5
Doubled Haploid: Advantages and Disadvantages Genotype formed as a result of the direct chromosome doubling of haploid cell is referred to as doubled haploid (DH). Doubled haploidy is a widely practiced breeding technique in modern crop breeding. It is not to choose or leave this technique because of its advantages and disadvantages, moreover, it is to improve its efficiency and circumvent its disadvantages with new/innovative technique/idea. Some of the major advantages and disadvantages of doubled haploids (DHs) are listed in here- ADVANTAGES: Doubled Haploidy is the fastest route to homozygosity in plants. It significantly shortens the breeding cycle thereby substantially reducing time to produce and release cultivars. Normally 8-10 breeding cycles (or years) are required to develop a new cultivar using traditional procedures. The DH method reduces that time by about 2-4 breeding cycles (or years) (Frauen 1994) i . Normally it takes 6-8 breeding cycles (or years) for developing nearly homozygous lines through traditional backcross method but 100% homozygosity can be fetched via doubled haploidy technique in 2-3 years. It gives possibility of seed propagation as an alternative to vegetative multiplication in ornamentals, and in species such as trees in which long life cycles and inbreeding depression preclude traditional breeding methods, doubled haploidy provides new alternatives. 1

Advantages and Disadvantages of Doubled Haploidy

Embed Size (px)

Citation preview

Page 1: Advantages and Disadvantages of Doubled Haploidy

Doubled Haploid: Advantages and Disadvantages

Genotype formed as a result of the direct chromosome doubling of haploid cell is referred to as doubled

haploid (DH). Doubled haploidy is a widely practiced breeding technique in modern crop breeding. It is

not to choose or leave this technique because of its advantages and disadvantages, moreover, it is to

improve its efficiency and circumvent its disadvantages with new/innovative technique/idea.

Some of the major advantages and disadvantages of doubled haploids (DHs) are listed in here-

ADVANTAGES:

Doubled Haploidy is the fastest route to homozygosity in plants. It significantly shortens the

breeding cycle thereby substantially reducing time to produce and release cultivars. Normally 8-

10 breeding cycles (or years) are required to develop a new cultivar using traditional procedures.

The DH method reduces that time by about 2-4 breeding cycles (or years) (Frauen 1994)i.

Normally it takes 6-8 breeding cycles (or years) for developing nearly homozygous lines through

traditional backcross method but 100% homozygosity can be fetched via doubled haploidy

technique in 2-3 years.

It gives possibility of seed propagation as an alternative to vegetative multiplication in

ornamentals, and in species such as trees in which long life cycles and inbreeding depression

preclude traditional breeding methods, doubled haploidy provides new alternatives.

Doubled haploids (DHs) are useful in fixing traits rapidly in desirable combinations in a

line/variety.

DHs facilitate hybrid breeding.

The probability of selecting progeny exceeding the performance of parents is higher than with

other breeding methods.

Doubled haploids segregate much simpler in the progeny of crosses, since their population

consists entirely of true breeding individuals.

It opens a unique way for the fixation of hybrid performance in homozygous lines, which would

avoid all problems with the production of hybrid seeds (Maluszynski et al. 2001)ii.

DHs applied in marker studies speed up the development of mapping populations and marker/trait

associations.

DH lines are often surprisingly vigorous since there is strong selection against recessive lethal

and subvital alleles in the haploid phase (Kuckuck et al. 1985)iii.

1

Page 2: Advantages and Disadvantages of Doubled Haploidy

Recombinations between linked loci are less frequent in DH lines than in pedigree-derived (PD)

lines as meiotic crossovers during the heterozygous generations of PD lines do not occur in DH

lines.

DH lines can be evaluated with more speed, accuracy and confidence, especially in respect to

quantitatively inherited traits such as yield and quality. Moreover, certain stages of doubled

haploid cultures are useful as targets for inducing mutation and transformation.

Androgenic structures induced from microspores in suspension make a perfect model to study

plant cell cycle regulation, cell division and early embryogenesis (Wedzony et al. 2009)iv.

DHs are a very useful tool for QTL mapping, particularly when the effect of the QTLs is small

(Devaux and Pickering, 2005)v.

When efficient technologies are available in relevant species and genotypes, the advantages of

DHS for breeding purposes can be fully exploited.

DISADVANTAGES:

Selection cannot be imposed on the population. But in conventional breeding, desirable traits can

be improved in population by selection for several generations.

Genetic gain from selection in heterozygous generations of PD lines is impossible in DH lines.

Though doubled haploidy shortens the time of breeding cycle quite efficiently, it is estimated that

the shortening of breeding time involves considerable cost which is sometimes twice as high as in

the conventional breeding process (Fuauen 1994) vi.

The over-usage of doubled haploidy may reduce genetic variation in breeding germplasm.

Unless haploid or doubled haploid production is highly effective, the DH lines are genetically

stable, and there is competence of macro- and microspores for regeneration into haploid plants,

the DH lines cannot be compared with traditional inbred lines. And these conditions cannot be

fulfilled by all species (Niemirowicz-Szczytt, 1997)vii.

Though it is emphasized that a high level of homozygosity is a significant factor for breeding F1

hybrids, the majority of DH lines are inferior to conventional inbred lines. The absolute level of

homozygosity, not encountered in conventional inbreeding, might be the reason for this. It is also

possible that the lack of natural selection in tissue culture is responsible for the fact that inferior

lines are not rejected in the early stages of production (Niemirowicz-Szczytt, 1997)viii.

2

Page 3: Advantages and Disadvantages of Doubled Haploidy

References

3

Page 4: Advantages and Disadvantages of Doubled Haploidy

i Frauen M. (1994): Use of biotechnology in breeding new varieties of winter oilseed rape in Germany. Bul. GCIRC, 10: 16–29.

ii Maluszynski M., Szarejko i., Barriga P., Balcerzyka A. (2001): Heterosis in crop mutant crosses and production of high yielding lines using doubled haploid systems. Euphytica, 120: 387–398.

iii Kuckuck H., Kobabe G. Wenzel G. (1985): Grundzüge der Pflanzenzüchtung. Walter de Gruyter & Co., Berlin and N. York.

iv Wedzony M., B. P. Forster, I. Zur, E. Golemiec, M. Szechynska-Hebda, E. Dubas, and G. Gotebiowska (2009): Progress in doubled haploid technology in higher plants. In: T. Alisher, B. P. Forster, S. M. Jain (Eds.), Advances in haploid production in higher plants, 1-33.

v Devaux, P., Pickering, R., (2005): Haploids in the improvement of Poaceae. In: Palmer, C.E., Keller, W.A., Kasha, K.J. (Eds.), Biotechnology in Agriculture and Forestry, Haploids in Crop Improvement II. Springer-Verlag Berlin Heidelberg Publ.

vi Frauen M. (1994): Use of biotechnology in breeding new varieties of winter oilseed rape in Germany. Bul. GCIRC, 10: 16–29.

vii Niemirowicz-Szczytt. (1997): Excessive homozygosity in doubled haploids- advantages and disadvantages for plant breeding and fundamental research. Acta Physiologiae Plantarum, 19 (2): 155-167.

viii Niemirowicz-Szczytt. (1997): Excessive homozygosity in doubled haploids- advantages and disadvantages for plant breeding and fundamental research. Acta Physiologiae Plantarum, 19 (2): 155-167.