Maize Genetics Cooperation Newsletter 80. 2006.

 

New Delhi, India

Indian Agricultural Research Institute

 

Heritability and correlation studies in sweet corn for quality traits, field emergence and grain yield

--Kumari, J; Gadag, RN; Jha, GK

 

       Ten sweet corn and seven field corn genotypes were studied for estimating components of genetic variance and combining ability for ear-related and biochemical traits using diallel and �line-X-tester� mating designs.  The study was carried out at the Division of Genetics and Division of Environmental Science, Indian Agricultural Research Institute, during 2003-2004.  Diallel crosses were made among six inbred lines, including three each of sugary and shrunken genotypes, while in later crosses seven field corn inbreds were crossed as female lines with four sweet corn inbreds as tester parents.  The details regarding pedigree, source of origin and endosperm mutants are given in Table 1.

       Analyses of variance by diallel shows the mean sum of squares is highly significant for all nine traits except reducing sugar (Table 2).  In the line-X-tester analysis (Table 3), parents as a whole are significant at 1% for all characters, while the partitioned source of variance for female parents indicated significance for starch, carbohydrate, grain weight, field emergence and TSS.  This meant that field corn lines have significant variability for these traits while significant for sugar components and phytoglycogen.  As far as male parents or sugary lines are concerned, these were significant for all sugar components, phytoglycogen and total carbohydrate components.  As it is well known that field and sweet corn populations are genotypically and phenotypically different, the female vs. male source of variation is significant for all traits.  Simi-
Table 1.  Pedigree and source of origin of inbred lines.

 

Inbreds

(Code #)

Pedigree

Source population

Endosperm mutation

DMB321

IPA40-f-17-1-1-4-1-1-1-f

AD-609

Normal

DMB322

TCA-22-3-1-1-2-f-#-f-1-1

A-64

Normal

DMB323

IPA-1-f-16-2-#-f-1

A-64

Normal

DMB324

IPA-34-5-f-1-1

MDR-1

Normal

DMB325

PC2HS-31-f

PC2composite

Normal

DMB326

IPA-3-6-10-3-1-1-1-2-1

A-64

Normal

DMB327

TCA-21-1-b-1-1-1-3-1

AD-609

Normal

SCI301

SCMD90 (01R)-2-1-3-1

Madhuri

su

SCI302

SCMD90 (01R)-3-1-2-1

Madhuri

su

SCI303

SCMD90 (01R)- 4-2-1-2

Madhuri

su

SCI304

SCMD90 (01R)- 4-3-2-1

Madhuri

su

SCI305

SCMD90 (01R)-5-4-1-1

Madhuri

su

SCI306

SCPRHY85 (01R)-2-1-2-3

SOOK SH137

sh

SCI307

SCPRHY85 (01R)-6-3-1-2

SOOK SH137

sh

SCI308

SCPRHY85 (01R)-7-3-2-1

SOOK SH137

sh

SCI309

SCPRHY90 (01R)-2-2-1-2

SOOK SH138

sh

SCI310

SCPRHY90 (01R)-3-1-3-1

SOOK SH138

sh

 

larly, hybrid and parent vs. hybrid mean sum of squares are significant for most of the traits.  This suggests the utilization of non-sweet germplasm in the improvement of sugary genotypes through hybridization and introgression, followed by backcrossing for characters such as field emergence, plant stand and yield.

       The correlation coefficients were calculated to determine the degree of association of characters among the kernel quality components total soluble solids (TSS), grain yield and field emergence.  Phenotypic correlations were computed using the formula given below.  Pearson product-moment correlation coefficients were calculated using inbred line means from replicated trials of diallel and line-X-tester analysis using the SPSS 10.0 package.

     

Where,   

rp

= Phenotypic correlation       

Cov (XY) p

= Phenotypic covariance between the characters X and Y

X2p and Y2p

= Phenotypic variance of the characters X and Y, respectively

Phenotypic correlation coefficients were compared against �r� values at (n-2) d.f. at the probability levels of 0.05 and 0.01 to test their significance.  The results of correlation analysis for the traits studied in this experiment  are presented in Table 4.

       The main objective associated with this study was to understand the relationship between field emergence, grain weight and kernel quality traits, including total soluble solids (TSS).  The correlation analysis revealed that total sugar is positively correlated with reducing sugar and non-reducing sugar with a high level of significance (p< 0.001).  Phytoglycogen and total soluble solids had significant correlation with total sugar, with p values equal to 0.011 and 0.007, respectively.  However it had negative significant correlation with starch, carbohydrate, grain weight and field emergence.  The same trend was exhibited by reducing sugar as well as non-reducing sugar.  Starch concentration in dry mature kernels was most highly correlated with total carbohydrate (r = 0.78), followed by field emergence (r = 0.69) and grain weight (r = 0.52) while it was negatively correlated with all other characters.  The phytoglycogen content had a highly negative correlation coefficient with


 

Table 2.  Analysis of variance for diallel.

 

Source

d.f.

Mean sum of squares

Total sugar (%)

Reducing sugar (%)

Non-reducing sugar (%)

Total Starch (%)

Phytoglycogen (%)

Total carbohydrate (%)

Grain weight

Field emergence

Total soluble solids (TSS)

Replication

2

0.48

0.087

0.54

22.01

0.47

29.09

30.96

44.92

0.29

Treatment

20

14.04**

0.34

11.22**

209.24**

89.87**

89.38**

9.68**

236.54**

3.13**

Error

40

1.68

1.58

1.65

22.06

0.50

26.07

3.78

14.17

1.11

* and ** indicate significance level at 1% and 5 % respectively.

 

Table 3.  ANOVA for parents and hybrids (biochemical traits) in line-X-tester.

 

Source

d.f.

Mean sum of squares

Total sugar (%)

Reducing sugar (%)

Non-reducing sugar (%)

Total Starch (%)

Phytoglycogen (%)

Total carbohydrate (%)

Grain weight

Field emergence (%)

Total soluble solids (TSS)

Replication

2

2.25

0.77

5.09

136.81

0.04

103.79

5.03

37.27

0.29

Parents

10

51.37**

2.18**

33.86**

516.53**

117.66**

132.07**

50.13 **

335.60**

3.13**

Females

6

0.61

0.16

0.29

120.24**

0.032

117.83**

29.20 **

407.19**

3.07**

Males

3

27.13**

0.35*

24.17**

10.54

165.21*

76.13*

16.33

141.60

1.14

Females vs. Males

1

428.67**

19.76**

264.35**

4412.31**

680.83**

385.35**

277.09 **

488.08**

9.44**

Hybrids

27

12.23**

0.97**

13.80**

240.10**

7.78**

198.37**

28.77 **

173.89**

0.76

Parents vs. hybrids

1

773.98**

37.18**

471.93**

378.42**

83.81**

0.64

5.37

8713.50**

117.87**

Error

76

2.10

0.09

2.15

31.60

0.37

27.57

6.53

79.61

1.11

* and ** indicate significance level at 1% and 5%, respectively.

 

Table 4.  Correlation coefficients among kernel characteristics, yield and field emergence.

 

 

TS

RS

NRS

ST

PH

TC

GW

FE

TSS

Total sugar (TS)

1.00

0.89

0.99**

-0.81**

0.43*

-0.54**

-0.49*

-0.28

0.46*

Reducing sugar (RS)

 

1.00

0.84**

-0.82**

0.61**

-0.47*

-0.64**

-0.34

0.50*

Non-reducing sugar (NRS)

 

 

1.00

-0.78**

0.37

-0.54**

-0.44*

-0.25

0.43*

Total starch (ST)

 

 

 

1.00

-0.67**

0.78**

0.51**

0.69**

-0.30

Phytoglycogen (PH)

 

 

 

 

1.00

-0.13

-0.67**

-0.28

0.19

Total Carbohydrate (TC)

 

 

 

 

 

1.00

0.94**

-0.05

-0.13

Grain Weight (GW)

 

 

 

 

 

 

1.00

0.54**

-0.35

Field Emergence (FE)

 

 

 

 

 

 

 

1.00

0.23

Total soluble solids (TSS)

 

 

 

 

 

 

 

 

1.00

* and ** indicate significance at 1% and 5%, respectively.

 

 

grain weight and starch content, whereas there was no significant correlation with field emergence and total soluble solids.  Further, total carbohydrate exhibited negative but significant correlation with all sugar components and positive significant correlation with starch content.  As far as grain weight is considered, there was significant correlation in a negative direction with all quality traits except starch and carbohydrate content.  It also displayed a positive correlation with field emergence, but negative with TSS.  Field emergence, the important aspect for sweet corn, was positively correlated with only two traits viz. starch content and grain weight.  When the total soluble solids were studied at 20-22 days after pollination to observe the relationship between the above-mentioned characters, highly significant correlation was observed with sugar components.

       The sugar components, in general, were highly correlated among themselves and negatively correlated with starch content, total carbohydrate, grain weight and field emergence.  This kind of association was also observed by Churchill and Andrew (Crop Sci. 24:76-81, 1984) and Azanza et al. (Euphytica 87:7-18, 1996).  The lower correlation of field emergence with high sugar level can be attributed to the fact that high sucrose concentration in the endosperm during kernel development interferes with the normal development of either the endosperm or the embryo, resulting in a decrease in the ability of the kernel to germinate and emerge in the field.  Douglass et al. (Seed Sci. Tech. 21:433-445, 1993) also reported such a negative association of field emergence with sugar concentration and suggested that genotypes with greater sugar concentrations would display a more negative osmotic potential during seed hydration and during germination, and that the steep osmotic gradient can induce the rapid influx of water leading to membrane disruption and the leakage of the water-soluble fraction from the endosperm.  Starch concentration in dry matured kernels is highly correlated with field emergence (r = 0.69, p< 0.01) and suggests that the carbohydrate reserve accumulated during kernel maturation plays an important role in field emergence.  These reserves remain available to the embryo to be metabolized and used as an energy source for germination (Douglass et al., 1993).  Total starch concentration was found to be highly correlated with kernel dry weight.  This is expected since starch is the major contributor to the grain weight.  As a consequence, grain weight is also positively correlated with field emergence (r = 0.54, p<0.01).

The unfavorable correlation coefficients between sugar content and grain weight suggested that in breeding programmes it is difficult to obtain high yielding sweet maize hybrids.  A similar result was obtained by Has (MNL 77:74-75, 2003), and it is also clear from the present study of hybrid performances for these two traits.  Furthermore, the positive association between total soluble solids and sugar components implied that estimation of TSS at 20 days after pollination could help in the evaluation and screening of a large number of genotypes for assessing sugar content.  However the nonsweet germplasm has the potential to improve sugary genotypes for traits like field emergence, plant stand and yield.

 

 

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