were found to

be promising as potential parents for brix content while the

latter had also exhibited significant and positive GCA

effects for total sugar yield and computed bioethanol

yields. All these parents can be used in sweet sorghum

cultivar development programs to address ethanol pro-

duction from juice without compromising on grain yields

and offer solution to the ongoing food vs fuel debate. The

study also demonstrated the significance of both additive

and the non-additive type of gene actions for important

traits. Most of the hybrids which recorded significantly

positive heterosis also recorded higher SCA effects. Fur-

ther the study identified the hybrids DMS 13A 9 Rio and

DMS 23A 9 RS 647 with significantly higher SCA effects

for sweet sorghum productivity traits. These hybrids would

be recommended for further testing across many locations

in the semi-arid target production environments for ethanol

production.

Acknowledgments Authors are grateful to the Indian Council of

Agricultural Research for financial support and the staff at Rahuri and

Coimbatore locations for their assistance in running the sweet sor-

ghum trials.

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