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Genetic analysis of plant height and panicle erectness of rice

Wang Bolun, Wang Shu, Huang Yuancai

Shenyang Agricultural University, Shenyang, 110161, China. Email: blwang@online.ln.cn

Abstract

Analysis of plant height and panicle type was conducted in two populations, Norin 315/Shennong 8801 and Norin 310/Shennong 8801, using the Maximum Likelihood Method for qualitative-quantitative traits. Results indicated that plant height of Shennong 8801 was mainly controlled by a single, dominant gene and the gene could be modified by a group of polygenes. The panicle type Shennong 8801was mainly determined by an additive gene and the gene could be modified by a group of polygenes too. The polygenes in Norin 315 might be different from that in Norin 310. There was a positive correlation between the plant height and the panicle curve degree.

Media summary

Plant height, or panicle type, of Shennong 8801 is determined by a major gene and polygenes

Key words

rice, plant height, panicle erectness

Introduction

In rice plants, reduced height (dwarfness) is one of the most important breeding objectives, because this characteristic is closely related to plant type, fertilizer response and lodging resistance (IRRI, 1985). Panicle type may be another important trait for increasing yield potential of rice plants (Wang et al., 1997). Further understanding of the inheritance of these traits is required.

Methods

Norin 315 and Norin 310, two varieties with curved panicles, were crossed with erect panicle variety Shennong 8801 in Shenyang Agricultural University, China. The F1 generations were planted and the same crosses were repeated. The F2 and F1 generations, and their parents, were planted in the same field. Plant height of the cultivars and degree of curvature of the main panicle were investigated. The frequency distributions of plant height and degree of panicle curvature were analyzed by the Maximum Likelihood Method for qualitative-quantitative traits (Mo, 1993; Jiang et al., 1995). If yj represents the value of plant height, or degree of curvature of the panicle, μi represents the mean of the trait values and pi the probability of a mixture type for traits in the F2 generation. The analysis method is listed as follows.

Distribution of a single normal-

(1)

in which

,

(2)

Distribution of multi-individual normal.

(3)

in which

(4)

Distribution of mixed normal-

(5)

in which

(6)

According to this, EM method was performed on computer.

Expectation step

(7)

Maximization

,

(8)

(9)

(10)

Results

Plant height

The results showed that plant height segregated significantly. Some individuals exceeded their parents in height in the F2 generations (Table 1). The probability distribution of plant height appeared in multiple peaks. The plant height of the cross belongs to a qualitative-quantitative trait. The results of analysis of the plant height of Norin 315/Shennong 8801 are presented in Table 2. For
H1, χ2= 2(-557.40+568.28)=21.76, so the hypothesis should be rejected (χ20.05=5.15); for
H2, χ2= (-553.49+557.40)=7.82, so the hypothesis of only one major gene should be rejected (χ20.05=5.99,χ20.01=9.21); for H32= 2(-557.40+575.76)=36.72, so the hypothesis that the major gene had an additive effect should be rejected (χ20.01 =6.63); for H42=2(-557.40+557.84) =0.88, so the hypothesis that the major gene was completely dominant should be accepted; for H5, χ2=2(-549.23+557.40)=16.34, so the hypothesis that the F2 generation was a mixed population with three equal variances (six peaks) should be accepted and only one major gene should be rejected (χ20.05 =12.59). It means that genetic difference in plant height in this cross is related to one major dominant gene and a group of polygenes which can modify the dominant gene.

Table 1. Plant height for F2 generations and parents

Parent or cross

Minimum

Maximum

Mean

SD

Norin 315

96.3

108.6

101.9

2.50

Shennong 8801

87.3

97.5

93.7

2.41

Norin 315/Shennong 8801

75.6

121.7

99.8

9.24

Norin 310

91.8

103.3

97.6

3.03

Norin 310/Shennong 8801

70.5

129.0

98.6

10.27

Table 2 Maximum likelihood estimates of parameters of plant height of Norin 315/Shennong 8801 in the F2

No. of EM

Parameter estimates

σ 2 lnL

iteration p1 p2 p3 p4 p5 p6 p7

μ 1 μ 2 μ 3 μ 4 μ 5 μ 6 μ 7

 

H1: Model without major gene

 
   

99.8

85.4 -568.28

 

H2: One-locus model of major gene

 

109

0.25 0.50 0.25

92.0 97.5 113.1

26.4 -557.40

 

H3: Additive model

 

128

0.25 0.50 0.25

92.4 102.9 113.4

37.0 -575.76

 

H4: Complete dominance model

 

19

0.75 0.25

95.6 112.7

32.3 -557.84

 

H5: Mixture model with three and more normals (?)

 

98

0.02 0.74 0.24

77.2 96.0 113.0

25.3 -553.49

210

0.02 0.44 0.34 0.20

76.6 93.3 100.4 114.2

16.2 -552.23

304

0.02 0.44 0.34 0.17 0.03

76.6 93.3 100.4 114.2 114.2

16.2 -552.23

468

0.02 0.26 0.42 0.13 0.06 0.11

76.4 90.7 97.8 105.8 112.7 116.6

7.4 -549.23

778

0.02 0.26 0.42 0.13 0.06 0.09 0.02

76.4 90.7 97.8 105.8 112.7 116.6 116.6

7.4 -549.23

Panicle type

The result obtained from the experiments showed that the panicle of Norin 315 and Norin 310 belonged to the curved type, while that of Shennong 8801 belonged to the erect type. The panicle types of F2 generation of two crosses showed significant segregation (Table 3). The result of analysis on the panicle type of the plants in F2 generation of cross Norin 315/Shennong 8801 is presented in Table 4. For H1, χ2=2(-747.61+759.73)=24.24, the value of the χ2 was very significant and so the hypothesis that a major gene was nonexistent should be rejected (χ20.01 =8.36); for H2, χ2=2(-747.17+747.61)=0.88, so the hypothesis that a major gene was present should be accepted (χ20.05 =5.99), for H3, χ2=2(-747.61+748.77)=2.32, so the hypothesis that the major gene was an additive gene should be accepted (χ20.05=3.84); for H4, χ2=2(-747.61+758.21)=21.20, the hypothesis that the major gene was a completely dominant should be rejected (χ20.01=3.32); for H5, χ2=2(-739.25+747.61)=8.36, this meant that there might be polygenes, besides the major additive gene.

Table 3 Results of panicle type investigation in F2 generations and parents

Parent or cross

Minimum

Maximum

Mean

SD

Norin 310

89.2

112.0

98.4

7.06

Shennong 8801

2.0

14.3

7.1

3.13

Norin 310/Shennong 8801

1.6

117.6

55.2

29.80

Norin 315

95.6

128.3

115.0

8.75

Norin 315/Shennong 8801

4.6

123.0

62.8

31.54

Table 4 Maximum likelihood estimates of parameters of panicle type of Norin 315/Shennong 8801 in the F2

No. of EM

Parameter estimates

σ2 lnL

Iteration p1 p2 p3 p4 p5 p6 p7

μ1 μ 2 μ 3 μ 4 μ 5 μ 6 μ 7

 

H1: Model without major gene

 
   

62.8

994.5 - 759.73

 

H2: One-locus model of major gene

 

44

0.25 0.50 0.25

24.3 62.0 104.0

154.4 - 747.61

 

H3: Additive model

 

38

0.25 0.50 0.25

25.6 65.3 105.0

156.0 - 748.77

 

H4: Complete dominance model

 

80

0.75 0.25

49.0 97.4

157.2 - 758.21

 

H5: Mixture model with three and more normals

 

71

0.29 0.45 0.26

25.3 62.7 103.9

152.3 - 747.17

293

0.11 0.18 0.45 0.26

25.3 25.3 62.7 103.9

152.3 - 747.17

206

0.08 0.21 0.45 0.17 0.09

25.3 25.3 62.7 103.9 103.9

152.3 - 747.17

423

0.05 0.14 0.19 0.29 0.14 0.19

17.8 17.8 42.1 63.4 84.4 109.2

56.2 - 742.37

268

0.05 0.13 0.18 0.25 0.14 0.15 0.10

17.4 17.4 41.1 61.1 77.7 99.5 115.5

37.4 - 739.25

The Table 5 presents the result of the progeny test for the cross Norin 315/Shennong 8801. The results showed that the plants could be divided into three groups according to the plant height. The frequency of semi-dwarf : semi-dwarf+tall : tall was about 0.25 : 0.5 : 0.25. In the semi-dwarf+tall group, the frequency of the semi-dwarf : tall was about 0.75 : 0.25. This suggested that plant height was mainly determined by a dominant gene. The segregation of the plant height in semi-dwarf group, or in tall group, was not significant. It meant that the segregation of the plant height was determined by the polygenes. The frequency of erect panicle : semi-erect panicle : curved panicle was about 0.25 : 0.5 : 0.25. In each group, the segregation of panicle type was not significant.

The result of the progeny test in Norin 310/Shennong 8801 was similar to those in Norin 315/Shennong 8801. In F2 and F3 generations of the two crosses, there was a significant positive correlation between the plant height and the degree of panicle curvature. Most of the plants with erect panicles were semi-dwarf. while all of the tall plants had curved panicles.

Table 5 The progeny tests in the cross Norin 315/Shennong 8801

Panicle types

Degree of panicle curvature ()

Plant height (cm)

 

Minimum

Maximum

Mean

SD

Minimum

Maximum

Mean

SD

Erect and

1

5

3.2

1.0

84.8

93.2

89.5

4.2

semi-erect

3

30

13.7

8.0

83.0

102.2

94.5

4.9

 

3

35

12.6

9.2

82.5

99.5

91.4

4.0

 

4

55

15.8

11.5

88.0

100.0

95.0

3.4

 

11

66

42.2

16.9

90.2

108.3

97.4

4.3

 

3

63

31.5

21.5

87.0

116.6

100.4

8.8

 

5

72

65.1

37.7

95.2

125.1

107.6

10.6

 

5

70

40.1

22.8

89.5

120.0

102.1

9.8

 

13

90

40.3

25.8

93.5

114.8

103.2

7.5

 

5

40

19.5

13.7

89.0

120.5

105.5

9.2

 

11

68

44.9

18.3

82.0

115.5

100.0

8.5

 

3

65

39.3

23.5

89.0

122.0

107.1

11.8

 

3

75

38.9

20.5

92.0

117.5

100.5

8.3

Curved

30

70

53.9

11.5

106.8

116.3

110.7

3.0

 

50

90

64.1

9.6

101.0

114.0

107.9

3.8

 

60

140

84.5

21.9

103.0

118.5

110.6

4.3

Conclusion

The results of genetic analysis indicated that the plant height of Shennong 8801 was controlled by a major dominant gene and by a group of modifying polygenes. The major semi-dwarf gene might be different from sd-1. The panicle type of Shennong 8801 was determined by a major additive gene and by a group of modifying polygenes. The polygenes in Norin 315 might be different from that in Norin 310.

In general, there was a positive correlation between the plant height and curvature of the panicle. This suggests that the semi-dwarf gene might be linked with the gene for erect-panicle, or there may be pleiotropic effects. This needs to be studied further.

Acknowledgements

The National 863 project (2001AA241015) and the Liaoning Science Foundation project (99101002) of China

References

Donald C M. (1968). The breeding for crop ideotypes. Euphytica. 17, 385-403.

International Rice Research Institute (1985). Rice Genetics. IRRI. 260-336.

Jiang C J et al (1995). Genetic analysis for qualitative-quantitative traits, IV. Application of the Maximum likelihood method. Acta Agronomica Sinica. 21(6), 641-648.

Mo H D (1993). Genetic analysis for qualitative-quantitative traits, II. Generation means and genetic variances. Acta Agronomica Sinica. 19(3), 193-200.

Wang B L et al (1997). Studies on genetic activities of semidwarfism and erect-panicle in rice. Journal of Shenyang Agricultural University. 28(2), 83-87.

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