Biomedical Engineering Reference
In-Depth Information
several BC1 crosses were evaluated. A total of 196 BC
2
progenies have been
developed and evaluated for bunchy top resistance and fiber qualities. Six promis-
ing clones have both the
AbBTV
resistance and good fiber quality.
During the evaluation, 1,300 seedlings from four BC
2
populations were manu-
ally inoculated with viruliferous aphids (
Pentalonia nigronervosa
). Each plant was
inoculated with 10 aphids that fed for 24 h on abaca leaves infected with the bunchy
top disease. Majority of the inoculated seedlings did not show any symptoms of the
bunchy top virus after 2 months. One hundred sixty-six inoculated seedlings
(12 from BC
1
-19
Abuab; 132 from BC
1
-20
Abuab', and 22 from 'BC
1
-19
Musa tex 51) were selected based on bunchy top virus resistance, plant vigor, and
resemblance of morphological characters to true abaca. The seedlings were
re-inoculated with the aphids for further confirmation of resistance.
To screen for desirable morphological traits, the BC
2
abaca hybrids were
selected and planted in the field with 2.5
2.5 m planting distance under coconut
trees as partial shade. The abaca hybrids were used for the evaluation of morpho-
logical traits, fiber qualities, and field resistance to bunchy top virus disease. These
abaca populations were also used to screen the primers and to identify crosses with
resistance to abaca bunchy top virus at the same time with good fiber qualities.
Recent Advances in Abaca Breeding
Marker-Assisted Breeding
Plant improvement, either by natural selection or through the efforts of breeders,
has always relied upon creating, evaluating, and selecting the right combination of
alleles. The manipulation of a large number of genes is often required for improve-
ment of even the simplest of characteristics. With the use of molecular markers, it is
now possible to trace valuable alleles in a segregating population and mapping
them. These markers once mapped enable dissection of the complex traits into
component genetic units more precisely, thus providing breeders with new tools to
manage these complex units more efficiently in a breeding program.
Genetic marker systems have numerous applications in
Musa
improvement.
These include increasing heritability of difficult to select characters via indirect
genotypic selection; complex quantitative traits may be resolved into simple Men-
delian loci; gene pyramiding for pest and disease resistance genes can be
performed; detailed genetic linkage maps can be constructed [
35
], and a
map-based gene cloning may be performed. Other uses include accurate identifi-
cation of clones [
36
,
37
]; the determination of evolutionary pathways between
clones [
38
]; the identification of duplications in germplasm banks; and monitoring
of somaclonal variation in micropropagated material for commercial use [
39
]. Iden-
tification of PCR markers for detection of A and B genome sequences in
Musa
was
also reported [
40
,
41
]. Three 10-mer RAPD primers produced unique banding
profiles for the differentiation of
M. acuminata
(A genome) and
M. balbisiana
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