Hybrid Breeding II

Question 1

What are essential prerequisites for the prospects of hybrid breeding?

Answer 1

A (sufficiently) high degree of heterosis for economically important traits.
A suitable hybridization mechanism which allows
controlled mating of the two parental components on a large scale for an economic seed production.
prevents self-pollination.

Question 2

Compare the advantages and disadvantages of line vs. hybrid cultivars in
wheat and rapeseed.

Answer 2

Wheat has a low heterosis (mid-parent heterosis ~ 10%). The best line varieties are
very close in their performance to the best hybrids  Effort of creating hybrids is not
worth it respectively the higher price for the farmer buying the hybrid is not justified by
higher yield.
Rapeseed has a much higher heterosis compared to wheat (mid-parent heterosis
~45%). In this case the improvement is high enough that the effort of creating hybrids
is worth it and that the yield improvement is high enough for farmers to pay the higher
price for the hybrids

Question 3

What is the heterotic increase in inter-group hybrids and how can it be
explained?

Answer 3

The heterotic increase can be explained by the difference in the allele frequencies of
the two groups. So you need genetically divergent populations as hybrid parents to
get a heterotic increase. The effect is increasing with an increasing genetic
divergence between the mating partners.

Question 4

What types of source materials are used as base populations in hybrid
breeding?

Answer 4

As base populations can be used:
-Parental components of already existing hybrid varieties
-Primitive (wild) forms
-Material from seed banks
-Exotic material
Requirements for base population material
-The higher the performance level, the better
-Broad genetic variation
-All agronomical important traits: high yield, resistance and quality

Question 5

Compare the disadvantages of different types of tester in hybrid breeding.

Answer 5

Types of tester:
-Broad (population)
-Narrow (Inbred line, single cross)
-Strong(best line of opposite pool)
-Weak (poor line of opposite pool)
Broad tester: population (= opposite pool)
-Advantage: tester for GCA
-disadvantages:
 test candidates of no direct further use
 operationally difficult
 testing female plants is laborious
Tester = : representative sample of tester plants (> 12) for each
candidate
Tester = risk of assortative mating
Narrow tester: inbred line („SCA“ tester)
-Advantage: could be potential hybrid partner
 candidates are close to potential commercial hybrids, could save time
by stopping the testing procedure
-
Disadvantages: tests not only for GCA but for GCA + SCA
 SCA can mask GCA of lines and we could select
„inferior“ lines, if we change the hybrid partner
Weak tester:
Line with many disadvantageous genes, so all improvement in the progeny is due to
the lines I want to test (best choice in theory). Correct ranking of candidates is
possible

Strong tester: Masks differences among candidates. It’s hard to distinguish if the
improvement in the progeny due to the tester or due to the lines I want to test.
Ranking of test candidates might be not 100% correct. But a strong tester is the
choice in practice because the progeny might already be a potential hybrid variety.

Question 6

Describe the in vivo-method for production of DH-lines in maize. What are
the advantages of DH-lines in hybrid breeding of maize?

Answer 6

-You cross selected plants of a line with a so called inducer (father)
-This inducer leads to a certain number of haploid plants in the progeny
-These haploid plants carry only the genome from the mother, they are so
called maternal haploids
-By a treatment with colchicine, the poison of the autumn crocus, the maternal
haploids double their set of chromosomes  now you have doubled haploids
(DH)

Advantages:
-You get completely homozygous lines within one generation. Inbreeding takes
several generation to reach a level of homozygousity close to this  you save
a lot of time
-Complete genetic variance from the beginning
-Higher per se performance due to higher selection pressure during the haploid
phase
-Better results in early testing because there are no masked effects due to
hidden recessive alleles

Question 7

What are the advantages and alternatives in early-generation testing of lines
for combining ability?

Answer 7

Lines with a poor combining ability can be discarded at an early stage so you have
less material to test in later generations.
Alternatives (Early-testing is either So or S1):
1. Test S0 – plants for GCA  fast but laborious
2. Test S1 – plants for GCA  Less laborious; large seed quantities; preselection
for S1, but slower

Question 8

What are the advantages and alternatives for developing and testing of DH-
lines for combining ability?

Answer 8

Anther culture
-
Ovary culture

Question 9

Compare the disadvantages of different types of hybrids in maize.

Answer 9

2W hybrids have the best attributes in every trait except stability, here they reach the
lowest value (High yields can be achieved usually only in the first generation).
3W hybrids show a higher stability than 2W hybrids, but perform worse in all other
attributes.
Same for the 4W hybrids, but they already perform worse than 3W hybrids.
Worst performance in almost all attributes except of stability is shown by the topcross
hybrids. They show the highest stability.