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Title of Thesis

Javed Ahmad
Institute/University/Department Details
University of Agriculture, Faisalabad/ Department of Plant Breeding and Genetics
Plant Breeding
Number of Pages
Keywords (Extracted from title, table of contents and abstract of thesis)
wheat maize crossing system, bread wheat, haploid production, homozygous genotypes, zea mays l., triticum aestivum l., hybridization

Haploids are of great value as genetic and breeding tools in crop improvement. The major benefit of haploids is the compression of time required to generate homozygous genotypes. So, this technique provides breeders a very fast way of producing pure breeding lines. The production of wheat haploids from the intergeneric hybridization of wheat (Triticum aestivum L.) with maize (Zea mays L.) has been exploited to rapidly achieve homozygosit in wheat breeding programs.

To be efficient as a breeding tool, doubled haploids need to be produced in high frequency across all genotypes. In addition, production needs to be cost efficient, and the products need to be competitive with those produced by conventional breeding methods. In order to increase the efficiency of haploid production using the wheat x maize system, present studies were conducted in the Department of Plant Breeding and Genetics, University of Agriculture, Faisalabad, Pakistan during 1999-2000 to 2002-2003 to increase the output with respect to seed set and embryo formation.

Hand emasculation of wheat spikes is a highly labour intensive and time consuming process. Studies of different emasculation methods (Chapter 4), indicated that the laborious hand emasculation method can be replaced by a non-emasculation or hot water emasculation method (43 °C for 4 minutes).

Tiller culture was also evaluated as an alternative technology aimed at reducing the space requirements for the pollinated wheat heads, thereby enabling increased turnover (a reduced cycle time) for greenhouse materials. It was found that wheat spikes can be successfully cultured in a liquid medium just prior to anthesis, and up to embryo rescue. The grain growth ad embryo development in the detached wheat spikes in liquid culture closely resembled that observed in intact plants (Chapter 4). The technique of detached tiller culture was proved successful in wheat x maize crossing. This technique has many advantages over intact plant method like, time and space saving, delaying of pollination by storing tillers under cooler conditions, easy hot water emasculation of detached tillers and easy application of growth hormones. A liquid medium containing 40 g L-1 sucrose, 100 mg L-1,2,4,-D and 8 mlL-1 sulphurous acid was identified as the best medium for culture of wheat x maize crossed tillers.

To improve seed set, several hormones were used to treat pollinated florets. Treatment with a high concentration of 2,4-D (100 mg L-1) was effective; however, when combinations of 2,4-D + GA3 were applied, the seed set approached 100%. Similarly, an addition of 50 mg L-1 ABA to standard doze of 2,4-D (100 mg L-1) almost doubled the rate of haploid embryo formation.

Experiment conducted in the field to study the effect of pollen parents (Chapter 5) indicated that pollen sources significantly affected embryo formation. Crosses among selected pollen sources, ‘FSH-399’,’Composite-20 ‘Akbar’ and ‘73Q3’, identified pollen parents which gave levels of embryo formation as high as 53.0% when crossed on to wheat. The results of crosses between the best pollen sources and various female wheat parents of different ploidy levels (hexaploid and tetraploid) (Chapter ) indicated that hexaploid wheat perform better than tetraploid in crosses with maize. However, successful production of embryos at a relatively high frequency could be achieved in tetraploid wheats with ‘FSH-399’. The highest frequency of embryo formation (59.0%) was produced from a cross between the hexaploid wheat F1 ‘Cross-5 and ‘FSH-399’.

In Chapter 5 (Experiment-3), different pollen sources were examined to evaluate the efficiency of embryo formation. The results showed that crosses between the wheat F1 ‘Cross-3’ and the maize cultivar ‘Sadaf’ yielded on average 59.6% embryos/pollinated florets, and that ‘Sadaf as superior to other pollen sources. There were marked differences in embryo formation (p<0.01) among the synthetic maize cultivars (Chapter 4). The synthetic maize cultivar ‘Neelum produced the highest embryo formation (52.0%).The frequency of regenerated plants per pollinated floret was higher in the wheat x synthetic maize cross than for the wheat x hybrid or inbred line maize crosses. Hence, it was recommended that synthetic (open pollinated) maize cultivars should be preferred for use in crosses with maize

A series of hormones and hormone combinations were evaluated for their impact on embryo formation (Chapter 7. It was found that plant hormones affected embryo development in vivo following crosses between wheat and maize. The combination of GA3 (75 ppm) + 2,4-D (100 ppm) considerably improved embryo foration. ABA treatment likewise had a highly significant positive effect on embryo formation with 50 ppm of ABA being superior among all plant hormones and hormone combinations. Fifty ppm of ABA increased embryo formation to nearly double that produced in the control.

The development of improved culture media for the small for the small undeveloped embryos was also considered an important factor for effective plant regeneration (Chapter 8). The gelling agent Gel-gro, as well as the presence of copper and KNO3 were found to have a marked influence on embryo regeneration. All genotypes which performed poorly on basal media (MS, LS, B5 and half strength of MS) performed better on modified media. Eighty-five haploid plants from 100 cultured embryos were recovered using modified B5 medium, whereas the control (half strength MS) only produced 58.4% embryo regeneration.

There was also a significant effect of the plant development stage on fertility at the time of colchicines treatment. Plants at the 5-7 tillers stage showed improved plant fertility and reduced plant mortality than those treated at the 2-3 tillers stage.

One of the most important factors in chromosome doubling is the seeds obtained per treated plant, since this in turn determines how quickly these lines can be used in breeding programs. The addition of colchicines to media resulted not only in higher plant fertility than did conventional methods, but furthermore led to a huge increase in the number of doubled haploid seeds.

Cryogenic storage of maize pollen was considered as an alternative to growing maize plants year round in the green house (Cahpter 5). The viability of stored maize pollen indicated that, with refinements, pollen stored in liquid nitrogen has excellent potential for use in this system as compared to other storage methods (e.g. freeze or refrigerator). The results indicated that the fertilizing ability of maize pollen could be maintained for the duration of the experiment (180 days), provided that the pollen was dried to a 11-13% moisture content prior to storage.

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3322.3 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
218.31 KB
2 1 General Introduction 1
84.09 KB
3 2 Literature Review 8
394.49 KB
  2.1 Haploids In Plant Breeding 8
  2.2 Production Of Haploid Plants 13
  2.3 The Maize System 22
  2.4 Factors Affecting Wide Hybridization 28
  2.5 Chromosome Doubling 45
4 3 General Materials And Methods 51
401.76 KB
  3.1 Screening Of Wheat Genotypes Against Rusts 52
  3.2 Growing Plants For Crossing 53
  3.3 Te Male And Female Parents 54
  3.4 Emasculation Of Wheat 57
  3.5 Pollination 58
  3.6 Growth Regulator 60
  3.7 Detached Tiller Culture 61
  3.8 Embryo Rescue 62
  3.9 Culture Conditions 65
  3.10 Chromosome Doubling 68
  3.11 Data Analysis 69
5 4 Emasculation Techniques And Detached Tiller Culture In Wheat X Maize Crosses 70
468.27 KB
  4.1 Introduction 70
  4.2 Materials And Methods 72
  4.3 Results 77
  4.4 Discussion 89
6 5 Effects Of Pollen Sources On Embryo Formation In Wheat X Maize Crosses 96
257.49 KB
  5.1 Introduction 96
  5.2 Materials And Methods 97
  5.3 Results 99
  5.4 Discussion 109
7 6 Effects Of Different Ploidy Levels Of Wheat ( Hexaploids And Tetraploids ) On Seed Set, Embryo Formation And Haploid Production In Wheat X Maize Crosses 116
101.1 KB
  6.1 Introduction 116
  6.2 Materials And Methods 117
  6.3 Results 117
  6.4 Discussion 123
8 7 The Effects Of Plant Growth Regulators On Seed Set And Embryo Formation In Wheat X Maize Crosses 125
144.62 KB
  7.1 Introduction 125
  7.2 Materials And Methods 126
  7.3 Results 127
  7.4 Discussion 134
9 8 The Effects Of Culture Media On Regeneration Of Haploid Plants From Induced Immature Eembryos Resulting From Wheat X Maize Crosses 137
262.76 KB
  8.1 Introduction 137
  8.2 Materials And Methods 138
  8.3 Results 140
  8.4 Discussion 149
10 9 The Efficiency Of Chromosome Doubling In Haploids Derived From Wheat X Maze Crosses 154
215.3 KB
  9.1 Introduction 154
  9.2 Materials And Methods 156
  9.3 Results 157
  9.4 Discussion 163
11 10 General Discussion And Conclusion 168
103.56 KB
  10.1 Seed Development 168
  10.2 Improving Embryo Formation 169
  10.3 Improvement Of Haploid Plant Recovery 172
  10.4 Chromosome Doubling 174
  10.5 New Techniques 176
12 11 Summary 179
44.25 KB
13 12 References 183
370.48 KB
14 13 Appendices 211
572.75 KB