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Using tissue culture to select for drought tolerance in bread wheat

H.M. AbdElGhany1, A.A. Nawar2, M.E. Ibrahim2, Sh.A. El-Shamarka2, M.M. Selim1 and A.I. Fahmi2

1 Field Crops Res. Dept. National Research Center, Egypt. Fax. 2023370931. Email: Hatem_m7@hotmail.com
2
Agronomy & Genetics Dept. Faculty of Agriculture, Minufiya Univ., Egypt.

Abstract

Breeding wheat varieties tolerant to drought stress is an important aim of the breeding programs in Egypt. The aim of this study was to examine the growth and regeneration of calli, derived from embryos of range of bread wheat varieties, under different mannitol concentrations (osmotic potentials = 0, 0.6, 0.9, and 1.2 MPa) and to compare any differences in growth with their growth and yield in field experiment. There were highly significant interactions between variety and mannitol concentration for callus survival and regeneration ability. Sakha 8 and Giza 157 gave the highest mean values for all callus traits and Sakha 8 and Sids 1 had the highest callus survival % and regeneration ability at high concentration of mannitol. Sakha 8 and Sids 1 also had the highest mean values for grain yield/plant in the field experiment when water was withheld after flowering. The varieties which had high and/or stable mean values for most traits under the two irrigation systems were Sahka 8, Giza 157 and Sids 1, suggesting the possibility of selection for drought tolerance under laboratory condition.

Media summary

Selecting for drought tolerance using tissue culture may provide a means to rapidly select for drought tolerance.

Key words

Wheat, water deficit, immature embryo culture.

Introduction

Wheat (Triticum aestivum L.) is the main diet for the Egyptian population and it is the main winter cereal crop grown in the country. Improving drought tolerance of wheat has long been a major objective of most breeding programs around the world because water deficits during some part of the growing period are common to most regions of the world where wheat is produced, including Egypt. Wheat breeders are looking for genetic diversity in which drought tolerance and yield potential can be combined.

Conventional plant breeding has improved yield partly by increasing drought tolerance of crop plants. Genetic improvement in grain yield has been demonstrated under both favorable and stressed conditions over a period of several decades. Therefore, breeders are continuing to look for genetic variability and more effective selection criteria, especially under unfavorable conditions. Recent developments in plant tissue culture techniques in combination with genetic engineering offer a much wider scope for improvement in drought tolerance. Plant cell tissue techniques offer several advantages for wheat improvement, particularly in respect of drought tolerance. Immature embryos of wheat have been widely used as an explant source to study embryogenesis, plant regeneration and somaclonal variations (Maddock et al. 1983; Cooper et al. 1986). This study was conducted to examine the level of variation to osmotic stress in calli of a range of genotypes and how this variation related to yields under drought in the field.

Materials and Methods

Laboratory experiments

Thus experiment was conducted during 2002/2003 and examined the growth of calli of the eight genoptyes (Sakha 8, Sakha 69, Giza 157, Sids 1, West bred, Falke, Hahn/Turaco and Kauz/Gen.) under different levels of osmotic stress, induced by different concentrations of mannitol. The experimental design was a factorial (8 genotypes x 4 osmotic potentials) with ten replications, each of 20 immature embryos. Immature embryo callus induction and maintenance were done using MS medium (Murashige and Skoog, 1962) supplemented with additional components. Callus was maintained by sub-culturing every 21-28 days on the same MS medium. Calli that were white to yellowish in colour, highly globular, nodular and friable were chosen for plant regeneration. Calli were classified into three groups according to its appearance, approximate number of somatic embryos on the surface of the callus, colour and regeneration capacity. The extracted immature embryos of eight wheat varieties were investigated in vitro at different mannitol treatments (0, 0.6, 0.9, and 1.2 MPa osmotic pressure).

Field experiments

A field experiment was conducted in the 2003/2004 growing season as a randomized complete block design with three replications. The eight varieties were sown in two adjacent field experiments and evaluated under two irrigation regimes, i.e., normal irrigation system and withholding irrigation system at heading. Each plot consisted of three rows, three meters long and 30 cm between rows. Plants within each row were 20 cm apart; to minimize border effects, adjacent plots were spaced by 60 cm. The plants were grown under adequate nutrition and weeds and diseases were controlled. Data were subjected to the analysis of variance according to Gomez and Gomez (1984) and significant differences for means were tested against L.S.D. values (Snedecor & Cochran, 1980).

Results and discussion

There were significant effects of Mannitol treatment, Variety and Mannitol x Variety interaction for callus survival %, and regeneration ability % traits (Table 1). Callus morphology was also significantly affected by mannitol treatment. These results indicated that there were marked genetic effects on frequency of callus survival % and regeneration ability. Many authors came to the same conclusion. Sears and Deckard (1982), He et al. (1986), Barakat and Abdel-Latif (1995 a, b and c). There were sharp decreases with increasing mannitol concentration in all callus traits, although there were significant differences in the responses among the varieties. At high concentrations of mannitol the least-affected varieties were Sakha 8 and Giza 157. (Table 2).

Table 1. Analysis of variance for immature embryos callus characters of all wheat varieties and mannitol treatments.

(** significant differences at 0.01 level of probability)

S.O.V

Immature embryo callus characters

Callus survival %

Callus morphology score

Regeneration ability %

Rep

38.82 **

0.19

2.53

Mannitol (M)

20049.59 **

10.48 **

17015.82 **

Varieties (V)

350.54 **

0.23

481.33 **

M x V

163.47 **

0.20

87.28 **

Error

4.40

0.68

7.31

Table 2. Effect of mannitol concentration (M) on the immature embryos callus traits of the eight wheat varieties.

Mannitol.

Varietal line of embryo

conc

Sakha 8

Sakha 69

Giza 157

Sids 1

West bred

Falke

Hahn/Turaco

Kauz/Gen

Mean

 

Callus survival (%)

0

83.3

76.3

85.3

92.3

92.7

74.0

91.3

91.3

85.8

6

80.7

73.3

83.0

83.3

90.0

70.7

89.3

88.0

82.3

9

65.7

50.3

65.7

48.3

61.7

51.7

40.0

42.0

53.2

12

34.7

23.3

38.0

20.0

25.7

18.0

16.0

15.7

23.9

Mean

66.1

55.8

68.0

61.0

67.5

53.6

59.2

59.3

61.3

LSD

LSD 0.05 for mannitol treatments (M) = 1.21, Variety (V) = 1.71 and M x V = 3.43

 

Callus morphology number

0

2.3

2.3

2.3

2.3

2.7

2.7

2.3

3.0

2.5

6

1.7

2.3

2.3

1.7

1.7

1.7

1.7

1.7

1.8

9

1.7

1.0

1.7

1.0

1.0

1.0

1.0

1.0

1.2

12

1.7

0.0

1.7

1.0

1.0

1.0

1.0

1.0

1.1

Mean

1.8

1.7

1.9

1.5

1.6

1.5

1.5

1.7

1.7

LSD

LSD 0.05 for mannitol treatments (M) = 0.48, variety (V) = ns, M x V = ns

 

Regeneration ability (%)

0

68.0

58.7

72.0

58.3

50.7

42.0

49.0

48.3

55.8

6

48.3

39.0

52.3

37.7

24.7

22.3

27. 7

27.0

34.8

9

8.3

1.3

9.3

1.0

3.7

0. 7

0.0

0.0

3.1

12

1.7

0.0

1.7

0.0

0.3

0.0

0.0

0.0

0.5

Mean

31.6

24.78

33.8

24.3

19.8

16.3

19.2

18.8

23.6

LSD

LSD 0.05 for mannitol treatments (M) = 1.56, variety = 2.21, M x V = 4.41

Reducing the supply of water in the field reduced grain yield per plant by 37.6%, mainly because of a reduction in grains per spike (24.5% reduction), but also because of reduced 1000-grain weight (8.0% reduction) (Table 3). The ranking of varieties was markedly different in the two irrigation treatments (Table 4). The varieties Sakha 8, Giza 157 and Sids 1 had desirable and stable mean values in most traits. These varieties also exhibited desirable values under laboratory condition and therefore may be worthy genotypes to use a parents for breeding for drought tolerance. These results also reported by Keim and Kronstad 1981, Kheiralla et al. (1997), Islam et al. (1998), Dencic et al. (2000) and Abo-Warda (2002).

Table 3 Main effects of water regime in field experiment on yield and components.

Character
Treatment

Plant height

(cm)

Time to 50% heading
(days)

Maturity

(day)

Grains /spike

1000 grain weight
(g)

No spikes /plant

Grain yield / plant
(g)

N

101.38

89.50

148.13

71.01

47.27

13.75

44.85

W

97.13

86.88

145.29

53.63

43.47

11.63

27.97

F test

*

*

*

**

*

**

**

Table 4 response of yield and yield components to water stress amongst variety

Variety

Plant height

(cm)

Time to 50% heading
(day)

Grains /spike

1000 grain weight
(g)

Grain yield /spike
(g)

Spikes /plant

Grain yield /plant
(g)

 

N

W

N

W

N

W

N

W

N

W

N

W

N

W

Sakha 8

102.0

101.7

88.7

86.0

80.0

68.0

44.2

40.6

3.4

2.7

17.0

15.0

59.1

43.9

Sakha 69

104.3

101.7

88.7

84.7

69.7

51.2

44.3

42.2

2.8

2.1

14.3

11.7

39.9

24.9

Giza 157

91.0

96.3

103.0

101.0

73.7

65.7

39.4

34.3

2.8

2.0

16.0

14.7

45.4

31.1

Sids 1

117.3

111.0

85.7

83.7

83.8

63.0

51.5

47.1

4.3

2.9

15.3

13.0

65.9

38.1

West bred

89.0

86.0

88.7

85.7

60.9

50.4

46.1

38.7

2.7

2.0

10.7

8.7

28.1

17.7

Falke

87.7

79.7

87.0

85.7

72.0

41.8

44.5

45.4

3.0

2.4

11.7

11.0

35.3

26.0

Hahn/Turaco

104.3

100.7

88.0

84.7

67.2

51.0

51.9

47.2

3.5

2.4

13.0

10.0

45.9

24.1

Kauz/Gen

115.3

100.0

86.3

83.7

60.9

37.9

56.2

52.3

3.3

2.0

12.0

9.0

39.2

17.8

F test

**

ns

**

ns

ns

ns

ns

Conclusion

These results support the selection for drought tolerant wheat varieties using the culture of immature embryos in vitro. The identified wheat varieties that had high and/or moderate yield potential besides desirable specific adaptation traits are useful genetic material in breeding for drought stress and could be combined to achieve optimum performance and adaptation under drought stress.

References

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