Onion seed germination as affected by temperature and light

International Journal of Vegetable Science

ISSN: 1931-5260 (Print) 1931-5279 (Online) Journal homepage: http://www.tandfonline.com/loi/wijv20

Onion Seed Germination as Affected by Temperature and Light Azmi Abu-Rayyan , Muhanad Walid Akash & Giorgio Gianquinto To cite this article: Azmi Abu-Rayyan , Muhanad Walid Akash & Giorgio Gianquinto (2012) Onion Seed Germination as Affected by Temperature and Light, International Journal of Vegetable Science, 18:1, 49-63, DOI: 10.1080/19315260.2011.570419 To link to this article: http://dx.doi.org/10.1080/19315260.2011.570419

Published online: 21 Dec 2011.

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Date: 04 May 2017, At: 04:10

International Journal of Vegetable Science, 18:49–63, 2012 Copyright © Taylor & Francis Group, LLC ISSN: 1931-5260 print / 1931-5279 online DOI: 10.1080/19315260.2011.570419

Onion Seed Germination as Affected by Temperature and Light Azmi Abu-Rayyan,1 Muhanad Walid Akash,1 and Giorgio Gianquinto2 1 The University of Jordan, Faculty of Agriculture, Department of Horticulture and Crop Science, Amman, Jordan 2 Alma Mater Studiorum, Universita di Bologna, Department of Agroenvironmental Science and Technology, Viale Fanin, Bologna, Italy

Producers need to know whether the germination rate will produce sufficient numbers of seedlings needed for field production of onion (Allium cepa L.). The influence of temperature (5.0, 7.5, 10, 15, 20, 25, 30, 35, or 40◦ C) and continuous light or continuous dark was tested for effects on percentage germination of normal, abnormal, or diseased seed; production of normal seedlings; and percentage of ungerminated solid and soft seeds of onion. Temperatures from 7.5 to 30◦ C generally assured a high germination percentage and a high percentage of normal seedlings. The most rapid germination occurred at 25◦ C in the dark. At 5, 35, and 40◦ C normal germination was only about 10%. The model from the Weibull function indicated that temperature influenced the time between the beginning of imbibition to germination. Onion seed exposed to temperatures between 10 and 30◦ C under field conditions could produce a high germination percentage, which should lead to development of normal seedlings.

Keywords Allium cepa, Germination, Light, Temperature, Weibull function.

Because onion (Allium cepa L.) can be cultivated from the tropics to subarctic, it is exposed to a wide range of temperatures from sowing to harvest (Food and Agriculture Organization [FAO], 2008). The correct temperature range is important for high germination, to achieve efficient crop establishment and a uniform stand, and for plants to be competitive against weeds (Brewester, 1994; Gianquinto and Pimpini, 1989).

Factors affecting germination include temperature and light (Hartemann and Kester, 1983). The three-parameter Wiebull function proved to be an efficient and flexible model for simulation of germination in which the Address correspondence to Azmi Abu-Rayyan, The University of Jordan, Faculty of Agriculture, Department of Horticulture and Crop Science, Amman 11942, Jordan.

E-mail: aburayan@ju.edu.jo

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full biological contributions of three temperature-dependent parameters are expressed (Pimpini et al., 1993). The ability to estimate time from imbibition at which germination starts, germination speed, and the progress affecting germination speed was described (Pimpini et al., 1993). This germination test used to quantify and analyze the time required to reach a specified proportion of germination at different temperature levels can be evaluated by calculating a useful index using the final germination percentage, the rate and uniformity of germination, and its adequacy in comparison to germination values as proposed by Diavanshir and Pourbeik (1976).

This procedure could be a standardized method for evaluating seed viability and effectiveness of treatments to achieve a germination rate close to the number of seedlings that needs to be established and surviving in the field (Pimpini et al., 1993). Effects of temperature and light were determined on percentage of normal, abnormal, diseased, damaged, solid, and soft seed.

MATERIALS AND METHODS The onion cvs. Bianca Giugno Musonà, Bianca Maggio Piattà, Red Creole, and Texas Grano 502 were used. The experiments were carried out in light- and temperature-controlled chambers. There were 18 treatments for each seed lot arranged in a completely randomized design with four replications. Data were obtained from the factorial combination of two light conditions (continuous photosynthetic active radiation [PAR] of 3.2 mol/m2 /d or continuous dark) and temperatures of 5, 7.5, 10, 15, 20, 25, 30, 35, or 40C◦ . The photosynthetic photon flux density inside the chambers was 37 mol/m2 ·s−1 light provided from four 18-W cool white fluorescent tubes (Osram L18/20, Lumilux, Germany).

Differences between means were examined by Scheffe’s test to protect against alpha inflation error.

Seed were placed in cell culture dishes (11.5 × 3.5 cm) on filter paper moistened with distilled water (100 seed/dish). Germinated seed were counted daily and classified as producing normal or abnormal seedlings, which were determined to be diseased, damaged, or have ungerminated solid or soft seeds. The effects of treatment on total percentage germination and percentage of normal, abnormal, diseased, damaged, solid ungerminated, and soft seeds up to 25 days after establishment were subjected to analysis of variance.

A model derived by modifying the Weibull function (Johnson and Kotz, 1970) was used to simulate germination times at different temperatures.

Model parameters were used to calculate a germination index capable of synthesizing quantity, uniformity, and rate of germination. The relationship of germination with time was studied using a functional approach, employing the three-parameter Weibull function F(x) and the derivative f (x) as described

by Pimpini et al. (1993). The Weibull function and the fitting procedure for

Onion Seed Germination

temperatures between 7.5 and 30◦ C (Bonner and Dell, 1976) were used because few seeds germinate below 7.5 or above 40◦ C, especially in light; in the dark the model was not suitable. A model derived by modifying the Weibull function: F(x) = f(x) =

1 − exp{−[(x − a)/b]c }; c/b[(x − a)/b](c−1) exp .{−[(x − a)/b]c }

a parameter, estimates the time from imbibition at which germination starts, while b has a scaling role and is related to germination speed. b is the time beyond a that is required to accomplish approximately 63% of germination). c parameter, defines the shape of the distribution.

As a function of the model and with the parameters used the following was computed: F(p, t) = a + b − loge (1 − p)1/c where the temperature dependence of a and b is expressed by the functions described above and F(p, t) is the time taken to reach a specified proportion (p) of germination for a given temperature (t).

For an objective evaluation of germination tests, a global index including total germination percentage and the rate and uniformity of germination, expressed by the model parameters, was calculated using the formula: GI = GP/a + b(2.31/c ) where GI is the germination index, GP is the germination percentage at the end of the trial, and a + b(2.31/c ) is the time to reach 0.9 as a proportion of germination, which is derived from F(p, t). To evaluate the adequacy of the formula, GI was compared with the germination value proposed by Diavanshir and Pourbeik (1976).

The percentage of abnormal, diseased, and damaged seedlings was calculated in relation to total germinated seed instead of total number of seed used in every replicate. Because of the binomial distribution, data were arcsine transformed and subjected to analysis of variance (ANOVA). If interactions were present they were used to explain results. Otherwise, significant main effects were used with means separated according to least significant difference (LSD) in SAS (Statistical Analysis System, 2009).

RESULTS AND DISCUSSION Total germination and percentage of ungerminated solid and soft seed were affected by the Cultivar × Light × Temperature, Light × Temperature, and Cultivar × Temperature interactions (Table 1). Percentage of normal and

51

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NS,

∗ , ∗∗ , ∗∗∗ Not

∗∗∗

NS ∗∗∗

∗∗∗

NS

∗∗∗

∗∗∗

NS

∗∗∗

∗∗∗

∗∗∗

∗∗∗

∗∗∗

∗∗∗

NS

∗∗∗

∗∗

NS

∗∗∗

NS

∗∗

Abnormal seedlings (%)

NS NS NS NS

∗∗∗

∗

∗∗

Diseased germinated seed (%)

NS

∗∗∗

∗∗∗

NS

∗∗∗

∗∗∗

∗∗∗

Damaged germinated seed (%)

significant and significant at P ≤ 0.05, P ≤ 0.01, or P ≤ 0.001, respectively, ANOVA.

Cultivar (C) Light (L) Temperature (T) C×L C×T L×T C×L×T

Treatment

Normal seedlings (%)

Total germination (%)

ungerminated seed of onion.

∗∗∗

∗∗∗

∗∗∗

NS

∗∗∗

∗∗∗

∗∗∗

Ungerminated solid seed (%)

∗∗∗

∗∗

∗∗

∗

∗∗∗

∗∗∗

∗∗∗

Ungerminated soft seed (%)

Table 1: Responses to cultivar, light regime, temperature, and their interactions as they affect germination, seedling formation, and

Onion Seed Germination

abnormal seedlings produced and damaged seed germination percentage were affected by the Cultivar × Temperature and Light × Temperature interactions.

The percentage of ungerminated soft seed was affected by all interactions.

The percentage of germinated diseased seed was not affected by any interaction. The total germination percentage of normal or abnormal seedlings produced, percentage of diseased germinated seed, percentage of damaged germinated seed, and percentage of ungerminated solid and soft seed were significantly affected by cultivar, light, and temperature main effects. The exception was that light treatment did not affect the percentage of abnormal seedlings produced (Table 1).

The number of diseased germinated seed was statistically different due to some treatments but the biological significance of results is not clear (Table 2).

The cv. Red Creole had the lowest germination; the other cultivars had higher and similar (average 8.93) germination. The continuous dark produced, on average, one additional germinated seed than did continuous light.

There were small differences in normal germination of cultivars due to temperature and light (Figure 1). At 5◦ C all cultivars under continuous light had similar germination below 20%. At 5◦ C and continuous dark, cvs. Bianca Maggio Piattà and Royal Creole had higher germination, about 40%; ‘Texas Grano 502’ had higher germination, about 60%; and ‘Bianca Giugno Musonà’ had even higher germination, about 85%. Between 7.5 and 30◦ C all cultivars had similar germination of 80% or better regardless of the light regime.

At 35 and 40◦ C there were no differences in germination for individual cultivars except for ‘Bianca Maggio Piattà’, which had about twofold higher germination under continuous dark than continuous light at 35◦ C. Increasing temperature influences water uptake (Gulliver and Heydecker, 1973) and oxygen permeability of the seed coat (Come and Tissaoui, 1973).

At higher temperatures embryos require more oxygen, which becomes less Table 2: Mean separation for diseased germinated onion cultivars grown in light or dark.

Source

Cultivar Bianca Maggio Piattà Bianca Giugno Musonà Texas Grano 502 Red Creole Light Continuous dark Continuous light

Number diseased germinated

13.74a 11.73a 11.09a 8.93b 11.88a 10.86b

Means in a column followed by the same letter are not significantly different according to Scheffe adjustment, 5% probability level.

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100 90 Total germination percent

80 70 Bianca Giugno Musonà Bianca Maggio Piattà Red Creole Texas Grano 502

60 50 40 30 20 10

40

35

30

25

20

15

10

7.5

0 5

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Temperature Figure 1: Total germination percentage of onion cultivars in response to the interaction of Temperature × Light × Cultivar. Continuous dark (filled squares) or continuous light (empty circles). Error bars indicate the standard error of the mean.

available as the oxidation intensity of phenolic compounds increases. At optimum temperature there can be an interaction between water uptake and oxygen availability (Pimpini et al., 1993). The function of phytochromes A and B, which seem to have differential photo-sensory roles, is important in regulating seed germination (Quail et al., 1990).

Germination of normal, abnormal, and damaged seed was more affected by temperature than light (Figure 2). At 5◦ C germination was below 10% and increased to better than 70% at temperatures between 7.5 and 30◦ C. At 35–40◦ C germination was reduced to below 25%. At 5◦ C germination of abnormal seed was about 70% and decreased to around 10% for all other temperatures. At 5◦ C germination of damaged seed was about 25%, which decreased to below 10% up to 30◦ C and increased to about 35% between 30 and 40◦ C. Temperature affected normal germination for all cultivars (Figure 3).

At 5◦ C germination was below 10%, from 7.5 to 30◦ C germination was above 70%, and at 35 and 40◦ C germination was below 10%.

Abnormal seed germination was affected by temperature (Figure 4). At 5◦ C germination of all cultivars was above 70% and was reduced to around 10% at all other temperatures. Temperature level affected the percentage of diseased seed germinating (Figure 5). From 5 to 30◦ C germination was about 10% and at 35 and 40◦ C it increased to 35 and 48.5%. Abnormal seed germination was affected by temperature (Figure 6). At 5◦ C germination of all cultivars was about 20% and was reduced to around 10% between 7.5 to 30◦ C; at 40◦ C it increased to about 35%. Ungerminated soft seed of cultivars was generally below 10% regardless of temperature and light regime (Figure 7). Differences

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Temperature

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100 90 80 70 60 50 40 30 20 10 0 5

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Abnormal germinated

100 90 80 70 60 50 40 30 20 10 0 5

Normal (χ)

Onion Seed Germination

Temperature Figure 2: Normal, abnormal, and damaged germination percentage of onion cultivars in

response to the interaction of Temperature × Light. Continuous dark (filled squares) or continuous light (empty circles). Error bars indicate the standard error of the mean.

100 90 80

Normal (χ)

70 60

Bianca Giugno Musonà Bianca Maggio Piattà Red Creole Texas Grano 502

50 40 30 20 10

40

35

30

25

20

15

10

7.5

5

0 Temperature Figure 3: Normal germination percentage of onion cultivars in response to the interaction of

Temperature × Cultivar. Error bars indicate the standard error of the mean.

at some temperature and light regimes, although mathematically significant, are likely not biologically important.

The percentage of solid ungerminated seed varied due to treatment (Figure 8). On average for all cultivars and at 5, 40, and 35◦ C solid seed

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100 Bianca Giugno Musonà Bianca Maggio Piattà Red Creole Texas Grano 502

90 Abnormal germinated

80 70 60 50 40 30 20

40

35

30

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10

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0

5

10

Temperature Figure 4: Abnormal germination percentage of onion cultivars in response to the interaction

of Temperature × Cultivar. Error bars indicate the standard error of the mean.

40

35

30

25

20

15

10

7.5

100 90 80 70 60 50 40 30 20 10 0 5

Diseased germinated

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Figure 5: Diseased germination percentage of onion cultivars in response to temperature. Error

bars indicate the standard error of the mean.

percentages were highest (68%, 50%, and 53%, respectively), whereas for other temperatures, average nongermination percentage of solid seeds was <5%. The interaction of temperature and light induced the highest percentage of solid seeds at 5, 35, and 40◦ C, which are unfavorable to initiate germination (Fenner, 2000).

Suppression of germination at supraoptimal high temperatures is called thermoinhibition (Gallardo et al., 1991).

The a and b parameters were related to temperature (t) as follows: a = a1 exp(−a2 t); b = b1 + b2 t + b3 t2 .

Onion Seed Germination 100

Damaged germinated

Bianca Giugno Musonà

90

Bianca Maggio Piattà

80

Texas Grano 502

Red Creole

70 60 50 40 30 20 10 40

35

30

25

20

15

10

7.5

5

0 Temperature Figure 6: Damaged germination percentage of onion cultivars in response to the interaction of Temperature × Cultivar. Error bars indicate the standard error of the mean.

100

Bianca Giugno Musonà

90

Bianca Maggio Piattà Red Creole

Ungerminated soft (χ)

80

Texas Grano 502

70 60 50 40 30 20 10 40

35

30

25

20

15

10

7.5

5

0 Temperature Figure 7: Ungerminated soft percentage of onion cultivars in response to the interaction of Temperature × Light × Cultivar. Continuous dark (filled squares) or continuous light (empty circles). Error bars indicate the standard error of the mean.

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100 90 80 Ungerminated solid percent

70

Bianca Giugno Musonà Bianca Maggio Piattà

60

Red Creole Texas Grano 502

50 40 30 20 10

40

35

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10

7.5

0 5

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Temperature Figure 8: Ungerminated solid percentage of onion cultivars in response to the interaction of Temperature × Light × Cultivar. Continuous dark (filled squares) or continuous light (empty circles). Error bars indicate the standard error of the mean.

so that 1) a of the light condition produced the same trend for all cultivars, whereas a of the dark condition was similar for all cultivars except ‘Red Creole’ (Figure 9); 2) b of the light condition produced the same value for all cultivars except for cv. Bianca Giugno Musonà, whereas b of the dark condition was similar in cvs. Bianca Giugno Musonà and Red Creole (Figure 9); and 3) the c parameter was similar for all cultivars under light or dark (Table 3); the response of seed germination from 7.5 to 30◦ C under continuous light or continuous dark was analyzed using a complex modified Weibull function F(x, t) that considered both time (x) and temperature (t) variables and the parameters a1 , a2 , b1 , b2 , b3 , and c and the simplified model of Weibull function F(x, t) that depends on characteristics of the parameters described above.

The relationship of the Weibull simplified model parameters a, number of days required from imbibition to start of germination, and b, number of days required to induce germination in 63% of the population, in response to temperature at the two light levels generally decreased for all cultivars (Figure 9).

The only increase was for ‘Bianca Giugno Musonà’ from 25 to 30◦ C. The adequacy of the model F(x, t) was evaluated by means of regression analysis between expected relative cumulative frequency of the model and the relative cumulative frequency and between the expected relative cumulative frequency of the simple form of the model (achieved through reduction of the number of parameters using the similarity concept) and the observed relative cumulative frequency (Figure 10). A highly significant regression

Onion Seed Germination Parameter a Continuous dark 6

Continuous light 6

3

5

5

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4

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1,2,3,4

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1,2,4

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1

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10 15 20 Temperature

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Parameter b 14 12 10

14 2,3,4 12 1 10

2 4 1,3

8

8

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6

4

4

2

2

0

0 7.5

10 15 20 Temperature

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7.5

Figure 9: Relationship of Weibull parameters a and b with temperature under continuous dark

or light for all cultivars. 1, Bianca Giugno Musonà; 2, Bianca Maggio Piattà; 3, Red Creole; and 4, Texas Grano 502 (color figure available online).

Table 3: Relationship of germination to time (x) and temperature (t) under continuous dark or light for the cultivars: R 2 values and coefficients of the simple model of F(x, t). a= a1 exp .(−a2 t) Cultivara

R2

Continuous dark B. G. Musonà 0.9364 B. M. Piattà 0.9388 Red Creole 0.9830 Texas G. 502 0.9558 Continuous light B. G. Musonà 0.9686 B. M. Piattà 0.9748 Red Creole 0.9569 Texas G. 502 0.9358

b = b1 + b2 t + b3 t 2

a1

a2

b1

b2

b3

−b2 /2b3

c

5.415 5.415 21.55 5.415

−0.106 −0.106 −0.172 −0.106

17.35 22.88 17.35 18.09

−1.22 −1.61 −1.22 −1.19

0.0234 0.031 0.0234 0.0216

26.1 26 26.1 27.5

2.28 2.88 3.17 2.004

15.21 15.21 15.21 15.21

−0.171 −0.171 −0.171 −0.171

20.44 21.06 21.06 21.06

−1.5 −1.17 −1.17 −1.17

0.0308 0.0188 0.0188 0.0188

24.4 31.1 31.1 31.1

2.28 2.88 3.17 2.004

R2 = coefficient of determination; a parameter = time from imbibition at which germination starts; b parameter = time required to accomplish approximately 63% of germination, c parameter = defines shape of the distribution.

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Figure 10: Distribution of data with regression between expected relative cumulative frequency of the model and observed relative cumulative frequency from and between expected relative cumulative frequency of the model F(x, t).

between expected and observed values of the simple (R2 = 0.9617) and complex (R2 = 0.9563) relative frequency occurred. Because of the zero intercept and the close relationship of y = x, the model appeared to be valid to simulate germination trends (Table 3).

In all cases R2 values were higher than 0.93. The model coefficients indicated differences between treatments. The most important findings were as follows: 1) The optimum temperature to achieve maximum germination speed (T opt = −b2 /2b3 ) was from 26 to 27.5◦ C for all cultivars in the dark and from 24.4 to 31.1◦ C in the light. In the light the higher optimum mean temperature was 3◦ C greater than in the dark. 2) Parameter c was typical within each seed lot and varied slightly in the light.

The proposed model describes germination between seed of cultivars in response to temperature and light (Figures 11 and 12). In the dark and from 7.5 to 25◦ C, germination increased with increasing temperature for all cultivars with the highest value at 25◦ C, followed by a decrease at 30◦ C, except for cvs. Texas Grano 502 and Red Creole, for which there was no difference at 25◦ C. In the light germination increased from 7.5 to 30◦ C in all cultivars except cv. Bianca Giugno Musonà, which increased through 25◦ C and then decreased at 30◦ C. In all cultivars, incubation in the dark positively influenced germination from 15 to 25◦ C (Figure 13). The computation of F(x, t) demonstrated the number of days at which a specified proportion of germination was reached

Onion Seed Germination

Days

Days

Figure 11: Relative germination frequency of the different lots of onion under continuous dark

(PAR of 0.0 mol/m2 ·d−1 ) in relation to temperature from 7.5 to 30◦ C. Relative frequency based on F(x, t) simple model parameters (color figure available online).

Days

Days

Figure 12: Relative germination frequency of the different lots of onion under constant light

(PAR of 3.2 mol/m2 ·d−1 ) in relation to temperatures from 7.5 to 30◦ C. Relative frequency based on F(x, t) simple model parameters.

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Bianca Maggio Piattà

Bianca Giugno Musonà

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Figure 13: Germination index (GI) of onion cultivars in response to temperature under con-

stant dark (filled squares) or constant light (empty circles). GI based on total germination percentage and F(x, t) model parameters.

at a certain temperature. For all cultivars the minimum number of days to maximum germination was less in the dark than in the light. Regardless of cultivar, in the dark the increase in GI from 7.5 to 15◦ C was less pronounced; it was more pronounced from 15 to 25◦ C, followed by a decrease from 25 to 30◦ C except for ‘Texas Grano 502’, which increased up to 30◦ C. In the light, all except cv. Bianca Giugno Musonà exhibited the same increase in GI up to 15◦ C then more quickly up to 30◦ C. Maximum GI occurred at 30◦ C in all except cv. Bianca Giugno Musonà, for which it occurred at 25◦ C, followed by a decrease to 30◦ C. In all cases in light the values were lower than in the dark (Figure 13). Extreme low and high temperature inhibited germination, with a broad range of temperatures allowing favorable germination of all cultivars.

It is likely that sufficient and rapid germination will occur in the appropriate temperatures regardless of the presence or absence of light.

REFERENCES Bonner, F.T. and T.R. Dell. 1976. The Weibull function: A new method of comparing seed vigor. J. Seed Technol. 1:96–103.

Brewester, J.L. 1994. Onion and other vegetable Alliums, 1st ed. CABI Publishing, Wallingford, UK. Come, D. and T. Tissaoui. 1973. Interrelated effects of imbibition, temperature and oxygen on seed germination, p. 157–167. In: W. Heydecker (ed.). Seed ecology.

Butterworth, London.

Onion Seed Germination Diavanshir, K. and H. Pourbeik. 1976. Germination value. A new formula. Silvae Genet.

25:79–83.

Fenner, M. (ed.). 2000. Seeds: The ecology of regeneration in plant communities, 2nd ed. CABI Publishing, Wallingford, UK. Food and Agriculture Organization. 2008. Production yearbook for 2008. Food and Agriculture Organization, Rome, Italy.

Gallardo, M., M.D. Delgado, I.M. Sanchez-Calle, and A.J. Matilla. 1991. Ethylene production and 1-aminocyclopropane-1-carboxylic acid conjugation in thermoinhibited Cicer arietinum L. seeds. Plant Physiol. 97:122–127.

Gianquinto, G. and F. Pimpini. 1989. The influence of temperature on growth, bolting and yield of chicory cv. Rosso di Chioggia (Chicorium intybus L.). J. Hort. Sci. 64:687–695.

Gulliver, R.L. and W. Heydecker. 1973. Establishment of seedlings in a changeable environment, p. 433–461. In: W. Heydecker (ed.). Seed ecology. Butterworth, London.

Hartemann, H.T. and D.E. Kester. 1983. Plant propagation. Principles and practices.

Prentice-Hall, Englewood Cliffs, N.J. Johnson, N.L. and S. Kotz. 1970. Continuous univariate distribution. Houghton Mifflin, Boston.

Pimpini, F., M.F. Filippini, and G. Gianquinto. 1993. The influence of temperature and light on seed germination of radicchio (Chicorium intybus L. var. silvestre Bishoff).

J. Seed Sci. Technol. 21:69–83.

Quail, P.H., M.T. Boylan, B.M. Parks, T.W. Short, Y. Xu, and D. Wagner. 1990.

Phytochromes: Photosensory perception and signal transduction. J. Sci. 268: 675–680.

Statistical Analysis System. 2009. Version 9.1. SAS Institute, Cary, N.C.

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