Maize Genetics Cooperation Newsletter vol 88 2014

 

 

The MaizeGamagrass Hybrids (2n = 56, 20Zm + 36Td) Carrying Genomes of the Lines Used for Obtaining Heterosis F1 (

 

P. A. Panikhin1, E. A. Abdyrakhmanova1, 3, C. A. Blakey2, and V. A. Sokolov1, 3

1 Cytology and Apomixis Laboratory, Institute of Molecular and Cellular Biology, pr. Akad. Lavrentieva 8/2, Novosibirsk, 630090 Russia

2 Department of Biology, Ball State University, Muncie, IN 47306-0440, USA

3 Vavilov Institute of Plant Industry, ul. BolŐshaya Morskaya 44, St. Petersburg, 190000 Russia

Continuing our study of apomixis in the hybrids between the maize (Zea mays, 2n = 2x = 20) and gamagrass (Tripsacum dactyloides, 2n = 4x = 72), we set the challenge to obtain a new set of 56-chromosome hybrids (2n = 56 = 20Zm + 36Td). Note that the main goal of this work was to combine in their genomes two haploid sets of the maize lines used for obtaining heterosis hybrids. The background for setting such goal was the earlier studies demonstrating that at least nine chromosomes of the wild parent were necessary for maintaining an apomictic reproduction in maize–gamagrass hybrids (Sokolov et al., 1998; Sokolov and Khatypova, 2000). This quantity of the gamagrass genetic material is able to considerably alter the expression of heterosis; in this case, its fixation via adopting the elements of apomixis from the wild relative should be regarded as groundless.

The 573MV and Kubanskaya 611SV lines (analogs of В73 and Mo17, respectively, utilized in breeding commercial heterosis hybrids) were used as cultivated parents. To obtain the F1 progeny, the chosen lines were pollinated with the pollen of tetraploid gamagrass earlier used to produce apomictic hybrids (Fig. 1).

The seed setting rate in the crosses where maize lines were pollinated with gamagrass was rather high, allowing for producing a considerable number of F1 hybrids (Figs. 2 and 3). However, this rate is somewhat lower as compared with that observed in the case of gamagrass self-pollination (Table 1). Note that a low percentage of set seeds observed in the years of 2009 and 2013 was associated with adverse weather conditions, which prevented an optimal pollination. Then the produced F1 seeds were planted in fields of the KubanŐ experimental station (Institute of Plant Industry); the grown plants (Figs. 4 and 5) were used in two variants of hybridization, namely, (1) pollination with the maize line giving heterosis F1 hybrids with the cultivated parent (Table 3) and (2) backcrossing with the cultivated parent (Table 2). The hybrids obtained in the first variant (2n = 56 = 20Zm + 36Td) will be used for assessing the expression of heterosis and the hybrids of the second variant analogous in their ploidy will serve as the control. When commencing this study, we expected to obtain segregation for the genes controlling apomixis, since the apomictic plants are heterozygous for this character. Thus, only part of the produced 46-chromosome hybrids (2n = 10Zm + 36Td) will further display this type of progeny production. Correspondingly, only the apomictic F1 plants will massively give functional caryopses after pollination with the maize. The remaining plants (non-apomictic) will develop sexual embryo sacs with the chromosome sets unbalanced as a result of meiosis and will mainly give inviable seeds.

This particular pattern was observed in the progenies of F1 hybrids pollinated with maize lines 573 and 611 (Tables 2 and 3).

Two classes of hybrids contrasting in the seed setting rate are evident in tables, namely, with a rate less than 5% and exceeding 20%.

The intermediate class with a seed setting rate of about 10% (7.7% in Table 2 and 11.5% in Table 3) is likely to result from concurrent development of sexual and diplosporic embryo sacs in a pollinated line. These data require further verification by hybridization with tester lines and cytological analysis.

The fact is that an Antennaria-type apomixis, observed in the gamagrass, is a genetically complex trait. We have earlier demonstrated that non-reduction (diplospory) and parthenogenesis in it are controlled in an independent manner (Sokolov, 2000) and the latter is likely to be subject to a polygenic control (Blakey et al., 2007). That is why the used gamagrass pollen may carry different combinations of the major and minor genes involved in the control of apomixis. As a result, this gives a fuzzy pattern of the well-filled grains in BC1 generation. Backcrossing of the apomictic F1 plants gives BIII hybrids (2n = 56 = 20Zm + 36Td), necessary for our further studies, at a rate of approximately 35% (Fig. 6). Therefore, their reliable production requires several hundreds of F1 plants. Currently, the available amount of seeds is sufficient for producing the necessary number of BIII hybrids of BC1 generation (Table 1).

References

1.             Sokolov, V.A., Kindigir, B, and Khatypova, I.V., Apomictically reproducing 39-chromosome maizeTripsacum hybrids, Genetika, 1998, vol. 34, no. 4, pp. 499506 [in Russian].

2.             Sokolov, V.A. and Khatypova, I.V., The development of apomictic maize: update, problems and perspective, Acta Biol. Yugoslavica, Series F. Genetika, 2000, vol. 32, no. 3. pp. 331353.

3.             Sokolov, V.A.. Independent inheritance and expression of apomeiosis and parthenogenesis in maizegamagrass hybrids, Dokl. Ross. Akad. Nauk, 2000, vol. 374, no. 2, pp. 280282 [in Russian].

4.             Blakey, C.A., Costich, D., and Sokolov V.A., Tripsacum research: a perspective from observation along a river to molecular genomics, Maydica, 2007, vol. 52, pp. 8199.


FIGURE SUMMARY

Figure 1. Ears of maize lines, their F1 reciprocal hybrids, and 46-chromosome F1 maizegamagrass hybrids (line 611 × T. dactyloides and line 573 × T. dactyloides).

IN FIGURE:

F1 Kubanskaya 611SV × T. dactyloides, 46 chromosomes (10Zm + 36Td)

self pollinated line Kubanskaya 611SV

F1 Kubanskaya 611SV × 573MV

F1 573MV × Kubanskaya 611SV

self pollinated line 573MV

F1 573MV × T. dactyloides, 46 chromosomes (10Zm + 36Td)

Figure 2. Seeds of 46-chromosome F1 maizegamagrass hybrids (line 611 × T. dactyloides and line 573 × T. dactyloides).

Figure 3. Seeds of line 611 and 46-chromosome F1 maizegamagrass hybrid (line 611 × T. dactyloides).

Figure 4. Inflorescences of T. dactyloides (left) and 46-chromosome F1 maizegamagrass hybrid (right).

IN FIGURE:

Inflorescence of T. dactyloides (2n = 4x = 72)

Ear of F1 hybrid line 573 × T. dactyloides, 46 chromosomes (10Zm + 36Td)

Figure 5. A plant of 46-chromosome F1 maize–gamagrass hybrid (line 573 × T. dactyloides).

IN FIGURE:

46-chromosome F1 maize–gamagrass hybrid line 573 × T. dactyloides, plant no. 4.8

Figure 6. A plant of 56-chromosome maize–gamagrass hybrid with a genomic composition of 10Zm (line 573) + 10Zm (line 611) + 36Td.

IN FIGURE:

BC1 of 46-chromosome F1 maize–gamagrass hybrid (line 573 × T. dactyloides) × line 611, plant no. 37.2

 

 


 

TABLES.

 

Table 1.

Seed setting rates of the maize lines 573 and 611 pollinated with T. dactyloides and self-pollinated gamagrass plants (2= 4= 72)

 

 

Pollination variants

 

Year

Number of pollinated ears

Number of set ears

Number of unset ears

Number of flowers

Number of grains

Seed setting rate, %

573 х T. dactyloides

2010

 

5

5

0

3040

890

29.3

611 х T. dactyloides

1

1

0

580

237

40.9

573 х T. dactyloides

2011

 

11

11

0

6688

2031

30.4

611 х T. dactyloides

17

17

0

9945

2015

20.3

573 х T. dactyloides

2012

 

70

70

0

42589

10810

25.4

611 х T. dactyloides

18

18

0

10442

5596

53.6

T. dactyloides self-pollination

2009

93

28

65

852

78

9.2

T. dactyloides self-pollination

2010

186

173

13

2076

1422

68.5

T. dactyloides self-pollination

2012

154

154

0

1719

1031

60.0

T. dactyloides self-pollination

2013

65

42

23

763

109

14.3

 

 

 

Table 2.

Seed setting rates of the 46-chromosome F1 maizegamagrass hybrids line 573 (Zea mays) × T. dactyloides backcrossed with line 573

 

BC1 variants

 

Year

 

Number of pollinated ears

Number of flowers

Number of set grains

Number of filled grains

Seed setting rate, %

F1 no. 1.9 х 573

2012

2

16

7

6

43.8

F1 no. 3.8 х 573

3

34

17

13

50

F1 no. 3.15 х 573

3

26

2

1

7.7

F1 no. 4.8 х 573

6

88

1

0

1.1

F1 no. 3.8 х 573

 

2013

15

193

39

29

20.2

F1 no. 3.9 х 573

2

25

0

0

0

F1 no. 3.15 х 573

2

29

0

0

0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 3.

Seed setting rates of the 46-chromosome F1 maizegamagrass hybrids line 573 (Zea mays) × T. dactyloides backcrossed with line 611

 

 

BC1 variants

 

Year

 

Number of pollinated ears

Number of flowers

Number of set grains

Number of filled grains

Seed setting rate, %

F1 no. 1.9 х 611

 

 

2012

8

81

31

24

38.3

F1 no. 3.8 х 611

12

159

78

58

49.1

F1 no. 3.9 х 611

1

25

1

0

4

F1 no. 3.15 х 611

5

76

1

0

1.3

F1 no. 4.8 х 611

12

192

0

0

0

F1 no. 1.9 х 611

 

 

2013

24

275

105

83

38.2

F1 no. 3.8 х 611

44

603

212

161

35.2

F1 no. 3.9 х 611

11

139

16

9

11.5

F1 no. 3.15 х 611

10

115

3

3

2.6

F1 no. 4.8 х 611

58

672

3

2

0.5

 


Figure 1. Ears of maize lines, their F1 reciprocal hybrids, and 46-chromosome F1 maizegamagrass hybrids (line 611 × T. dactyloides and line 573 × T. dactyloides).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2. Seeds of 46-chromosome F1 maizegamagrass hybrids (line 611 × T. dactyloides and line 573 × T. dactyloides).

 

 

 

Figure 3. Seeds of line 611 and 46-chromosome F1 maizegamagrass hybrid (line 611 × T. dactyloides).

 

 

 

Figure 4. Inflorescences of T. dactyloides (left) and 46-chromosome F1 maizegamagrass hybrid (right).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 5. A plant of 46-chromosome F1 maize–gamagrass hybrid (line 573 × T. dactyloides).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 6. A plant of 56-chromosome maize–gamagrass hybrid with a genomic composition of 10Zm (line 573) + 10Zm (line 611) + 36Td.

 

 

 

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