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eISSN: 2573-2919

Ecology & Environmental Sciences

Research Article Volume 4 Issue 6

Homozygosity and segregation ratio in Fgeneration of tomato for fruit morphology

Mehboob Ahmad,1 Aneela Kanwal,2 Mazhar Iqbal,2 Bilal Ahmed Khan,2 Muhammad Shahid,3 Adil Rehman,3 Farkhanda Khan,1 Imran Ullah ,1 Ibrar Hussain1

1Agricultural research institute, Dera Ismail Khan, Pakistan
2Hazara agricultural research station, Pakistan
3Agricultural Research station, Pakistan

Correspondence: Mehboob Ahmad Awan, Senior Research Officer, Wheat breeding section, Agricultural Research Institute, Dera Ismail Khan, Pakistan, Tel 00929667400900092966740090

Received: October 25, 2019 | Published: November 8, 2019

Citation: Ahmad M, Kanwal A, Iqbal M, et al. Homozygosity and segregation ratio in F4 generation of tomato for fruit morphology. MOJ Eco Environ Sci. 2019;4(6):258-261. DOI: 10.15406/mojes.2019.04.00162

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Abstract

Diversity in tomato shape is one of the most prominent traits which distinguish one variety of tomato from other. Our research aims to find the segregation ratio for fruit morphology in F4 lines and to determine the level of homozygosity within the lines. Plants with desirable traits were selected from F3 generation in 2017 and were sown as F4 generation in next season i.e 2018. Data were recorded for each plant in each line for fruit and blossom end shape and were analyzed through chi square test. Chi square test showed that more than 50% lines deviated from the expected ratio for fruit shape and showed significant difference between expected and observed ratios. Most of the obovoid-square fruit shaped F3 parents did not segregate further and produced all the obovoid-square shaped fruit plants in F4 generation. Obovoid fruit shaped F3 parents segregated into different fruit shapes in different ratios and did not show any homozygosity in F4 generation. Obovoid-pear fruit shaped F3 parents segregated into the Obvoid and pear shapes. Obovoid-cylindrical fruit shaped F3 parents did not produce any cylindrical fruit in F4 generation and segregated into square and obovoid shaped fruit plants. However, for blossom end shape, nearly all the lines segregated in F4 generation into flat blossom end and pointed blossom end shapes in the expected ratio i.e 3:1, respectively. Some lines did not segregate further for blossom end shape showing that those lines have attained homozygosity in F4 generation for the trait.

Keywords: tomato, F4, segregation, ratio, fruit, shape, blossom-end

Introduction

Tomato fruit shape is an important feature which determines its marketing and processing value.1 Fruit shape and related traits are clear and visible phenotypic markers which help determine the genotypic compositions of the breeding generations. In tomato breeding programme, segregation can be clearly observed in fruit shape more than other traits like: leaves, flower etc. The study of segregation in fruit shape in Fn generations determines whether the inbreeding lines have attained homozygosity or they are still in process of segregation.

Tomato has diversity in fruit shapes viz, rectangular, round, ovate, obovoid, and cylindrical etc.2 Diversity in fruit shape in cultivated germplasm are attributed to a great extent to four genes.3 These four major genes include: FAS which increases locule number and size,4 LC which increases locule number and fruit size,5 OVATE which gives obovoid fruit shape6 and SUN which gives an elongated fruit shape7 or the oxheart shape when associated to LC and FAS. However, elongated fruit shape is controlled by only one major locus.8

The study of tomato breeding lines at different stages helps in understanding the gene actions and genes responsible for tomato fruit morphology. The level of homozygosity for next breeding generations can also be determined by studying the lines for fruit morphology in breeding generations. There is dire need in tomato breeding programme to find at which stage tomato lines attain homozygosity for fruit shape and other parameters and to make selection on the basis of fruit shape according to preference of the local community. In our research programme, we aim to study the fruit and related characteristics and fix the desired fruit shape in later breeding generations.

Material and methods

In the year 2014, cross was made between two varieties: Roma (pear shaped fruit and semi pointed blossom end) and KHT5 (Obovoid- square shaped fruit and flat blossom end).The seed was extracted from the crossed-fruits and F1 generation was developed in next year i.e 2015. The F2 generation was advanced from F1 in year 2016.The selection was made in F2 generation and seeds were extracted from the selected plants to proceed to F3 generation. In Year 2017, F3 tomato lines were sown as nursery and 45 days plantlets were transplanted in the field and data were recorded on fruit traits. The plants with desired traits were selected from the F3 lines on individual basis and data for fruit morphology were recorded from the selected plants and seeds were extracted to develop F4 breeding lines. In next growing season i.e 2018, these selected F4 lines were sown as nursery in separate pots and after 45 days those lines were transplanted in the field in separate rows. Row to row distance was maintained to be 100cm and plant to plant distance was kept to be 50 cm. On fruit maturity, morphological data on fruits were collected from each plant of each line. The fruits were harvested on ripening and seeds were extracted.

Data were collected from each plant of each line for the following traits:

  1. Fruit shape
  2. Blossom-end shape.

Each plant was carefully observed for the collection of data on the above parameters.

Statistical analysis

Data were analyzed using the chi square test according to formula given in the below lines. 9:3:3:1 ratio was set as expected ratio for obovoid-square, square, obovoid and pear shape, respectively. While 3:1 ratio was set for flat and pointed blossom end.

X2=∑ (Observed – expected)2/expected

Where X2 is chi square

The chi square values were compared with the values in chi square table and the hypothesis was accepted or rejected on the basis of those values.

Results and discussion

Fruit shape

Chi square test shows that 13 of the 24 F4 lines deviated from the expected ratio i.e 9:3:3:1 (P>0.01) for fruit shape, while 11 lines followed the expected pattern of ratio for segregation for fruit shape (Table 1).

Most of the F3 lines having fruit shape Obovoid-square i.e RK1,RK5,RK6,RK7,RK8,RK9,RK10 and RK12 produced all the obovoid- square shaped fruits in F4 generation and did not show segregation for other fruit shapes. The chi square test showed non-significant difference between expected and observed ratios of segregation (Table 1). The results show that the lines were completely homozygous for the trait.

Entry Code

F3 parents

Homozygosity

Expected ratio

Observed ratio

Chi square

Sig/NS at 0.01

Fruit shape

%

Sq-obv:Sq:Obv:Pear (9:3:3:1)

Sq-obv:Sq:Obv:Pear

X2

 

RK1

Obv.Sq

100%

5.6:1.8:1.8:0.6

0 : 10 : 0 : 0

43.45

Sig

RK2

Obv.Sq

70%

5.6:1.8:1.8:0.6

7 : 0:3:0

3.51

NS

RK3

Obv

90%

5.6:1.8:1.8:0.6

1:0:9:0

33.47

Sig

RK4

Obv

60%

5.6:1.8:1.8:0.6

3:1:0:6

50.18

Sig

RK5

Obv.Sq

100%

5.6:1.8:1.8:0.6

10:0:0:0

7.77

NS

RK6

Obv.Sq

100%

5.6:1.8:1.8:0.6

10:0:0:0

7.77

NS

RK7

Obv.Sq

100%

5.6:1.8:1.8:0.6

10:0:0:0

7.77

NS

RK8

Obv.Sq

100%

5.6:1.8:1.8:0.6

10:0:0:0

7.77

NS

RK9

Obv.Sq

100%

5.6:1.8:1.8:0.6

10:0:0:0

7.77

NS

RK10

Obv.Sq

100%

5.6:1.8:1.8:0.6

10:0:0:0

7.77

NS

RK11

Obv-pear

70%

5.6:1.8:1.8:0.6

0:0:3:7

73.82

Sig

RK12

Obv.Sq

100%

5.6:1.8:1.8:0.6

10:0:0:0

7.77

NS

RK13

Obv.Sq

60%

5.6:1.8:1.8:0.6

3:1:6:0

11.36

Sig

RK14

Obv

60%

5.6:1.8:1.8:0.6

0:6:4:0

17.78

Sig

RK15

Obv

70%

5.6:1.8:1.8:0.6

0:3:7:0

20.99

Sig

RK16

Obv

80%

5.6:1.8:1.8:0.6

8:0:2:0

3.5

NS

RK17

Sq.cyl

50%

5.6:1.8:1.8:0.6

1:1:3:5

35.82

Sig

RK18

Obv

70%

5.6:1.8:1.8:0.6

1:2:7:0

18.5

Sig

RK19

Obv

40%

5.6:1.8:1.8:0.6

1:1:4:3

15.76

Sig

RK20

Obv

50%

5.6:1.8:1.8:0.6

4:1:5:0

6.73

NS

RK21

Obv

50%

5.6:1.8:1.8:0.6

1:5:4:0

12.08

NS

RK22

Obv.Cyl

80%

5.6:1.8:1.8:0.6

0:2:8:0

26.34

Sig

RK23

Obv.Sq

50%

5.6:1.8:1.8:0.6

3:0:2:5

34.04

Sig

RK24

Obv .Sq

50%

5.6:1.8:1.8:0.6

0:5:5:0

16.71

Sig

Table 1 Homozygosity %, expected ratio and observed ratio of segregation and chi square values for F4 lines of tomato for fruit shape
Obv-sq, obovoid-square; Obv, obovoid; Obv-Cyl, obovoid-cylindrical; sq-cyl, square- cylindrical; NS, non significant; Sig, sigificant at alpha level 0.01

F4 progeny of some F3 parental lines (obovoid-square) showed significant difference between observed and expected ratio. Among those lines RK2 segregated into 7:3 (Obovoid-square: square) as shown in Table 1. The ratio shows that the parental lines are heterozygous for fruit shape at F3 stage and obovoid-square genes are dominant over square shaped genes. RK13 segregated into obovoid-Square, square and obovoid shapes in the ratio of 3:1:6 (Table 1). There is trend of recessiveness from obovoid shape to obovoid-square and from obovoid-square shape to square shape as clear from the above findings. The line RK23 segregated into obovoid-square, obovoid and pear shape in 3:2:5 ratios (Table 1), respectively. The line RK24 segregated into square and obovoid shapes in the ratio of 5:5 (Table 1). The parental line RK1 produced only square shape fruits in F4 generation and did not segregate for other fruit shapes. The unexpected fruit shapes in F4 may be due to allelic variation in sun and fs8·1 loci that can cause elongated and square fruit shapes, respectively.9,10

All the obovoid shaped F3 parents segregated into different combinations in F4 generation and did not show homozygosity in any line which depicts those obovoid shaped genes were dominant over obovoid-square, square and pear shaped genes in F3. Some of the F4 progeny of these F3 lines showed significant difference between expected and observed ratio. The line RK3 segregated into square-obovoid and obovoid shapes in the ratio of 1:9. The line RK4 segregated into square-obovoid, square and pear shape in the ratio of 3:1:6, respectively (Table 1). The lines RK14 and 15 segregated into square and obovoid shapes in the ratio of 6:4 and 3:7, respectively. The line RK16 segregated into obovoid -square and obovoid shapes in the ratio of 8:2 and the chi square test shows that difference between observed and expected ratio was non-significant (Table 1). The lines RK20 and 21 whose F3 parents were obovoid shaped segregated into square- obovoid, square and obovoid fruit shape in different ratios i.e 4:1:5 and 1:5:4, respectively (Table 1). Unexpected ratios in fruit shapes from different parents of the same shape may be attributed to the cause as discussed by Gustavo et al.,11 who found that interactions between genes and uncharacterized modifiers also affect fruit shape: some lines have the duplication of the SUN gene and develop an ellipsoid instead of a long-shaped fruit. Moreover, differences in fruit shape of varieties carrying the OVATEFAS, and LC mutations shows that suppressors and enhancers of these genes are present within the cultivated germplasm. For example, accessions that carry the OVATE mutation display a range of fruit shapes from long and obovoid to round whereas accessions carrying LC mutation produce long, oxheart, round, or flat fruit.12

The F3 parents having obovoid-pear fruit shape segregated into obovoid and pear fruit shape in the ratio of 3:7 and it showed significant difference between the observed and expected ratio. Butler,13 found that O gene is responsible for both ovate and pear shape. Wua et al.,14 also reported that ovate alleles can be found in obovoid and ellipsoid varieties; which confirms the above statement. The F3 parents RK17 (square-cylindrical) and RK22 (Obovoid-Cylindrical) showed significant difference between observed and expected values for fruit shape and segregated into square, Obovoid-square, obovoid and pear shapes in the ratio of 1:1:3:5 and 0:2:8:0, respectively (Table 1). The ovate locus contributes in the formation of pear and cylindrical shapes15 therefore; cylindrical shaped parents can produce pear shaped progeny.

Blossom end shape

All the 24 lines showed non-significant difference between observed and expected values except the lines RK-16 and RK22 (Table 2).

Entry code

F3 parents

Homozygosity

Expected ratio

Observed ratio

Chi square

Sig/Non Sig at 0.01

Blossom end shape

%

Flat: pointed(3:1)

Flat: Pointed

X2

 

RK1

F

100

7.5 : 2.5

10:00

3.33

NS

RK2

F

100

7.5 : 2.5

10:00

3.33

NS

RK3

F

100

7.5 : 2.5

10:00

3.33

NS

RK4

F

100

7.5 : 2.5

10:00

3.33

NS

RK5

S.P

60

7.5 : 2.5

6:04

1.2

NS

RK6

P

100

0:10

0:10

0

NS

RK7

F

100

7.5 : 2.5

10:00

3.33

NS

RK8

F

70

7.5 : 2.5

7:03

0.13

NS

RK9

F

50

7.5 : 2.5

5:05

3.33

NS

RK10

F

70

7.5 : 2.5

7:03

0.13

NS

RK11

F

70

7.5 : 2.5

7:03

0.13

NS

RK12

P

100

0:10

0:10

0

NS

RK13

S.P

60

7.5 : 2.5

6:04

1.2

NS

RK14

F

80

7.5 : 2.5

8:02

0.4

NS

RK15

F

100

7.5 : 2.5

10:00

3.33

NS

RK16

S.P

90

7.5 : 2.5

1:09

22.53

Sig

RK17

F

100

7.5 : 2.5

10:00

3.33

NS

RK18

F

100

7.5 : 2.5

10:00

3.33

NS

RK19

F

100

7.5 : 2.5

10:00

3.33

NS

RK20

P

80

7.5 : 2.5

8:02

0.4

NS

RK21

F

100

7.5 : 2.5

10:00

3.33

NS

RK22

S.P

70

7.5 : 2.5

3:07

10.8

Sig

RK23

P

100

0:10

0:10

0

NS

RK24

F

80

7.5 : 2.5

8:02

0.4

NS

Table 2 Homozygosity %, expected ratio and observed ratio of segregation and chi square values for F4 lines of tomato for pointed and flat blossom end shape of tomato
F, flat blossom end; P, pointed blossom end; S.P semi pointed blossom end; NS, non-significant; Sig, significant

The progeny of F3 parental lines having flat blossom end RK1-4,7,15,17-19 and 21 showed non- significant difference between observed and expected values for blossom end shape in F4 generation (Table 2). The lines did not segregate for the trait and produced only flat blossom end in F4 generation. The lines have attained homozygosity for alleles for the trait in F4 generation which is due to presence of flat blossom end alleles in homozygous condition.

The F3 parental lines having flat blossom-end: RK8, 10 and 11 segregated into flat:pointed end in the ratio of 7:3, which is very close to expected values. The F3 parental lines (flat blossom end) RK 14,20 and 24 segregated into flat and pointed end in the ratio of 8:2. The ratio shows that flat blossom end genes were dominant; however, the lines were still heterozygous for the trait. Barten and Scott,16 found that cross between pointed and flat blossom end tomatoes bear flat blossom end tomatoes in F1 generation which shows that flat blossom end genes are dominant over genes responsible for pointed blossom end.

The F3 parental line RK9 segregated into flat and pointed end blossom shapes in the ratio of 5:5, respectively. The intermediate expression and segregation may be due to the reason as reported by Rick,17 that some genes for blossom end shape may also contribute intermediate expression for blossom end shape in heterozygous state.

Semi pointed blossom end parental lines RK5 and RK13 segregated into flat and pointed blossom end shapes in the ratio of 6:4 and showed no significant difference between observed and expected values. The result shows that there is dominance of flat blossom end alleles over pointed blossom end alleles. Other semi pointed-end F3 parental lines RK16 and RK22 segregated into flat and pointed end shapes in the ratio of 1:9 and 3:7, respectively .The F4 lines showed significant difference between observed and expected values. The ratios may be due to incomplete dominance for semi pointed end.

The F3 parental lines with pointed end RK 6, 12 and 23 produced all the pointed blossom-end shaped fruits in F4 generation and non-significant difference were observed between expected and observed values. The lines did not segregate further in F4 generation because of presence of recessive genes for pointed end in homozygous condition. Barten et al.,18 found that inheritance of pointed blossom end is due to recessive genes. However in heterozygous condition incomplete dominance can also be observed.

Conclusion

F3 lines segregating in F4 generation may deviate from the expected mendalian ratio for fruit shape. F3 parents having obovoid-square shape may show homozygosity for most of the F4 lines while F3 parents having obovoid fruit shape may not show homozygosity in F4 generation. Cylindrical F3 parents can segregate into obovoid and pear shapes in F4 generation. Flat blossom end shape is dominant over pointed end blossom shape.

Acknowledgments

None.

Funding

None.

Conflicts of interest

The authors declared that there no conflicts of interest.

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