Abstract

Media summary

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 y_j represents the value of plant height, or degree of curvature of the panicle, μ_i represents the mean of the trait values and p_i 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 (χ²_0.05=5.15); for
H₂, χ²= (-553.49+557.40)=7.82, so the hypothesis of only one major gene should be rejected (χ²_0.05=5.99,χ²_0.01=9.21); for H₃,χ²= 2(-557.40+575.76)=36.72, so the hypothesis that the major gene had an additive effect should be rejected (χ²_0.01 =6.63); for H₄,χ²=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 (χ²_0.05 =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 H_1, 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 (χ²_0.01 =8.36); for H₂, χ²=2(-747.17+747.61)=0.88, so the hypothesis that a major gene was present should be accepted (χ²_0.05 =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 (χ²_0.05=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 (χ²_0.01=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.