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The major gene and polygene effects of ornamental traits in bearded iris (Iris germanica) using joint segregation analysis
Scientia Horticulturae 260 (2020) 108882
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The major gene and polygene effects of ornamental traits in bearded iris (Iris germanica) using joint segregation analysis
T
Zhuping Fan, Yike Gao⁎, Rong Liu, Xinzi Wang, Yanchao Guo, Qixiang Zhang Beijing Key Laboratory of Ornamental Plants Germplasm Innovation & Molecular Breeding, National Engineering Research Center for Floriculture, School of Landscape Architecture, Beijing Forestry University, No. 35 Qinghua East Road, Haidian District, Beijing, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Bearded iris Heritability Ornamental traits Joint segregation analysis Major gene Polygene
Bearded iris (Iris germanica) is an indispensable horticultural perennial in the garden of spring. Therefore, improving their ornamental value is of great importance in the process of breeding. In order to find out whether the inheritance of some ornamental characters in bearded iris was controlled by major genes or polygenes, the joint segregation analysis was applied to investigate the inheritance of the six characters related to ornamental values in six generations (P1, P2, F1, F2, BC1P1 and BC1P2), including plant height (PH), leaf length (LL), height of individual flower (HF), diameter of flower (DF), length of fall (LF) and width of fall (WF). The six tested characters performed large range of coefficient of variation in the offspring generations, from 8.11% to 16.48%, indicating the diversity of offspring’s phenotypic performances. The broad-sense heritability ranged from 4.55% (DF) to 51.19% (LF), suggesting the different ability to pass down these characters to the next generation. From the analysis follows the corollary that PH, HF and DF were all in accordance with the additive-dominanceepistasis major gene plus additive-dominance polygene genetic model (E-1). The optimum model for LL was the additive major gene plus additive-dominance polygene genetic model (E-3), while an additive-dominance major gene plus additive-dominance-epistasis polygene genetic model (D-0) was suitable for WF. Unlike the other five characters, LF accorded with the B-1 model, which was controlled by two major genes without polygene effect. It proved that the selection of LL and WF was more effective in early generations, while the selection of PH and DF would be more useful in late generations. This research shed some light on the inheritance pattern of ornamental characters in bearded iris, and laid solid foundation for further molecular breeding of ornamental plants.
1. Introduction Bearded iris (Iris germanica) refers to the large hybrid population in the Iris genus, which is characterized by thick, bushy ‘beard’ on three falls (lower petals). Their attractive appearance, ease of cultivation and propagation make them extraordinary prevalent and of great commercial value (Harkess et al., 2010; Li et al., 2016; Zhao et al., 2016). Bearded irises are among the most popular and indispensable landscape plants in the spring garden. Therefore, improving their aesthetic values has always drawn many iris breeders’ attention (Azimi et al., 2018; Bo et al., 2017). The ornamental characters, such as plant height (PH), leaf length (LL), height of individual flower (HF), diameter of flower (DF), length of fall (LF) and width of fall (WF), are closely related to their aesthetic values. However, due to the lack of hybrid populations and effective analysis method, it remains ambiguous whether the ornamental characters are controlled by major gene or polygene effects. As a result, the new cultivars with high ornamental values are primarily
⁎
produced after a large amount of labour-wasting and time-consuming hybridization practice without explicit purpose (Austin, 2005). Therefore, systematic and scientific researches are essential to decipher the in-depth inheritance patterns of ornamental characters in bearded iris (Guo, 2000). Numerous studies have focused on the inheritance of floral characters in iris, most of which paid attention to heritability. It was found in Iris hybrids that standard width, standard height and flower size showed high broad-sense heritability values (97%), indicating that these characters could be considered as useful traits in Iris hybrids selection (Azimi et al., 2018). Similarly, in our previous study (Fan et al., 2017), fourteen F1 generations were generated and the largest heritability (91.47%) was observed in the character of WF (width of fall). Besides the heritability analysis, our previous research about offspring of bearded iris cultivar ‘Halston’ and ‘White and Yellow’ showed that the fall would become slimmer in late generations such as BC1P2 (Fan et al., 2018). It is worth mentioning that the ectopic expression of
Corresponding author. E-mail address: [email protected] (Y. Gao).
https://doi.org/10.1016/j.scienta.2019.108882 Received 31 May 2019; Received in revised form 22 September 2019; Accepted 24 September 2019 0304-4238/ © 2019 Elsevier B.V. All rights reserved.
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phytoene synthase gene (crtB) in I. germanica pink cultivar ‘Fire Bride’ could cause several flower parts to develop different degrees of novel orange and pink colors, but failed to generate red flowers (Jeknic et al., 2014). The foregoing researches were trying to reveal the inheritance essence of ornamental traits in iris, but they only unveiled a few profiles owing to the complexity of inheritance patterns. In this research, we explored whether the ornamental characters were controlled by major genes or polygenes, which could provide more information about their inheritance patterns. To the best of our knowledge, this is the first report on the inheritance patterns for ornamental characters in bearded iris. Joint segregation analysis (JSA) is a statistical method to identify the complex genetic model of quantitative characters even without molecular data (Wang and Gai, 2001). Using this method, the major genes and polygenes which controlled the target characters could be detected in multiple populations. Apart from quantitative trait locus (QTL) mapping and genome-wide association study (GWAS), JSA was an alternative method to identify a quantitative trait locus with large genetic effects without the aid of marker information. This method has been widely acknowledged in the research of vegetables, including soybean (Wang and Gai, 2001), chickpea (Anbessa et al., 2006), wheat (Khan et al., 2012), melon (Qi et al., 2015) and Brassica (Cao et al., 2016; Zhang et al., 2010). Recently, the JSA method has been gradually applied in ornamental plants such as crape myrtle (Ye et al., 2017) and chrysanthemum (Song et al., 2018). However, the JSA method has not been employed in the genetic analysis of bearded iris. In this research, the major gene and polygene effects of six ornamental characters were investigated using joint segregation analysis. The objectives of this study were to better understand the genetic mechanisms which controlled the six ornamental characters in bearded iris, and to lay the groundwork for the future development of molecular markers related to ornamental characters. The results may shed some light on breeding more bearded irises with high aesthetic values.
2.2. Field experiment To avoid contamination from other pollens, artificial emasculation was carried out the day before full bloom, and the flowers were covered with bags after artificial pollination. In 2013, the F1 generation (220 individuals) were obtained. In the blooming season of 2015, the F1 generation were used to produce F2 generation (216 individuals) by strictly self-pollination and were backcrossed with two parents to generate BC1P1 generation (212 individuals) and BC1P2 generation (236 individuals). In each generation’s first blooming year, sixty individuals were randomly selected, and six ornamental characters were measured, including plant height (PH), leaf length (LL), height of individual flower (HF), diameter of flower (DF), length of fall (LF) and width of fall (WF).
2.3. Statistical analysis The six ornamental characters were measured in the F1, F2, BC1P1, BC1P2, female parent (P1) and male parent (P2) populations. The descriptive statistical analysis and frequency distribution histogram were generated through SPSS Statistics 18.0 program. The broad-sense heritability was estimated as the ratio of genotypic variance to the phenotypic variance, just as described by Kelly and Bliss (1975), in which HB represents the broad-sense heritability, and V represents the variance of each generation:
HB (%) =
VF2 − (VP1 + VP2 + VF1) ∕3 × 100%. VF2
2.4. Joint segregation analysis The joint segregation analysis was performed on the basis of phenotypic data from the six generations (P1, P2, F1, F2, BC1P1 and BC1P2) according to the method of Gai and Wang (1998). The phenotypic values were analyzed under the twenty-four genetic models, including one major gene (A), two major genes (B), polygene (C), one major gene plus polygene (D) and two major genes plus polygene (E). According to Akaike’s Information Criterion (AIC) (Akaike, 1977), the models with smaller AIC values were considered as the candidates for the best-fit model. Then a series of statistical tests, including Uniformity test (U21, U22 and U23), Smirnov test (nW2) and Kolmogorov test (Dn), were carried out on the candidate models, in order to check the accuracy (Wang and Gai, 1997). Finally, the first and second order genetic parameters were calculated from the evaluation of component distributions in the optimal genetic model. The SEA software (Cao et al., 2013) was used to analyze the segregation genetic parameters of the six generations in this research.
2. Materials and methods 2.1. Plant materials The bearded iris cultivar Iris ‘White and Yellow’ was selected as the female parent, while I. ‘Halston’ was chosen to be the pollen donator (Fig. 1). The two cultivars were inbred for five generations to guarantee the homozygosity of the populations. All the plants were cultivated in a breeding nursery (40°09′N, 116°27′E) in Beijing, China. The experimental materials were given the same soil, moisture, temperature and light condition.
Fig. 1. The performances of P1 (I. ‘White and Yellow’) and P2 (I. ‘Halston’). Bar 2 cm. 2
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Table 1 Descriptive statistics of the six ornamental characters in two parents and four progeny generations. Trait
Generation
Min
Max
Mean ± SD
Variance
Skewness
Kurtosis
CV(%)
PH/cm
P1 P2 F1 F2 BC1 P1 BC1 P2
35.6 30.5 41.0 24.6 34.5 34.2
59.1 41.1 58.5 51.9 66.1 55.9
50.32 36.08 49.18 41.60 47.40 47.42
± ± ± ± ± ±
7.30 3.94 5.71 6.00 7.81 5.30
53.32 15.49 32.65 35.97 60.94 28.08
−0.86 −0.31 0.01 －0.78 0.49 −1.08
0.92 0.44 −1.23 1.39 −0.30 1.00
14.51 10.92 11.61 14.42 16.48 11.18
LL/cm
P1 P2 F1 F2 BC1 P1 BC1 P2
42.6 33.6 42.5 26.9 36.6 35.4
57.4 39.8 59.0 52.5 66.4 57.2
49.74 37.74 50.96 41.10 48.27 48.13
± ± ± ± ± ±
5.41 2.78 5.70 6.21 7.92 4.74
29.32 7.75 32.47 38.51 62.75 22.48
0.26 −1.04 −0.02 −0.75 0.37 −0.74
−1.11 −0.86 −1.17 0.48 −0.53 0.93
10.88 7.37 11.19 15.11 16.41 9.85
HF/cm
P1 P2 F1 F2 BC1 P1 BC1 P2
9.5 9.1 9.1 6.2 7.0 6.4
11.9 12.3 12.3 11.8 11.9 12.6
10.76 ± 0.70 10.45 ± 1.36 10.57 ± 1.08 9.55 ± 1.24 9.94 ± 1.20 9.50 ± 1.48
0.49 1.85 1.16 1.53 1.45 2.19
−0.06 0.98 0.16 −0.42 −0.61 −0.45
0.55 1.23 −0.80 1.13 0.07 0.21
6.51 13.01 10.22 12.98 12.07 15.58
DF/cm
P1 P2 F1 F2 BC1 P1 BC1 P2
7.8 7.6 8.4 8.6 9.5 9.6
10.9 11.5 13.2 13.8 14.5 14.3
9.49 ± 1.05 10.32 ± 1.63 11.25 ± 1.38 11.24 ± 1.41 11.67 ± 1.17 11.71 ± 0.95
1.11 2.64 1.91 1.98 1.37 0.90
−0.22 −1.62 −0.76 −0.16 0.22 0.07
−1.12 2.52 −0.09 −0.80 0.36 2.05
11.06 15.79 12.27 12.54 10.03 8.11
LF/cm
P1 P2 F1 F2 BC1 P1 BC1 P2
6.5 6.0 5.6 4.8 6.5 6.0
8.8 6.9 8.5 8.9 9.5 9.9
7.70 6.54 7.23 7.51 8.09 7.44
± ± ± ± ± ±
0.62 0.35 0.85 0.92 0.80 0.89
0.39 0.12 0.73 0.84 0.64 0.80
−0.28 −0.90 −0.30 −0.93 −0.05 0.97
1.81 0.79 －0.73 1.78 −1.60 0.99
8.05 5.35 11.76 12.25 9.89 11.96
WF/cm
P1 P2 F1 F2 BC1 P1 BC1 P2
4.5 5.2 4.2 3.7 4.2 3.9
5.8 6.0 5.5 6.0 6.3 6.4
5.08 5.74 4.81 5.02 5.19 5.46
± ± ± ± ± ±
0.45 0.33 0.52 0.54 0.60 0.62
0.20 0.11 0.27 0.29 0.36 0.38
0.54 −1.43 0.31 −0.24 0.01 −0.49
−0.67 2.09 −1.55 0.31 −1.04 0.12
8.86 5.75 10.81 10.76 11.56 11.36
Note: PH plant height, LL leaf length, HF height of individual flower, DF diameter of flower, LF length of fall, WF width of fall.
3. Results
Table 2 Broad-sense heritability of six measured ornamental characters.
3.1. Descriptive statistics of the phenotypic data The F1 generation had the largest average phenotypic values in the character of PH, LL and HF, while the BC1P2 generation performed the largest DF and WF (Table 1). As for the character of LF, the BC1P1 population had the largest phenotypic value among the four offspring generations. As for the coefficient of variation (CV), it varied from 8.11% to 16.48% in the offspring generations, indicating the offspring’s diverse phenotypic performances. BC1P1 showed the highest CV on the character of PH, LL and WF, whereas BC1P2 exhibited the largest CV on HF. Moreover, the largest CV for DF and LF appeared in the F2 generation.
Parameters
PH
LL
HF
DF
LF
WF
VP1 VP2 VF1 VF2 VE VG HB (%)
53.32 15.49 32.65 35.97 33.82 2.15 5.98
29.32 7.75 32.47 38.51 23.18 15.33 39.81
0.49 1.85 1.16 1.53 1.17 0.36 23.53
1.11 2.64 1.91 1.98 1.89 0.09 4.55
0.39 0.12 0.73 0.84 0.41 0.43 51.19
0.20 0.11 0.27 0.29 0.19 0.10 34.48
Note: The abbreviations of PH, LL, HF, DF, LF, and WF are the same as those in Table 1. VP1 variance of female parent I. ‘White and Yellow’, VP2 variance of male parent I. ‘Halston’, VF1 variance of F1 hybrids, VF2 variance of F2 hybrids, VE environmental variance, VG genotypic variance, HB broad-sense heritability.
showed an obvious skewed distribution in the BC1P1 and BC1P2 generations, while they performed multimodal distribution in the F2 generation with clear quantitative genetic characteristics, indicating a mixed major gene plus polygene genetic model for the ornamental traits in bearded iris. Furthermore, some individuals in the F2, BC1P1 and BC1P2 generations exhibited transgressive segregation for the six traits, which could provide a candidate approach to selecting superior individuals.
3.2. Broad-sense heritability of the six ornamental characters The broad-sense heritability of LF, LL and WF were all larger than 30% (Table 2). The broad-sense heritability of LF (51.19%) was the largest among the six measured characters, narrowly followed by LL (39.81%) and WF (34.48%). On the other hand, the heritability of PH and DF was smaller than 10%, being 5.98% and 4.55%, respectively. 3.3. Frequency distributions of the six traits in F2, BC1P1 and BC1P2
3.4. Selection and test for the best genetic model The frequency distributions of the six traits in the F2, BC1P1 and BC1P2 generations were presented in Fig. 2. All the six characters
The Akaike’s Information Criterion (AIC) values of the twenty-four 3
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Fig. 2. Frequency distributions of the six characters in BC1P1, BC1P2 and F2 generations. The number on the Y axis stands for the proportion of each category.
4
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Table 3 Akaike’s Information Criterion (AIC) value under 24 genetic models for the six characters. Model code
A-1 A-2 A-3 A-4 B-1 B-2 B-3 B-4 B-5 B-6 C-0 C-1 D-0 D-1 D-2 D-3 D-4 E-0 E-1 E-2 E-3 E-4 E-5 E-6
Model implication
1MG-AD 1MG-A 1MG-EAD 1MG-AEND 2MG-ADI 2MG-AD 2MG-A 2MG-EA 2MG-AED 2MG-EEAD PG-ADI PG-AD MX1-AD-ADI MX1-AD-AD MX1-A-AD MX1-EAD-AD MX1-AEND-AD MX2-ADI-ADI MX2-ADI-AD MX2-AD-AD MX2-A-AD MX2-EA-AD MX2-AED-AD MX2-EEAD-AD
AIC value
Log max-likelihood-value
PH
LL
HF
DF
LF
WF
PH
LL
HF
DF
LF
WF
700.65 703.07 698.51 714.48 693.71 696.36 715.83 704.38 700.77 698.77 694.45 710.90 693.61 702.52 702.87 709.64 710.13 701.56 692.26 715.62 696.67 709.63 711.64 709.64
688.83 697.70 688.68 705.56 681.93 672.12 715.10 699.65 690.89 688.89 678.15 701.22 675.86 702.96 686.28 695.93 683.88 685.06 678.24 701.86 673.56 695.92 697.93 695.93
350.42 348.69 347.62 343.44 342.51 353.21 355.69 348.82 349.65 349.19 348.65 355.32 351.35 365.38 355.40 357.11 357.06 355.69 336.99 363.12 349.05 357.02 359.06 357.09
358.18 366.98 370.10 360.83 359.47 363.10 372.04 367.05 372.43 370.43 357.83 363.58 359.52 370.62 368.60 368.60 366.56 370.61 356.66 374.58 364.40 368.60 370.60 368.60
273.25 271.40 273.95 276.29 269.43 277.08 278.37 271.73 276.32 274.31 278.49 279.73 278.71 283.67 281.67 281.69 281.89 286.98 280.00 287.68 272.64 281.60 283.64 281.67
257.09 319.23 234.65 307.41 207.71 235.91 335.67 331.43 223.11 282.52 235.72 255.06 205.30 250.13 250.09 251.67 251.70 211.78 215.33 257.65 247.09 249.42 253.66 251.66
−346.32 −348.54 −346.26 −354.24 −336.86 −342.18 −353.91 −349.19 −346.38 −346.38 −337.23 −348.45 −334.80 −342.26 −343.43 −346.82 −347.06 −332.78 −331.13 −346.81 −339.34 −346.82 −346.82 −346.82
−340.41 −345.85 −341.34 −349.78 −330.97 −330.06 −353.55 −346.83 −341.44 −341.45 −329.07 −343.61 −325.93 −342.48 −335.14 −339.96 −333.94 −324.53 −324.12 −339.93 −327.78 −339.96 −339.96 −339.96
−171.21 −171.34 −170.81 −168.72 −161.25 −170.60 −173.84 −171.41 −170.82 −171.60 −164.33 −170.66 −163.68 −173.69 −169.70 −170.56 −170.53 −159.85 −153.49 −170.56 −165.53 −170.51 −170.53 −170.54
−175.09 −180.49 −182.05 −177.41 −169.73 −175.55 −182.02 −180.53 −182.21 −182.21 −168.91 −174.79 −167.76 −176.31 −176.30 −176.30 −175.28 −167.31 −163.33 −176.29 −173.20 −176.30 −176.30 −176.30
−132.63 −132.70 −133.98 −135.14 −124.72 −132.54 −135.19 −132.86 −134.16 −134.16 −129.25 −132.87 −127.35 −132.84 −132.84 −132.84 −132.94 −125.49 −125.00 −132.84 −127.32 −132.80 −132.82 −132.83
−124.55 −156.61 −114.33 −150.70 −93.85 −111.95 −163.83 −162.71 −107.56 −138.26 −107.86 −120.53 −90.65 −116.06 −117.04 −117.84 −117.85 −87.89 −92.67 −117.82 −114.54 −116.71 −117.83 −117.83
Note: The abbreviations of PH, LL, HF, DF, LF, and WF are the same as those in Table 1. The AIC values of candidate genetic models are bold and underlined.
while the first major gene contributed more additive effects than the second one to the character of LF. For the dominant effects (ha and hb) in PH, DF and LF, the first major gene contributed more than the second major gene, while the second major gene generated more dominant effects than the first major gene to the character of HF. For the epistatic effects, the interactions of additive × additive (i), dominance × dominance (l), additive × dominance (jab) and dominance × additive (jba) between two major genes were evident. For additive interactions, PH performed the most significant additive × additive effects (i = 6.08) among all the tested six characters. With respect to dominance interactions, PH had the largest inhibitive dominance × dominance effect (l = −5.65), while the positive dominance × dominance effects were the largest in the character of HF (l = 3.79). The additive × dominance interaction effect (jab) of PH was −7.95, while the corresponding dominance × additive interaction effect (jba) was −7.97. The narrow gap suggested the two major genes had almost the same inhibitive effects for PH. The second-order genetic parameters of the optimal model about the six characters were listed in Table 6. Except for WF, the major-gene heritability of the six tested characters were all larger than the polygene heritability, indicating that these five characters were mainly controlled by major genes and slightly modified by polygenes. The four floral characters, HF, DF, LF and WF, all performed the largest major-gene heritability in the F2 generation, which suggested that the selection of these four floral characters would be more effective in F2. The polygene heritability of WF was larger than the corresponding part of major gene, and BC1P2 performed the highest polygene heritability, which revealed the strong polygene effects from the male parent I. ‘Halston’.
genetic models for the six characters were presented in Table 3. The models with smaller AIC values would be listed as one of the optimal models, and several candidate models were selected for the six traits. As a result, D-0 and E-1 were chosen for PH; B-2 and E-3 were chosen for LL; B-1 and E-1 were chosen for HF; C-0 and E-1 were chosen for DF; A2 and B-1 were chosen for LF; while B-1 and D-0 were chosen for WF. Furthermore, goodness-of-fit test was carried out to the candidate genetic models (Table 4). The best genetic models were selected after a series of tests including Uniformity test (U21, U22 and U23), Smirnov test (nW2) and Kolmogorov test (Dn). The one with the minimum number of values below statistical significance (marked with “*” in Table 4) was chosen as the optimal model. However, if there were no significant differences among the candidate models, the one with the smallest AIC value should be chosen. For LL, the number of values below the statistical significant level in B-2 and E-3 were 4 and 0, respectively, indicating that the inheritance of LL was in accordance with an additive major gene plus additive-dominance polygene genetic model (E-3). Furthermore, E-1 was the best model for the character of PH, HF and DF, implying that these three traits were consistent with an additivedominance-epistasis major gene plus additive-dominance polygene genetic model. In addition, WF was in accordance with an additivedominance major gene plus additive-dominance-epistasis polygene genetic model (D-0). Unlike the other five characters, LF was followed by an additive-dominance-epistasis major gene genetic model (B-1), without polygene effect.
3.5. Estimation of genetic parameters for the best genetic model The first-order parameters of the best genetic model about the six characters were presented in Table 5. There existed additive-dominance effect of one major gene in WF, while the additive, dominance or epistasis effects of two major genes were observed in the other five characters. For the additive effects of PH, HF and DF, there is a relation |da|= |db|, which indicated the equal additive effects of the first and second major gene. Moreover, the additive effects of the second major gene were larger than those of the first major gene in the character of LL,
4. Discussion Improving ornamental value is one of the most important objectives in the breeding of landscape plants (Austin, 2005; Yuval et al., 2002). The floral characters (HF, DF, LF and WF), as well as plant height and leaf length are the characters most related to aesthetic values in bearded iris. For bearded iris, those with larger flowers will have a promising utilization in gardens (Guo, 2000). Although there have been 5
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Table 4 Test for goodness-of-fit of the candidate genetic models. Trait
Model code
Generation
U21
U22
U23
nW
PH
D-0
P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2
0.04(0.85) 0.00(0.96) 0.00(0.99) 0.07(0.79) 0.06(0.81) 0.25(0.62) 0.06(0.80) 0.07(0.80) 0.00(0.96) 1.15(0.28) 0.09(0.76) 0.20(0.66) 0.47(0.49) 5.64(0.02)* 0.39(0.53) 0.78(0.38) 0.05(0.82) 1.65(0.20) 0.25(0.62) 1.39(0.24) 0.01(0.94) 0.55(0.46) 0.03(0.87) 1.64(0.20) 0.05(0.82) 0.02(0.88) 0.05(0.82) 0.08(0.78) 0.01(0.93) 0.07(0.80) 0.04(0.83) 0.01(0.93) 0.01(0.91) 0.00(0.99) 0.03(0.86) 0.02(0.88) 0.00(0.95) 0.07(0.80) 0.09(0.77) 0.01(0.92) 2.90(0.09) 0.79(0.37) 0.08(0.78) 0.00(0.95) 0.00(0.97) 0.00(0.98) 0.02(0.89) 0.00(0.98) 3.22(0.07) 6.31(0.01)* 1.47(0.22) 0.03(0.86) 2.14(0.14) 0.24(0.63) 0.00(0.95) 1.29(0.26) 0.00(0.98) 0.07(0.79) 0.18(0.67) 0.00(0.99) 0.02(0.89) 5.89(0.02)* 0.02(0.90) 0.10(0.75) 0.06(0.80) 0.11(0.74) 0.03(0.87) 0.05(0.82) 0.01(0.90) 0.00(0.97) 0.00(0.99) 0.21(0.65)
0.01(0.90) 0.00(0.99) 0.02(0.90) 0.03(0.87) 0.01(0.91) 0.08(0.78) 0.03(0.86) 0.09(0.77) 0.00(0.95) 1.78(0.18) 0.03(0.86) 0.18(0.67) 0.51(0.48) 4.28(0.04)* 0.49(0.48) 1.54(0.21) 0.03(0.85) 0.81(0.37) 0.28(0.60) 1.41(0.23) 0.02(0.88) 1.33(0.25) 0.03(0.87) 0.91(0.34) 0.02(0.89) 0.01(0.93) 0.07(0.79) 0.17(0.68) 0.00(0.96) 0.14(0.71) 0.07(0.79) 0.01(0.90) 0.01(0.94) 0.00(0.99) 0.00(0.99) 0.07(0.80) 0.02(0.90) 0.03(0.86) 0.08(0.78) 0.06(0.81) 2.53(0.11) 0.35(0.55) 0.04(0.83) 0.00(0.97) 0.01(0.94) 0.01(0.94) 0.00(0.99) 0.05(0.83) 2.85(0.09) 4.39(0.04)* 1.21(0.27) 0.01(0.94) 2.28(0.13) 0.14(0.71) 0.01(0.92) 1.28(0.26) 0.00(0.97) 0.21(0.65) 0.31(0.58) 0.02(0.89) 0.01(0.90) 4.41(0.04)* 0.00(0.99) 0.28(0.60) 0.30(0.59) 0.00(0.96) 0.02(0.89) 0.02(0.88) 0.00(0.99) 0.00(1.00) 0.05(0.83) 0.24(0.62)
0.07(0.79) 0.02(0.88) 0.21(0.65) 0.15(0.70) 0.21(0.65) 0.62(0.43) 0.06(0.80) 0.03(0.87) 0.20(0.65) 1.42(0.23) 0.25(0.62) 0.00(0.98) 0.04(0.85) 0.86(0.36) 0.15(0.70) 2.40(0.12) 0.02(0.90) 1.87(0.17) 0.03(0.86) 0.04(0.84) 0.11(0.74) 3.08(0.08) 0.00(0.96) 1.31(0.25) 0.09(0.76) 0.06(0.80) 0.03(0.86) 0.33(0.56) 0.02(0.89) 0.28(0.60) 0.06(0.80) 0.03(0.87) 0.03(0.87) 0.01(0.93) 0.40(0.52) 0.20(0.66) 0.08(0.78) 0.08(0.77) 0.00(0.98) 0.33(0.57) 0.05(0.82) 1.14(0.29) 0.06(0.80) 0.18(0.67) 0.02(0.88) 0.03(0.85) 0.37(0.54) 0.91(0.34) 0.04(0.84) 1.82(0.18) 0.09(0.77) 0.14(0.71) 0.14(0.71) 0.15(0.70) 0.41(0.52) 0.02(0.90) 0.05(0.82) 0.67(0.41) 0.34(0.56) 0.34(0.56) 0.00(0.96) 0.99(0.32) 0.28(0.60) 0.79(0.37) 1.49(0.22) 2.17(0.14) 0.00(0.95) 0.07(0.79) 0.28(0.60) 0.01(0.91) 0.67(0.41) 0.05(0.83)
0.05(0.88) 0.02(0.99) 0.03(0.96) 0.04(0.95) 0.06(0.84) 0.16(0.36) 0.05(0.86) 0.03(0.99) 0.03(0.96) 0.18(0.31) 0.04(0.96) 0.04(0.92) 0.07(0.75) 0.62(0.02)* 0.07(0.78) 0.18(0.32) 0.02(0.99) 0.30(0.15) 0.05(0.86) 0.20(0.26) 0.03(0.98) 0.17(0.34) 0.02(1.00) 0.26(0.18) 0.06(0.80) 0.03(0.97) 0.07(0.79) 0.05(0.87) 0.04(0.93) 0.05(0.85) 0.06(0.79) 0.04(0.96) 0.06(0.82) 0.02(1.00) 0.05(0.86) 0.05(0.90) 0.03(0.97) 0.08(0.69) 0.06(0.84) 0.04(0.95) 0.35(0.11) 0.29(0.15) 0.04(0.95) 0.07(0.75) 0.04(0.94) 0.02(1.00) 0.05(0.85) 0.11(0.56) 0.40(0.07) 0.65(0.02)* 0.15(0.39) 0.04(0.95) 0.26(0.19) 0.09(0.65) 0.08(0.73) 0.15(0.38) 0.02(1.00) 0.05(0.90) 0.11(0.57) 0.06(0.83) 0.06(0.83) 0.63(0.02)* 0.07(0.75) 0.07(0.73) 0.08(0.71) 0.11(0.57) 0.06(0.82) 0.07(0.77) 0.07(0.76) 0.05(0.86) 0.05(0.85) 0.12(0.50)
E-1
LL
B-2
E-3
HF
B-1
E-1
DF
C-0
E-1
LF
A-2
B-1
WF
B-1
D-0
Note: The abbreviations of PH, LL, HF, DF, LF, and WF are the same as those in Table 1.
6
2
Dn 0.11(1.00) 0.10(1.00) 0.05(1.00) 0.04(1.00) 0.03(1.00) 0.06(1.00) 0.11(1.00) 0.13(1.00) 0.05(1.00) 0.07(1.00) 0.03(1.00) 0.03(1.00) 0.06(1.00) 0.67(0.01)* 0.05(1.00) 0.10(0.93) 0.03(1.00) 0.03(1.00) 0.06(1.00) 0.45(0.20) 0.08(1.00) 0.08(0.99) 0.03(1.00) 0.02(1.00) 0.07(1.00) 0.18(0.99) 0.05(1.00) 0.03(1.00) 0.04(1.00) 0.03(1.00) 0.06(1.00) 0.17(1.00) 0.06(1.00) 0.03(1.00) 0.05(1.00) 0.04(1.00) 0.09(1.00) 0.23(0.89) 0.08(1.00) 0.03(1.00) 0.03(1.00) 0.04(1.00) 0.11(1.00) 0.26(0.81) 0.09(1.00) 0.02(1.00) 0.04(1.00) 0.04(1.00) 0.12(1.00) 0.59(0.03)* 0.13(0.94) 0.06(1.00) 0.02(1.00) 0.04(1.00) 0.07(1.00) 0.32(0.58) 0.07(1.00) 0.09(0.99) 0.03(1.00) 0.04(1.00) 0.06(1.00) 0.66(0.01)* 0.09(1.00) 0.07(1.00) 0.02(1.00) 0.04(1.00) 0.06(1.00) 0.21(0.94) 0.09(1.00) 0.03(1.00) 0.03(1.00) 0.04(1.00)
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model (E-1). The optimum genetic model for LL was E-3, while D-0 model accorded with WF. Unlike the other traits controlled by two major genes, WF was controlled by only one. Furthermore, there were no polygene effects in the inheritance of LF, which was quite different from the other characters. The identification of genetic patterns will be useful in the future QTL mapping of ornamental characters in bearded iris. The additive × additive effects (i) and additive × dominance effects (jab) were effective in the selection of target characters. The additive × additive effects (i) of PH, HF, DF and LF were all positive, indicating that these four characters could be selected in late generations (Table 5). Moreover, the additive × dominance effects (jab) of PH, DF and LF were negative, suggesting the difficulties in the early selection for these traits. Combining the analysis of i and jab, it could be concluded that the selection of PH, DF and LF was effective in late generations, while the selection of LL and WF should be carried out in early generations. According to Mather and Jinks (1982), a negative sign of these two parameters (i and jab) indicated an interaction between increasing and decreasing alleles, thus providing some evidence for the existence of dispersion in the parental genotypes. Similarly, both i and jab being negative suggested a large influence of the recessive parent (Cao et al., 2016), which did not occur in this research. In the breeding of bearded iris, we breeders should figure out the gene combination and interaction effects in the inheritance of phenotypic characters, in order to improve the efficiency of breeding programs. The major-gene heritability of the six tested characters in the F2, BC1P1 and BC1P2 generations ranged from 0.04 to 0.98, while the polygene heritability contributed little to the phenotypic variation of the six characters except for WF (Table 6). The evident discrepancies of major-gene heritability among different generations may be due to the differences of parents’ genetic background (Ye et al., 2017). The polygene heritability of WF for F2, BC1P1 and BC1P2 were much higher than those of the other characters. The underlying reason may be that WF was controlled by only one major gene, unlike the other traits being controlled by two. The phenotypic traits were controlled by interactions between genes and environmental factors (Stebbins, 1950). The foregoing broad-sense heritability analysis demonstrated that the selection of PH and DF would be effective in late generations due to the large influence from the environmental factors (Table 2). While the selection of the other characters, such as LL, HF, LF and WF, should be carried out in early generations owing to the little influence from the ambient environment. Combined with the previous analysis of i and jab, the selections of PH and DF should be carried out in late generations, while the selection of LL and WF would be effective in early generations. The identification of major genes for the six ornamental traits is the first step for molecular assisted breeding in bearded iris. Based on the phenotypic data and joint segregation analysis, the effects of major genes, polygenes and their interactions for the six ornamental characters were detected, thus providing some instructions for the improvement of ornamental traits in further breeding programs. This study laid theoretical groundwork for future molecular research and accelerated the process of bearded iris breeding. In spite of the advances made in this research, we could not locate the major genes and polygenes on a particular chromosome for now, which need indepth investigations in the future study.
Table 5 The first-order parameters of the best model for the six characters. 1st order parameter
PH
LL
HF
DF
LF
WF
da db ha hb i l jab jba ha/da hb/db
5.60 5.60 5.50 5.48 6.08 −5.65 −7.95 −7.97 0.98 0.98
−4.57 10.76 – – – – – – – –
0.57 0.57 −1.22 −1.72 0.82 3.79 1.11 −1.02 −2.14 −3.02
−0.77 −0.77 2.41 2.32 0.67 −4.12 −0.30 1.00 −3.13 −3.01
0.90 −0.42 1.79 1.13 0.53 −2.36 −0.23 0.41 1.99 −2.69
−0.07 – 0.00 – – – – – 0.00 –
Note: The abbreviations of PH, LL, HF, DF, LF, and WF are the same as those in Table 1. da additive effect of the first major gene, db additive effect of the second major gene, ha dominant effect of the first major gene, hb dominant effect of the second major gene, i additive × additive effect, l dominance × dominance effect, jab additive × dominance effect, jba dominance × additive effect. Table 6 The second-order parameters of the best model for the six characters. 2nd order parameter
Generation
σ2p
σ2mg
σ2pg
h2mg
h2pg
PH
BC1P1 BC1P2 F2 BC1P1 BC1P2 F2 BC1P1 BC1P2 F2 BC1P1 BC1P2 F2 BC1P1 BC1P2 F2 BC1P1 BC1P2 F2
60.94 28.08 35.97 62.75 22.48 38.51 1.45 2.19 1.53 1.37 0.90 1.98 0.64 0.80 0.84 0.36 0.38 0.29
39.71 19.47 14.53 43.38 3.10 19.13 1.04 1.74 1.50 1.05 0.71 1.76 0.27 0.43 0.47 0.02 0.03 0.01
0.35 0.00 0.57 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 – – – 0.15 0.57 0.08
0.65 0.69 0.40 0.69 0.14 0.50 0.72 0.79 0.98 0.77 0.79 0.89 0.43 0.54 0.56 0.04 0.04 0.05
0.01 0.00 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 – – – 0.42 0.72 0.29
LL
HF
DF
LF
WF
Note: The abbreviations of PH, LL, HF, DF, LF, and WF are the same as those in Table 1. σ2p phenotypic variance, σ2mg major gene variance, σ2pg polygene variance, h2mg major gene heritability, h2pg polygene heritability.
several reports on the flower size of bearded iris, their attention was mainly paid to the F1 generation (Azimi et al., 2018; Fan et al., 2017). Moreover, the previous researches primarily concentrated on the phenotypic values and character variations, whereas the underlying genetic factors were not concerned. In the present study, we obtained six generations and statistically analyzed their major gene and polygene effects. The analysis of gene effects for the ornamental characters will provide useful information for the improvement of ornamental values. The broad-sense heritability of LF (51.19%) and LL (39.81%) were larger than the other characters in the offspring generations (Table 2). It could be concluded that the environmental factors exerted less influence on LF and LL, and both characters could be promoted through continuous hybridization and direct selection (Paramesh et al., 2014). According to the classification method described by Fogaca et al. (2012), heritability at individual level could be considered low when it was less than 0.15. The low broad-sense heritability in PH (5.98%) and DF (4.55%) suggested that the performances of plant height and flower diameter in bearded iris had compact association with the external environment, and the appropriate environment would help promote these two characters. The inheritance and gene effects of the six ornamental characters in bearded iris were investigated through joint segregation analysis. Three ornamental characters, PH, HF and DF, all suited the additive-dominance-epistasis major gene plus additive-dominance polygene genetic
Acknowledgements This research was supported by Graduate Training and Development Program of Beijing Municipal Commission of Education (BLCXY201801) and National Natural Science Fund of China(No. 31770736). We also thank Lu Meng and Saba Haider for the language polishing of this paper.
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Scientia Horticulturae 260 (2020) 108882
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The major gene and polygene effects of ornamental traits in bearded iris (Iris germanica) using joint segregation analysis
T
Zhuping Fan, Yike Gao⁎, Rong Liu, Xinzi Wang, Yanchao Guo, Qixiang Zhang Beijing Key Laboratory of Ornamental Plants Germplasm Innovation & Molecular Breeding, National Engineering Research Center for Floriculture, School of Landscape Architecture, Beijing Forestry University, No. 35 Qinghua East Road, Haidian District, Beijing, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Bearded iris Heritability Ornamental traits Joint segregation analysis Major gene Polygene
Bearded iris (Iris germanica) is an indispensable horticultural perennial in the garden of spring. Therefore, improving their ornamental value is of great importance in the process of breeding. In order to find out whether the inheritance of some ornamental characters in bearded iris was controlled by major genes or polygenes, the joint segregation analysis was applied to investigate the inheritance of the six characters related to ornamental values in six generations (P1, P2, F1, F2, BC1P1 and BC1P2), including plant height (PH), leaf length (LL), height of individual flower (HF), diameter of flower (DF), length of fall (LF) and width of fall (WF). The six tested characters performed large range of coefficient of variation in the offspring generations, from 8.11% to 16.48%, indicating the diversity of offspring’s phenotypic performances. The broad-sense heritability ranged from 4.55% (DF) to 51.19% (LF), suggesting the different ability to pass down these characters to the next generation. From the analysis follows the corollary that PH, HF and DF were all in accordance with the additive-dominanceepistasis major gene plus additive-dominance polygene genetic model (E-1). The optimum model for LL was the additive major gene plus additive-dominance polygene genetic model (E-3), while an additive-dominance major gene plus additive-dominance-epistasis polygene genetic model (D-0) was suitable for WF. Unlike the other five characters, LF accorded with the B-1 model, which was controlled by two major genes without polygene effect. It proved that the selection of LL and WF was more effective in early generations, while the selection of PH and DF would be more useful in late generations. This research shed some light on the inheritance pattern of ornamental characters in bearded iris, and laid solid foundation for further molecular breeding of ornamental plants.
1. Introduction Bearded iris (Iris germanica) refers to the large hybrid population in the Iris genus, which is characterized by thick, bushy ‘beard’ on three falls (lower petals). Their attractive appearance, ease of cultivation and propagation make them extraordinary prevalent and of great commercial value (Harkess et al., 2010; Li et al., 2016; Zhao et al., 2016). Bearded irises are among the most popular and indispensable landscape plants in the spring garden. Therefore, improving their aesthetic values has always drawn many iris breeders’ attention (Azimi et al., 2018; Bo et al., 2017). The ornamental characters, such as plant height (PH), leaf length (LL), height of individual flower (HF), diameter of flower (DF), length of fall (LF) and width of fall (WF), are closely related to their aesthetic values. However, due to the lack of hybrid populations and effective analysis method, it remains ambiguous whether the ornamental characters are controlled by major gene or polygene effects. As a result, the new cultivars with high ornamental values are primarily
⁎
produced after a large amount of labour-wasting and time-consuming hybridization practice without explicit purpose (Austin, 2005). Therefore, systematic and scientific researches are essential to decipher the in-depth inheritance patterns of ornamental characters in bearded iris (Guo, 2000). Numerous studies have focused on the inheritance of floral characters in iris, most of which paid attention to heritability. It was found in Iris hybrids that standard width, standard height and flower size showed high broad-sense heritability values (97%), indicating that these characters could be considered as useful traits in Iris hybrids selection (Azimi et al., 2018). Similarly, in our previous study (Fan et al., 2017), fourteen F1 generations were generated and the largest heritability (91.47%) was observed in the character of WF (width of fall). Besides the heritability analysis, our previous research about offspring of bearded iris cultivar ‘Halston’ and ‘White and Yellow’ showed that the fall would become slimmer in late generations such as BC1P2 (Fan et al., 2018). It is worth mentioning that the ectopic expression of
Corresponding author. E-mail address: [email protected] (Y. Gao).
https://doi.org/10.1016/j.scienta.2019.108882 Received 31 May 2019; Received in revised form 22 September 2019; Accepted 24 September 2019 0304-4238/ © 2019 Elsevier B.V. All rights reserved.
Scientia Horticulturae 260 (2020) 108882
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phytoene synthase gene (crtB) in I. germanica pink cultivar ‘Fire Bride’ could cause several flower parts to develop different degrees of novel orange and pink colors, but failed to generate red flowers (Jeknic et al., 2014). The foregoing researches were trying to reveal the inheritance essence of ornamental traits in iris, but they only unveiled a few profiles owing to the complexity of inheritance patterns. In this research, we explored whether the ornamental characters were controlled by major genes or polygenes, which could provide more information about their inheritance patterns. To the best of our knowledge, this is the first report on the inheritance patterns for ornamental characters in bearded iris. Joint segregation analysis (JSA) is a statistical method to identify the complex genetic model of quantitative characters even without molecular data (Wang and Gai, 2001). Using this method, the major genes and polygenes which controlled the target characters could be detected in multiple populations. Apart from quantitative trait locus (QTL) mapping and genome-wide association study (GWAS), JSA was an alternative method to identify a quantitative trait locus with large genetic effects without the aid of marker information. This method has been widely acknowledged in the research of vegetables, including soybean (Wang and Gai, 2001), chickpea (Anbessa et al., 2006), wheat (Khan et al., 2012), melon (Qi et al., 2015) and Brassica (Cao et al., 2016; Zhang et al., 2010). Recently, the JSA method has been gradually applied in ornamental plants such as crape myrtle (Ye et al., 2017) and chrysanthemum (Song et al., 2018). However, the JSA method has not been employed in the genetic analysis of bearded iris. In this research, the major gene and polygene effects of six ornamental characters were investigated using joint segregation analysis. The objectives of this study were to better understand the genetic mechanisms which controlled the six ornamental characters in bearded iris, and to lay the groundwork for the future development of molecular markers related to ornamental characters. The results may shed some light on breeding more bearded irises with high aesthetic values.
2.2. Field experiment To avoid contamination from other pollens, artificial emasculation was carried out the day before full bloom, and the flowers were covered with bags after artificial pollination. In 2013, the F1 generation (220 individuals) were obtained. In the blooming season of 2015, the F1 generation were used to produce F2 generation (216 individuals) by strictly self-pollination and were backcrossed with two parents to generate BC1P1 generation (212 individuals) and BC1P2 generation (236 individuals). In each generation’s first blooming year, sixty individuals were randomly selected, and six ornamental characters were measured, including plant height (PH), leaf length (LL), height of individual flower (HF), diameter of flower (DF), length of fall (LF) and width of fall (WF).
2.3. Statistical analysis The six ornamental characters were measured in the F1, F2, BC1P1, BC1P2, female parent (P1) and male parent (P2) populations. The descriptive statistical analysis and frequency distribution histogram were generated through SPSS Statistics 18.0 program. The broad-sense heritability was estimated as the ratio of genotypic variance to the phenotypic variance, just as described by Kelly and Bliss (1975), in which HB represents the broad-sense heritability, and V represents the variance of each generation:
HB (%) =
VF2 − (VP1 + VP2 + VF1) ∕3 × 100%. VF2
2.4. Joint segregation analysis The joint segregation analysis was performed on the basis of phenotypic data from the six generations (P1, P2, F1, F2, BC1P1 and BC1P2) according to the method of Gai and Wang (1998). The phenotypic values were analyzed under the twenty-four genetic models, including one major gene (A), two major genes (B), polygene (C), one major gene plus polygene (D) and two major genes plus polygene (E). According to Akaike’s Information Criterion (AIC) (Akaike, 1977), the models with smaller AIC values were considered as the candidates for the best-fit model. Then a series of statistical tests, including Uniformity test (U21, U22 and U23), Smirnov test (nW2) and Kolmogorov test (Dn), were carried out on the candidate models, in order to check the accuracy (Wang and Gai, 1997). Finally, the first and second order genetic parameters were calculated from the evaluation of component distributions in the optimal genetic model. The SEA software (Cao et al., 2013) was used to analyze the segregation genetic parameters of the six generations in this research.
2. Materials and methods 2.1. Plant materials The bearded iris cultivar Iris ‘White and Yellow’ was selected as the female parent, while I. ‘Halston’ was chosen to be the pollen donator (Fig. 1). The two cultivars were inbred for five generations to guarantee the homozygosity of the populations. All the plants were cultivated in a breeding nursery (40°09′N, 116°27′E) in Beijing, China. The experimental materials were given the same soil, moisture, temperature and light condition.
Fig. 1. The performances of P1 (I. ‘White and Yellow’) and P2 (I. ‘Halston’). Bar 2 cm. 2
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Table 1 Descriptive statistics of the six ornamental characters in two parents and four progeny generations. Trait
Generation
Min
Max
Mean ± SD
Variance
Skewness
Kurtosis
CV(%)
PH/cm
P1 P2 F1 F2 BC1 P1 BC1 P2
35.6 30.5 41.0 24.6 34.5 34.2
59.1 41.1 58.5 51.9 66.1 55.9
50.32 36.08 49.18 41.60 47.40 47.42
± ± ± ± ± ±
7.30 3.94 5.71 6.00 7.81 5.30
53.32 15.49 32.65 35.97 60.94 28.08
−0.86 −0.31 0.01 －0.78 0.49 −1.08
0.92 0.44 −1.23 1.39 −0.30 1.00
14.51 10.92 11.61 14.42 16.48 11.18
LL/cm
P1 P2 F1 F2 BC1 P1 BC1 P2
42.6 33.6 42.5 26.9 36.6 35.4
57.4 39.8 59.0 52.5 66.4 57.2
49.74 37.74 50.96 41.10 48.27 48.13
± ± ± ± ± ±
5.41 2.78 5.70 6.21 7.92 4.74
29.32 7.75 32.47 38.51 62.75 22.48
0.26 −1.04 −0.02 −0.75 0.37 −0.74
−1.11 −0.86 −1.17 0.48 −0.53 0.93
10.88 7.37 11.19 15.11 16.41 9.85
HF/cm
P1 P2 F1 F2 BC1 P1 BC1 P2
9.5 9.1 9.1 6.2 7.0 6.4
11.9 12.3 12.3 11.8 11.9 12.6
10.76 ± 0.70 10.45 ± 1.36 10.57 ± 1.08 9.55 ± 1.24 9.94 ± 1.20 9.50 ± 1.48
0.49 1.85 1.16 1.53 1.45 2.19
−0.06 0.98 0.16 −0.42 −0.61 −0.45
0.55 1.23 −0.80 1.13 0.07 0.21
6.51 13.01 10.22 12.98 12.07 15.58
DF/cm
P1 P2 F1 F2 BC1 P1 BC1 P2
7.8 7.6 8.4 8.6 9.5 9.6
10.9 11.5 13.2 13.8 14.5 14.3
9.49 ± 1.05 10.32 ± 1.63 11.25 ± 1.38 11.24 ± 1.41 11.67 ± 1.17 11.71 ± 0.95
1.11 2.64 1.91 1.98 1.37 0.90
−0.22 −1.62 −0.76 −0.16 0.22 0.07
−1.12 2.52 −0.09 −0.80 0.36 2.05
11.06 15.79 12.27 12.54 10.03 8.11
LF/cm
P1 P2 F1 F2 BC1 P1 BC1 P2
6.5 6.0 5.6 4.8 6.5 6.0
8.8 6.9 8.5 8.9 9.5 9.9
7.70 6.54 7.23 7.51 8.09 7.44
± ± ± ± ± ±
0.62 0.35 0.85 0.92 0.80 0.89
0.39 0.12 0.73 0.84 0.64 0.80
−0.28 −0.90 −0.30 −0.93 −0.05 0.97
1.81 0.79 －0.73 1.78 −1.60 0.99
8.05 5.35 11.76 12.25 9.89 11.96
WF/cm
P1 P2 F1 F2 BC1 P1 BC1 P2
4.5 5.2 4.2 3.7 4.2 3.9
5.8 6.0 5.5 6.0 6.3 6.4
5.08 5.74 4.81 5.02 5.19 5.46
± ± ± ± ± ±
0.45 0.33 0.52 0.54 0.60 0.62
0.20 0.11 0.27 0.29 0.36 0.38
0.54 −1.43 0.31 −0.24 0.01 −0.49
−0.67 2.09 −1.55 0.31 −1.04 0.12
8.86 5.75 10.81 10.76 11.56 11.36
Note: PH plant height, LL leaf length, HF height of individual flower, DF diameter of flower, LF length of fall, WF width of fall.
3. Results
Table 2 Broad-sense heritability of six measured ornamental characters.
3.1. Descriptive statistics of the phenotypic data The F1 generation had the largest average phenotypic values in the character of PH, LL and HF, while the BC1P2 generation performed the largest DF and WF (Table 1). As for the character of LF, the BC1P1 population had the largest phenotypic value among the four offspring generations. As for the coefficient of variation (CV), it varied from 8.11% to 16.48% in the offspring generations, indicating the offspring’s diverse phenotypic performances. BC1P1 showed the highest CV on the character of PH, LL and WF, whereas BC1P2 exhibited the largest CV on HF. Moreover, the largest CV for DF and LF appeared in the F2 generation.
Parameters
PH
LL
HF
DF
LF
WF
VP1 VP2 VF1 VF2 VE VG HB (%)
53.32 15.49 32.65 35.97 33.82 2.15 5.98
29.32 7.75 32.47 38.51 23.18 15.33 39.81
0.49 1.85 1.16 1.53 1.17 0.36 23.53
1.11 2.64 1.91 1.98 1.89 0.09 4.55
0.39 0.12 0.73 0.84 0.41 0.43 51.19
0.20 0.11 0.27 0.29 0.19 0.10 34.48
Note: The abbreviations of PH, LL, HF, DF, LF, and WF are the same as those in Table 1. VP1 variance of female parent I. ‘White and Yellow’, VP2 variance of male parent I. ‘Halston’, VF1 variance of F1 hybrids, VF2 variance of F2 hybrids, VE environmental variance, VG genotypic variance, HB broad-sense heritability.
showed an obvious skewed distribution in the BC1P1 and BC1P2 generations, while they performed multimodal distribution in the F2 generation with clear quantitative genetic characteristics, indicating a mixed major gene plus polygene genetic model for the ornamental traits in bearded iris. Furthermore, some individuals in the F2, BC1P1 and BC1P2 generations exhibited transgressive segregation for the six traits, which could provide a candidate approach to selecting superior individuals.
3.2. Broad-sense heritability of the six ornamental characters The broad-sense heritability of LF, LL and WF were all larger than 30% (Table 2). The broad-sense heritability of LF (51.19%) was the largest among the six measured characters, narrowly followed by LL (39.81%) and WF (34.48%). On the other hand, the heritability of PH and DF was smaller than 10%, being 5.98% and 4.55%, respectively. 3.3. Frequency distributions of the six traits in F2, BC1P1 and BC1P2
3.4. Selection and test for the best genetic model The frequency distributions of the six traits in the F2, BC1P1 and BC1P2 generations were presented in Fig. 2. All the six characters
The Akaike’s Information Criterion (AIC) values of the twenty-four 3
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Fig. 2. Frequency distributions of the six characters in BC1P1, BC1P2 and F2 generations. The number on the Y axis stands for the proportion of each category.
4
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Table 3 Akaike’s Information Criterion (AIC) value under 24 genetic models for the six characters. Model code
A-1 A-2 A-3 A-4 B-1 B-2 B-3 B-4 B-5 B-6 C-0 C-1 D-0 D-1 D-2 D-3 D-4 E-0 E-1 E-2 E-3 E-4 E-5 E-6
Model implication
1MG-AD 1MG-A 1MG-EAD 1MG-AEND 2MG-ADI 2MG-AD 2MG-A 2MG-EA 2MG-AED 2MG-EEAD PG-ADI PG-AD MX1-AD-ADI MX1-AD-AD MX1-A-AD MX1-EAD-AD MX1-AEND-AD MX2-ADI-ADI MX2-ADI-AD MX2-AD-AD MX2-A-AD MX2-EA-AD MX2-AED-AD MX2-EEAD-AD
AIC value
Log max-likelihood-value
PH
LL
HF
DF
LF
WF
PH
LL
HF
DF
LF
WF
700.65 703.07 698.51 714.48 693.71 696.36 715.83 704.38 700.77 698.77 694.45 710.90 693.61 702.52 702.87 709.64 710.13 701.56 692.26 715.62 696.67 709.63 711.64 709.64
688.83 697.70 688.68 705.56 681.93 672.12 715.10 699.65 690.89 688.89 678.15 701.22 675.86 702.96 686.28 695.93 683.88 685.06 678.24 701.86 673.56 695.92 697.93 695.93
350.42 348.69 347.62 343.44 342.51 353.21 355.69 348.82 349.65 349.19 348.65 355.32 351.35 365.38 355.40 357.11 357.06 355.69 336.99 363.12 349.05 357.02 359.06 357.09
358.18 366.98 370.10 360.83 359.47 363.10 372.04 367.05 372.43 370.43 357.83 363.58 359.52 370.62 368.60 368.60 366.56 370.61 356.66 374.58 364.40 368.60 370.60 368.60
273.25 271.40 273.95 276.29 269.43 277.08 278.37 271.73 276.32 274.31 278.49 279.73 278.71 283.67 281.67 281.69 281.89 286.98 280.00 287.68 272.64 281.60 283.64 281.67
257.09 319.23 234.65 307.41 207.71 235.91 335.67 331.43 223.11 282.52 235.72 255.06 205.30 250.13 250.09 251.67 251.70 211.78 215.33 257.65 247.09 249.42 253.66 251.66
−346.32 −348.54 −346.26 −354.24 −336.86 −342.18 −353.91 −349.19 −346.38 −346.38 −337.23 −348.45 −334.80 −342.26 −343.43 −346.82 −347.06 −332.78 −331.13 −346.81 −339.34 −346.82 −346.82 −346.82
−340.41 −345.85 −341.34 −349.78 −330.97 −330.06 −353.55 −346.83 −341.44 −341.45 −329.07 −343.61 −325.93 −342.48 −335.14 −339.96 −333.94 −324.53 −324.12 −339.93 −327.78 −339.96 −339.96 −339.96
−171.21 −171.34 −170.81 −168.72 −161.25 −170.60 −173.84 −171.41 −170.82 −171.60 −164.33 −170.66 −163.68 −173.69 −169.70 −170.56 −170.53 −159.85 −153.49 −170.56 −165.53 −170.51 −170.53 −170.54
−175.09 −180.49 −182.05 −177.41 −169.73 −175.55 −182.02 −180.53 −182.21 −182.21 −168.91 −174.79 −167.76 −176.31 −176.30 −176.30 −175.28 −167.31 −163.33 −176.29 −173.20 −176.30 −176.30 −176.30
−132.63 −132.70 −133.98 −135.14 −124.72 −132.54 −135.19 −132.86 −134.16 −134.16 −129.25 −132.87 −127.35 −132.84 −132.84 −132.84 −132.94 −125.49 −125.00 −132.84 −127.32 −132.80 −132.82 −132.83
−124.55 −156.61 −114.33 −150.70 −93.85 −111.95 −163.83 −162.71 −107.56 −138.26 −107.86 −120.53 −90.65 −116.06 −117.04 −117.84 −117.85 −87.89 −92.67 −117.82 −114.54 −116.71 −117.83 −117.83
Note: The abbreviations of PH, LL, HF, DF, LF, and WF are the same as those in Table 1. The AIC values of candidate genetic models are bold and underlined.
while the first major gene contributed more additive effects than the second one to the character of LF. For the dominant effects (ha and hb) in PH, DF and LF, the first major gene contributed more than the second major gene, while the second major gene generated more dominant effects than the first major gene to the character of HF. For the epistatic effects, the interactions of additive × additive (i), dominance × dominance (l), additive × dominance (jab) and dominance × additive (jba) between two major genes were evident. For additive interactions, PH performed the most significant additive × additive effects (i = 6.08) among all the tested six characters. With respect to dominance interactions, PH had the largest inhibitive dominance × dominance effect (l = −5.65), while the positive dominance × dominance effects were the largest in the character of HF (l = 3.79). The additive × dominance interaction effect (jab) of PH was −7.95, while the corresponding dominance × additive interaction effect (jba) was −7.97. The narrow gap suggested the two major genes had almost the same inhibitive effects for PH. The second-order genetic parameters of the optimal model about the six characters were listed in Table 6. Except for WF, the major-gene heritability of the six tested characters were all larger than the polygene heritability, indicating that these five characters were mainly controlled by major genes and slightly modified by polygenes. The four floral characters, HF, DF, LF and WF, all performed the largest major-gene heritability in the F2 generation, which suggested that the selection of these four floral characters would be more effective in F2. The polygene heritability of WF was larger than the corresponding part of major gene, and BC1P2 performed the highest polygene heritability, which revealed the strong polygene effects from the male parent I. ‘Halston’.
genetic models for the six characters were presented in Table 3. The models with smaller AIC values would be listed as one of the optimal models, and several candidate models were selected for the six traits. As a result, D-0 and E-1 were chosen for PH; B-2 and E-3 were chosen for LL; B-1 and E-1 were chosen for HF; C-0 and E-1 were chosen for DF; A2 and B-1 were chosen for LF; while B-1 and D-0 were chosen for WF. Furthermore, goodness-of-fit test was carried out to the candidate genetic models (Table 4). The best genetic models were selected after a series of tests including Uniformity test (U21, U22 and U23), Smirnov test (nW2) and Kolmogorov test (Dn). The one with the minimum number of values below statistical significance (marked with “*” in Table 4) was chosen as the optimal model. However, if there were no significant differences among the candidate models, the one with the smallest AIC value should be chosen. For LL, the number of values below the statistical significant level in B-2 and E-3 were 4 and 0, respectively, indicating that the inheritance of LL was in accordance with an additive major gene plus additive-dominance polygene genetic model (E-3). Furthermore, E-1 was the best model for the character of PH, HF and DF, implying that these three traits were consistent with an additivedominance-epistasis major gene plus additive-dominance polygene genetic model. In addition, WF was in accordance with an additivedominance major gene plus additive-dominance-epistasis polygene genetic model (D-0). Unlike the other five characters, LF was followed by an additive-dominance-epistasis major gene genetic model (B-1), without polygene effect.
3.5. Estimation of genetic parameters for the best genetic model The first-order parameters of the best genetic model about the six characters were presented in Table 5. There existed additive-dominance effect of one major gene in WF, while the additive, dominance or epistasis effects of two major genes were observed in the other five characters. For the additive effects of PH, HF and DF, there is a relation |da|= |db|, which indicated the equal additive effects of the first and second major gene. Moreover, the additive effects of the second major gene were larger than those of the first major gene in the character of LL,
4. Discussion Improving ornamental value is one of the most important objectives in the breeding of landscape plants (Austin, 2005; Yuval et al., 2002). The floral characters (HF, DF, LF and WF), as well as plant height and leaf length are the characters most related to aesthetic values in bearded iris. For bearded iris, those with larger flowers will have a promising utilization in gardens (Guo, 2000). Although there have been 5
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Table 4 Test for goodness-of-fit of the candidate genetic models. Trait
Model code
Generation
U21
U22
U23
nW
PH
D-0
P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2 P1 P2 F1 F2 BC1P1 BC1P2
0.04(0.85) 0.00(0.96) 0.00(0.99) 0.07(0.79) 0.06(0.81) 0.25(0.62) 0.06(0.80) 0.07(0.80) 0.00(0.96) 1.15(0.28) 0.09(0.76) 0.20(0.66) 0.47(0.49) 5.64(0.02)* 0.39(0.53) 0.78(0.38) 0.05(0.82) 1.65(0.20) 0.25(0.62) 1.39(0.24) 0.01(0.94) 0.55(0.46) 0.03(0.87) 1.64(0.20) 0.05(0.82) 0.02(0.88) 0.05(0.82) 0.08(0.78) 0.01(0.93) 0.07(0.80) 0.04(0.83) 0.01(0.93) 0.01(0.91) 0.00(0.99) 0.03(0.86) 0.02(0.88) 0.00(0.95) 0.07(0.80) 0.09(0.77) 0.01(0.92) 2.90(0.09) 0.79(0.37) 0.08(0.78) 0.00(0.95) 0.00(0.97) 0.00(0.98) 0.02(0.89) 0.00(0.98) 3.22(0.07) 6.31(0.01)* 1.47(0.22) 0.03(0.86) 2.14(0.14) 0.24(0.63) 0.00(0.95) 1.29(0.26) 0.00(0.98) 0.07(0.79) 0.18(0.67) 0.00(0.99) 0.02(0.89) 5.89(0.02)* 0.02(0.90) 0.10(0.75) 0.06(0.80) 0.11(0.74) 0.03(0.87) 0.05(0.82) 0.01(0.90) 0.00(0.97) 0.00(0.99) 0.21(0.65)
0.01(0.90) 0.00(0.99) 0.02(0.90) 0.03(0.87) 0.01(0.91) 0.08(0.78) 0.03(0.86) 0.09(0.77) 0.00(0.95) 1.78(0.18) 0.03(0.86) 0.18(0.67) 0.51(0.48) 4.28(0.04)* 0.49(0.48) 1.54(0.21) 0.03(0.85) 0.81(0.37) 0.28(0.60) 1.41(0.23) 0.02(0.88) 1.33(0.25) 0.03(0.87) 0.91(0.34) 0.02(0.89) 0.01(0.93) 0.07(0.79) 0.17(0.68) 0.00(0.96) 0.14(0.71) 0.07(0.79) 0.01(0.90) 0.01(0.94) 0.00(0.99) 0.00(0.99) 0.07(0.80) 0.02(0.90) 0.03(0.86) 0.08(0.78) 0.06(0.81) 2.53(0.11) 0.35(0.55) 0.04(0.83) 0.00(0.97) 0.01(0.94) 0.01(0.94) 0.00(0.99) 0.05(0.83) 2.85(0.09) 4.39(0.04)* 1.21(0.27) 0.01(0.94) 2.28(0.13) 0.14(0.71) 0.01(0.92) 1.28(0.26) 0.00(0.97) 0.21(0.65) 0.31(0.58) 0.02(0.89) 0.01(0.90) 4.41(0.04)* 0.00(0.99) 0.28(0.60) 0.30(0.59) 0.00(0.96) 0.02(0.89) 0.02(0.88) 0.00(0.99) 0.00(1.00) 0.05(0.83) 0.24(0.62)
0.07(0.79) 0.02(0.88) 0.21(0.65) 0.15(0.70) 0.21(0.65) 0.62(0.43) 0.06(0.80) 0.03(0.87) 0.20(0.65) 1.42(0.23) 0.25(0.62) 0.00(0.98) 0.04(0.85) 0.86(0.36) 0.15(0.70) 2.40(0.12) 0.02(0.90) 1.87(0.17) 0.03(0.86) 0.04(0.84) 0.11(0.74) 3.08(0.08) 0.00(0.96) 1.31(0.25) 0.09(0.76) 0.06(0.80) 0.03(0.86) 0.33(0.56) 0.02(0.89) 0.28(0.60) 0.06(0.80) 0.03(0.87) 0.03(0.87) 0.01(0.93) 0.40(0.52) 0.20(0.66) 0.08(0.78) 0.08(0.77) 0.00(0.98) 0.33(0.57) 0.05(0.82) 1.14(0.29) 0.06(0.80) 0.18(0.67) 0.02(0.88) 0.03(0.85) 0.37(0.54) 0.91(0.34) 0.04(0.84) 1.82(0.18) 0.09(0.77) 0.14(0.71) 0.14(0.71) 0.15(0.70) 0.41(0.52) 0.02(0.90) 0.05(0.82) 0.67(0.41) 0.34(0.56) 0.34(0.56) 0.00(0.96) 0.99(0.32) 0.28(0.60) 0.79(0.37) 1.49(0.22) 2.17(0.14) 0.00(0.95) 0.07(0.79) 0.28(0.60) 0.01(0.91) 0.67(0.41) 0.05(0.83)
0.05(0.88) 0.02(0.99) 0.03(0.96) 0.04(0.95) 0.06(0.84) 0.16(0.36) 0.05(0.86) 0.03(0.99) 0.03(0.96) 0.18(0.31) 0.04(0.96) 0.04(0.92) 0.07(0.75) 0.62(0.02)* 0.07(0.78) 0.18(0.32) 0.02(0.99) 0.30(0.15) 0.05(0.86) 0.20(0.26) 0.03(0.98) 0.17(0.34) 0.02(1.00) 0.26(0.18) 0.06(0.80) 0.03(0.97) 0.07(0.79) 0.05(0.87) 0.04(0.93) 0.05(0.85) 0.06(0.79) 0.04(0.96) 0.06(0.82) 0.02(1.00) 0.05(0.86) 0.05(0.90) 0.03(0.97) 0.08(0.69) 0.06(0.84) 0.04(0.95) 0.35(0.11) 0.29(0.15) 0.04(0.95) 0.07(0.75) 0.04(0.94) 0.02(1.00) 0.05(0.85) 0.11(0.56) 0.40(0.07) 0.65(0.02)* 0.15(0.39) 0.04(0.95) 0.26(0.19) 0.09(0.65) 0.08(0.73) 0.15(0.38) 0.02(1.00) 0.05(0.90) 0.11(0.57) 0.06(0.83) 0.06(0.83) 0.63(0.02)* 0.07(0.75) 0.07(0.73) 0.08(0.71) 0.11(0.57) 0.06(0.82) 0.07(0.77) 0.07(0.76) 0.05(0.86) 0.05(0.85) 0.12(0.50)
E-1
LL
B-2
E-3
HF
B-1
E-1
DF
C-0
E-1
LF
A-2
B-1
WF
B-1
D-0
Note: The abbreviations of PH, LL, HF, DF, LF, and WF are the same as those in Table 1.
6
2
Dn 0.11(1.00) 0.10(1.00) 0.05(1.00) 0.04(1.00) 0.03(1.00) 0.06(1.00) 0.11(1.00) 0.13(1.00) 0.05(1.00) 0.07(1.00) 0.03(1.00) 0.03(1.00) 0.06(1.00) 0.67(0.01)* 0.05(1.00) 0.10(0.93) 0.03(1.00) 0.03(1.00) 0.06(1.00) 0.45(0.20) 0.08(1.00) 0.08(0.99) 0.03(1.00) 0.02(1.00) 0.07(1.00) 0.18(0.99) 0.05(1.00) 0.03(1.00) 0.04(1.00) 0.03(1.00) 0.06(1.00) 0.17(1.00) 0.06(1.00) 0.03(1.00) 0.05(1.00) 0.04(1.00) 0.09(1.00) 0.23(0.89) 0.08(1.00) 0.03(1.00) 0.03(1.00) 0.04(1.00) 0.11(1.00) 0.26(0.81) 0.09(1.00) 0.02(1.00) 0.04(1.00) 0.04(1.00) 0.12(1.00) 0.59(0.03)* 0.13(0.94) 0.06(1.00) 0.02(1.00) 0.04(1.00) 0.07(1.00) 0.32(0.58) 0.07(1.00) 0.09(0.99) 0.03(1.00) 0.04(1.00) 0.06(1.00) 0.66(0.01)* 0.09(1.00) 0.07(1.00) 0.02(1.00) 0.04(1.00) 0.06(1.00) 0.21(0.94) 0.09(1.00) 0.03(1.00) 0.03(1.00) 0.04(1.00)
Scientia Horticulturae 260 (2020) 108882
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model (E-1). The optimum genetic model for LL was E-3, while D-0 model accorded with WF. Unlike the other traits controlled by two major genes, WF was controlled by only one. Furthermore, there were no polygene effects in the inheritance of LF, which was quite different from the other characters. The identification of genetic patterns will be useful in the future QTL mapping of ornamental characters in bearded iris. The additive × additive effects (i) and additive × dominance effects (jab) were effective in the selection of target characters. The additive × additive effects (i) of PH, HF, DF and LF were all positive, indicating that these four characters could be selected in late generations (Table 5). Moreover, the additive × dominance effects (jab) of PH, DF and LF were negative, suggesting the difficulties in the early selection for these traits. Combining the analysis of i and jab, it could be concluded that the selection of PH, DF and LF was effective in late generations, while the selection of LL and WF should be carried out in early generations. According to Mather and Jinks (1982), a negative sign of these two parameters (i and jab) indicated an interaction between increasing and decreasing alleles, thus providing some evidence for the existence of dispersion in the parental genotypes. Similarly, both i and jab being negative suggested a large influence of the recessive parent (Cao et al., 2016), which did not occur in this research. In the breeding of bearded iris, we breeders should figure out the gene combination and interaction effects in the inheritance of phenotypic characters, in order to improve the efficiency of breeding programs. The major-gene heritability of the six tested characters in the F2, BC1P1 and BC1P2 generations ranged from 0.04 to 0.98, while the polygene heritability contributed little to the phenotypic variation of the six characters except for WF (Table 6). The evident discrepancies of major-gene heritability among different generations may be due to the differences of parents’ genetic background (Ye et al., 2017). The polygene heritability of WF for F2, BC1P1 and BC1P2 were much higher than those of the other characters. The underlying reason may be that WF was controlled by only one major gene, unlike the other traits being controlled by two. The phenotypic traits were controlled by interactions between genes and environmental factors (Stebbins, 1950). The foregoing broad-sense heritability analysis demonstrated that the selection of PH and DF would be effective in late generations due to the large influence from the environmental factors (Table 2). While the selection of the other characters, such as LL, HF, LF and WF, should be carried out in early generations owing to the little influence from the ambient environment. Combined with the previous analysis of i and jab, the selections of PH and DF should be carried out in late generations, while the selection of LL and WF would be effective in early generations. The identification of major genes for the six ornamental traits is the first step for molecular assisted breeding in bearded iris. Based on the phenotypic data and joint segregation analysis, the effects of major genes, polygenes and their interactions for the six ornamental characters were detected, thus providing some instructions for the improvement of ornamental traits in further breeding programs. This study laid theoretical groundwork for future molecular research and accelerated the process of bearded iris breeding. In spite of the advances made in this research, we could not locate the major genes and polygenes on a particular chromosome for now, which need indepth investigations in the future study.
Table 5 The first-order parameters of the best model for the six characters. 1st order parameter
PH
LL
HF
DF
LF
WF
da db ha hb i l jab jba ha/da hb/db
5.60 5.60 5.50 5.48 6.08 −5.65 −7.95 −7.97 0.98 0.98
−4.57 10.76 – – – – – – – –
0.57 0.57 −1.22 −1.72 0.82 3.79 1.11 −1.02 −2.14 −3.02
−0.77 −0.77 2.41 2.32 0.67 −4.12 −0.30 1.00 −3.13 −3.01
0.90 −0.42 1.79 1.13 0.53 −2.36 −0.23 0.41 1.99 −2.69
−0.07 – 0.00 – – – – – 0.00 –
Note: The abbreviations of PH, LL, HF, DF, LF, and WF are the same as those in Table 1. da additive effect of the first major gene, db additive effect of the second major gene, ha dominant effect of the first major gene, hb dominant effect of the second major gene, i additive × additive effect, l dominance × dominance effect, jab additive × dominance effect, jba dominance × additive effect. Table 6 The second-order parameters of the best model for the six characters. 2nd order parameter
Generation
σ2p
σ2mg
σ2pg
h2mg
h2pg
PH
BC1P1 BC1P2 F2 BC1P1 BC1P2 F2 BC1P1 BC1P2 F2 BC1P1 BC1P2 F2 BC1P1 BC1P2 F2 BC1P1 BC1P2 F2
60.94 28.08 35.97 62.75 22.48 38.51 1.45 2.19 1.53 1.37 0.90 1.98 0.64 0.80 0.84 0.36 0.38 0.29
39.71 19.47 14.53 43.38 3.10 19.13 1.04 1.74 1.50 1.05 0.71 1.76 0.27 0.43 0.47 0.02 0.03 0.01
0.35 0.00 0.57 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 – – – 0.15 0.57 0.08
0.65 0.69 0.40 0.69 0.14 0.50 0.72 0.79 0.98 0.77 0.79 0.89 0.43 0.54 0.56 0.04 0.04 0.05
0.01 0.00 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 – – – 0.42 0.72 0.29
LL
HF
DF
LF
WF
Note: The abbreviations of PH, LL, HF, DF, LF, and WF are the same as those in Table 1. σ2p phenotypic variance, σ2mg major gene variance, σ2pg polygene variance, h2mg major gene heritability, h2pg polygene heritability.
several reports on the flower size of bearded iris, their attention was mainly paid to the F1 generation (Azimi et al., 2018; Fan et al., 2017). Moreover, the previous researches primarily concentrated on the phenotypic values and character variations, whereas the underlying genetic factors were not concerned. In the present study, we obtained six generations and statistically analyzed their major gene and polygene effects. The analysis of gene effects for the ornamental characters will provide useful information for the improvement of ornamental values. The broad-sense heritability of LF (51.19%) and LL (39.81%) were larger than the other characters in the offspring generations (Table 2). It could be concluded that the environmental factors exerted less influence on LF and LL, and both characters could be promoted through continuous hybridization and direct selection (Paramesh et al., 2014). According to the classification method described by Fogaca et al. (2012), heritability at individual level could be considered low when it was less than 0.15. The low broad-sense heritability in PH (5.98%) and DF (4.55%) suggested that the performances of plant height and flower diameter in bearded iris had compact association with the external environment, and the appropriate environment would help promote these two characters. The inheritance and gene effects of the six ornamental characters in bearded iris were investigated through joint segregation analysis. Three ornamental characters, PH, HF and DF, all suited the additive-dominance-epistasis major gene plus additive-dominance polygene genetic
Acknowledgements This research was supported by Graduate Training and Development Program of Beijing Municipal Commission of Education (BLCXY201801) and National Natural Science Fund of China(No. 31770736). We also thank Lu Meng and Saba Haider for the language polishing of this paper.
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Scientia Horticulturae 260 (2020) 108882
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