Agriculture Reference
In-Depth Information
synthetic cultivars for your new employer. Indi-
cate each stage of the scheme on a year-by-year
basis.
After several rounds of clonal selection, you
have identified 4 potential high production par-
ent lines for developing a new synthetic (lines are
coded as A, B, C and D ). F 1 hybrid seed was pro-
duced from all parent cross combinations possible
and these F 1 s were evaluated in yield trials along
with the parent lines. From the yield (Kg) results
(below) indicate the three parent synthetic most
likely to be highest yielding and state the expected
yield.
SUMMARY
In summary, different crop species are more, or less,
suited for developing different cultivar types. Individ-
ual plant breeders have developed specific breeding
schemes that best suit their situation according to the
type of cultivar being developed, the crop species and
the resources (financial and others) that are available.
Irrespective of which exact scheme is used, breed-
ing programmes also differ in the number of individual
phenotypes that are evaluated in each scheme and in
the characters that are used for selection at each of the
breeding stages. To address the issue of numbers in the
breeding program, it is necessary to consider the mode
of inheritance of the factors of interest, and to have an
understanding of the relationship between the genetics
of their inheritance.
=
=
Parent A
18; Parent B
22;
Parent C
=
21; Parent D
=
25
A
×
B
=
25
A
×
C
=
26
A
×
D
=
24
B
×
C
=
30
B
×
D
=
21
C
×
D
=
24
THINK QUESTIONS
(4) Outline three characteristics of a crop species that
would merit consideration for developing hybrid
cultivars from that species.
(5) Outline the advantages and disadvantages of a
bulk breeding scheme and a pedigree breeding
scheme to develop inbred line cultivars
Many breeding schemes for inbred lines are
a combination of bulk and pedigree schemes.
Design a suitable bulk/pedigree breeding scheme
(it is not necessary to make notes on when spe-
cific characters are selected) that could be used
to develop superior inbred line cultivars. Outline
any advantages or disadvantages of your breeding
scheme.
(6) A hybrid breeding programme has identified six
superior inbred lines (A, B, C, D, E and F) and
these were inter-crossed in all combinations and
the F 1 populations evaluated for productivity in a
field yield trial. The results from each single cross
in the trial were:
(1) Disease resistance to powdery mildew has been
identified in a primitive and uncultivated relative
of barley ( Hordeum vulgare ). Research has shown
that the resistance is controlled by a single dom-
inant allele (notation
=
RR ). There is a 100%
reliable resistance screen test available. Diagram-
matically, outline a breeding scheme that could be
used to introgress this character into an existing
cultivar ('Golden Promise') which is susceptible
to powdery mildew (notation
=
rr ). The aim is
that the resulting resistant lines are to have at least
96% of the Golden Promise genotype.
Consider now that the disease resistance is con-
trolled by a single recessive allele, how would this
effect the breeding method you have described
above.
(2) Crop cultivars can be divided into pure-line culti-
vars, cross-pollinated cultivars, hybrid cultivars or
clonal cultivars. Briefly, describe the major prob-
lems that can be encountered or the attributes of
the crop types that can be utilized, when breeding:
a pure-line cultivar; a cross-pollinated cultivar; a
hybrid cultivar and a clonal cultivar.
(3) You have been appointed as alfalfa ( Medicago
sativa L.) breeder to develop crops for the Alfred
Alfoncia Seed Company Ltd. Outline a suitable
breeding scheme you will use to develop superior
×
=
×
=
×
=
A
B
34
A
C
29
A
D
27
×
=
×
=
×
=
A
E
33
A
F
20
B
C
31
×
=
×
=
×
=
B
D
34
B
E
26
B
F
19
×
=
×
=
×
=
C
D
29
C
E
30
C
F
18
×
=
×
=
×
=
D
E
35
D
F
10
E
F
19
 
Search WWH ::




Custom Search